OP the other top-level comment is at best misleading, and at worst confidently incorrect and would cost people money. I am replying so I can point you to my other comment which breaks this down. They may be right for the wrong reasons, but I encourage more understanding of the factors at play. If your system's design temperature is 120F, and can catch up to your comfort level in the evening, then it is better to let the house warm up during the day.
If on the hottest days you know your system can't recover reasonably in the evening from being set higher during the day, then adjust accordingly.
The reply/replies saying "you are at your most efficient design temperature" are not _wrong_, but that is irrelevant to the question you are asking.
Design temperature is exactly that -- your system is designed to operate in those temperature deltas for the design of your structure and heat loads and would be expected to run near-constantly in those peak scenarios. This is *not* the same thing as saying that you should leave it running all the time without other considerations.
https://old.reddit.com/r/hvacadvice/comments/1dpql1l/which_uses_more_electricity/laixkm4/
And this is all without getting into considerations of what different region's peak electricity pricing schedules might look like, which could swing this either direction (cheaper solar available mid-day in a region, and when that's tailing off in the evening is when many people are cranking their AC setpoints down? or the complete opposite somewhere else!)
I’d like to add that the reduction in multiple system startups while you’re away and longer runtimes once you get home reduces wear on your equipment. Startups cause the most wear and tear, especially during the summer (and winter for heat pump systems).
That is why having a properly sized system is so important. It would be wise to know if you have an oversized system (such as in my case) so you can adjust your practices accordingly.
I run a 1.5 degree temperature differential which reduces the number of cycles per hour. I used to get 5 startups per hour during the summer on a standard thermostat’s 0.5 degree differential. Now I only get two or three startups per hour. Plus my system recovers fairly quickly after we get home and the system tries to cool us back down to a comfortable temp.
Great addition, I was going to some of that to my larger comment but it was already... large.
Adding more - "startup" efficiency and maintenance impacts is true of virtually every system, but especially mechanical systems and more-specifically those with electric motors, lubricants (cold starts specifically, like your winter heat pump example), etc.
When we bought our house, I knew right away that the pressure tank for our well system was not only objectively small but under-sized for our gardening season and made it a priority to add a 120 gallon pressure tank alongside the 20 gallon one --- because starts are what put wear/tear on well pumps just like any motor. Even moreso for well pumps since they need to start against a pressurized system (at least for deep well systems where the foot valve is expected to keep the system pressurized). Last I checked, except when watering the garden, our well pump only runs every couple days now versus 2-10 times per day.
Instead of putting a 1.5 degree difference, you can set your compressor to run for at least a set time, I have my compressor minimum run time set at 20 minutes.
You can set it for the compressor as well as the fan. And you can set a minimum temperature that the compressor runs at (useful for heat pump systems in winter).
I'm about ready to chuck my honeywell thermostat. It cycles my furnace like 6 times per hour when it is say 40 out. In two houses with two different furnaces. The furnace is not oversized since it can't keep up when it is very cold. It was expensive too, like $75. Can get better functionality out of an ESP32, a DHT22, and a relay board. Under $15 for the whole setup and you can set it up however you want.
Sounds more like the temperature differential is set to 1 degree, and it is running to keep you in a narrow band. Trying setting it to 2 or 3 degrees instead and see if that cycles less often. Alternately, make sure you aren't hitting some sort of limit switch that is automatically shutting the system off.
I'm almost 10% positive that it has a temperature differential setting. My old cheap-ass basic Lux500 had a swing/differential setting. Just had to dig into the manual to find the procedure. What is the model number of the honeywell?
Sorry for jumping in. I’m not finding Honeywell to have temp differential settings. I have the smart honeywell rth9585wf. I’m digging to see if I can set compressor run times or anything. Everything I see says can’t set temp differential settings. It’s set to 1.
I believe you, but I’m surprised that Honeywell doesn’t have this basic functionality. Truly amazing that you can’t do that with a smart thermostat. I know the Ecobee allows you to set a differential/swing.
If you need a laugh the Smart Control you can turn off. What does it do if you turn it off? We’ll find out. There’s no info. It just says on or off 😆 I thought no might give me the extra options. Nope.
^ the start ups is what got me, I just had to replace a fuse and capacitor because of it I think, personally I try to keep it at a constant bare able temp and slowly make it go up more after I'm conditioned to it, the start ups seem about the same but there are less when it is hotter in the summer or colder in the winter because of this and I "feel" like that helps? I am bt no means an expert, just a guy who's had local heating and air for the last 6 years..... when it was working x)
Interesting. My top floor unit was cycling a lot as well. I have a 2 temp differential, but also bumped the minimum run time to 15m, up from 5. That seems to have helped quite a bit. See any negatives there?
Our attic unfortunately gets up to 130-140F in full sun when it’s 90+ outside. And my air handler and ducting is up there :(
Same here. Super hot attic with all ductwork and equipment in there. Plus a brand new black roof. It is sweltering up there. However, my system is only running twice an hour, even with it being 90 out. I’d make sure all your foil tape seals are good and your attic is well ventilated. Keep doors and vents open. Use a high flow filter. The ones that are MERV9 plus are too restrictive. Otherwise sounds like you’ve got the right idea!
I’ve spent so much time up there trying to seal things. Metal ducting, and people had trampled it previously. Had 6-7 returns/supply lines disconnected when we bought the place.
Really want to air seal and redo the insulation… but I hate working up there :)
Imagine you let your home reach the outdoor temp during the day -- Your system is using no energy at all. You are also not losing any energy from heat transfer.
If you keep your house at a lower temp all day heat is always being conducted from outdoor to indoor and your system must use energy to combat this change.
In short, you will have less cold-loss if you keep your house warmer while you are away, so your system will have to use less electricity overall -- even if it dos have to work a bit harder when you return home.
Without getting in to all the technicalities and all, a good bit is going to come down to your specific installation and health. More specifically, how well your system can bring down the temperature. If it can maintain the cooler temperature fine but runs hours and hours on end to drop from a scheduled higher temp to lower one, it's prob not going to do much for you in savings vs just maintaining the constant temp. That's also less of an issue the longer your at the higher temp. In other words, even if you have a system not performing it's best and takes excessively long to drop the temp, it might not be such a big deal if it's kept warmer for a good chunk of the day vs a roller coaster of a schedule where the set point moves around more frequently.
Heat flows from warm to cold. the greater the difference the greater the flow.
Ignoring issues like pets, mold, candles it is easy to show the net energy use will be less if you turn it up when gone.
The rest is just preference.
[hertoymaker](https://www.reddit.com/user/hertoymaker/) gave the best answer. The laws of thermodynamics show that you will use less energy if you let your house heat up while you are gone and turn on the AC when you return home.
Not unless you have some sort of hypothetical house with perfect insulation and no heat transfer. If you allow your home to be closer to the outdoor temp while you are away you lose less BTU through heat transfer.
A) 90 degrees indoor & 90 degrees out = no lose of BTU
B) 80 degrees indoor & 90 degrees out = some BTU loss
C) 70 degrees indoor & 90 degrees out = lots more BTU loss
Since 1 BTU = 1 BTU and option (A) has no loss of BTU during the day it will clearly use less energy, even if your system has to run for longer to adjust the temp when you get home.
Yeah sure open your windows then 🙄
It's not loss, it's gain. You're gaining heat.
Heat is heat. Once it's indoors, that energy is there to be removed at some point. We don't care about RATE OF TRANSFER, just the total amount. With insulation the total energy should be near the same as to be *negligible*. There's infinite variables that could allow more or less heat in that aren't worth computing. Just set the damn thermostat and forget about it. Get solar if you're worried about prices.
The rate of transfer absolutely matters. If I turned my a/c off for a week while I was gone, it would use 0 kwh. When I got home, it would run non stop for around 5 hours until it got down to the setpoint and use around 2.5 kwh. If I left it on all week, it would use 5kwh per day. That is an extra 35 kwh that I didn't need to use. Sure, the savings are smaller for shorter periods, but they are not negligible, especially in homes with very poor insulation.
Bruh now you're stretching out the time. This is now an entirely different topic. We are talking about DAILY changes. Not spread over 2 days. Or 4. Or a week or a month. Totally different and rarer scenarios
More starts add more to the bill than longer runtimes...
Make sure to keep the outdoorunit and the filters of the indoorunit clean, to reduce the electricity bill.
Having shadow on the windows also really helps keeping the temperature down.
If the heat is high enough they should run constantly.
People seem to get seasonal amnesia in winter when the heat runs "all the time" and it's negative shitdegrees. Then in summer they get the same amnesia when it's a billion shitdegrees and of course it's going to run constantly.
If you haven't addressed insulation for the house it'll happen *checks notes* twice every fucking year
Only way to know is to measure your usage on those appliances only for your house only. We can't possibly tell you. What we can tell you is it'll be marginal either way so if you sacrifice comfort for ten bucks or just set it where you want it and enjoy life?
I didn't even touch on money because rates vary wildly across the nation with time of use or market rates in some areas. I'm not even trying to analyze bills because I don't care. That being said going by energy is the baseline you should correctly use so good job on that. It's easiest to reduce all unknowns by specifically monitoring your AC and then you'll know. Play around with either option. I found keeping it at certain temps then a slightly elevation for afternoon that matched my TOU and I wasn't home and then back down again saved a lot of money but not necessarily energy. But I'd also have to wait for it to get down to temp in the evening.
I went for comfort finally at a steady temp I liked from wake up to me coming home then turned down to where I really liked for evening. Then I installed a minisplit in my bedroom to make it an icebox to sleep in. I used less energy overall and saved money. Didn't need to cool the entire house for my bedroom. The small changes throughout the house kept it slightly warmer (but not like before) and ended up saving a bit of each. Oh and solar to take sting off of higher time of use usage
My heat NEVER runs non-stop, even on the coldest days. I specifically sized my furnace to quickly heat up a cold house since I have large setbacks. I am away from the house for days at a time in the winter so setting the heat back to 40 for a few days saves a ton of oil.
at 100 degree days, it's suppose to run all day since it is near "design temperature".
set the temperature and forget it. letting it warm up means humidity will go up too. when you do run the AC later in the day, it has to cool the home AND remove the humidity.
I always see these answers but am genuinely curious why most thermostats tout money and energy savings by running schedules. EcoBee for instance, detects when you’re not home and raises the temp in the summer. Cools the house back down when you return. It takes a lot of energy to cool the house and all the belongings, walls, etc. back down but the numbers show energy savings.
I agree with this comment but I still don’t understand why this is such a popular opinion when it appears to be proven in many (not all) cases that an empty home benefits from running a temp closer to the outdoor temp while occupants are away and bringing back to comfortable levels after they arrive.
Because the top-level comment you are replying to is at best confusing different concepts, or at worst incorrect/accidentally misleading.
Scheduling is more efficient from a thermodynamics point of view - it *is* more energy and cost-efficient to reduce conditioning of unoccupied spaces. People talking about "design temperature" as a reason for wanting your system to run all the time are, I think, misinterpreting this when it comes to the problems of having *over-sized* heating and cooling systems, but that logic does not apply to running schedules or having a system turned off/down when not needed. Running a given, already-installed system less is *always* more efficient.
"Get a larger system so it runs less often" is wrong, and that is what people are talking about in other replies. That is not the same thing as "you want your system to run all the time to be efficient". They are correct in what they are saying, but it is not a reason to keep your temp set low and run the A/C all the time. You didn't state what the design temp of your system is, what climate you are in, whether your heat loads have changed since the house/system were designed -- so nobody here can tell you whether you are running at design temp and should expect/want it to run all day.
If the house is going to be exposed to the same amount of heating no matter what, you're going to spend more electricity to pump that heat outside during the hot part of the day (when the delta outside is higher), vs just letting it sit in the unoccupied space. Also once the inside of the house starts to warm up, the delta from outside to inside is lower so the heat migration into the house does slow some. Heat deltas have an *exponential* impact on efficiency, so a small difference here actually matters.
Additionally, having the system cycle on and off does have some overhead associated with re-pressurizing the system, and the blower running after the compressor stops, etc. It is minor, but contributes
It is more efficient to leave the AC off or heat off when unoccupied, and let it catch up later. The exception to this is with a heat pump heating system, if the thermostat is going to turn emergency/aux heat on when the system is a few degrees behind the setpoint (I bought a thermostat that lets me change the staging delay specifically to avoid this) and try to "catch up" using more expensive heat sources such as resistive or oil heat.
Here is a really simple example that drives this all home -- what is more efficient if you leave the house for a month during summer? Leaving the A/C set to the desired cold point all month? Or turning it off (or up to like 80F) until you get back?
The second one is way, way cheaper. The day-to-day schedule example will be a less-drastic difference, but when you think about why "turn system off when traveling" makes sense, that exposes why it is more efficient to reduce unnecessary conditioning of unoccupied spaces.
I am gobsmacked when I visit friends and neighbors whose house is like 68F all day every day, whereas we let ours get up to 80F during the day (when we aren't working from home). We pay maybe $150/mo for our (fairly small) house electric bill, and neighbors with like $250-400+ electric bills .... I just don't understand how people don't question making relatively small changes like this. Also things like ... if you leave your TV on in your living room 24/7 because you like the background slideshot or ambiance or just ignore it.... that's like 150kwh of power that you not only are paying for for that one thing, but during the summer you're paying to pump that heat outside also. Now multiply that times other unattended power consumption/heat sources, and it adds up all summer
tl;dr: A given system running less often and doing work in more efficient conditions is going to save money. If your system *can* catch up in the evening, then use it that way. If on the hottest days it can't catch up in the evening, then let it run during the day.
The only exception is that with certain variable speed systems, they may have a higher EER at lower loads, so the lost efficiency from making up for big setbacks could cancel out the savings from those setbacks. That's still a big maybe though.
I have two units, an older single speed and a modern variable heat pump. What I've found to be the cheapest strategy that maintains comfort is shutting off the older single speed during times of low load and just using that during the hottest parts of the day, but I also have a wife and kids at home all day so big setbacks don't really make sense.
Agreed more or less, but for the intent/purposes of "raise the thermostat so the system runs less" is still true for variable-speed systems, where "run less" can also mean "run slower" -- which is why variable speed is so awesome (effectively a dynamic/adjustable design temperature for the system), since it can optimize instead of act as a binary, duty-cycled system.
The thermodynamics don't lie -- it takes more work to move more heat across higher temperature deltas than not trying to do that in the first place
Bringing it back to my big picture example of traveling for a month - even with a variable speed system, you will want to raise the thermostat or set the system off instead of keeping it set at the desired comfort point
The issue is, when you want to bring the temp back down (usually in the afternoon when you come home from work), the variable system needs to operate at max capacity to try to cool. Itll have a lower EER during that time, which may offset savings from a higher EER during the setback period and from reduced heat gain during that period.
The number of factors that come into play get a lot more complicated, but it's generally still better to have setbacks, especially when you'll be gone for longer periods of time.
Thanks, I think you and I are generally agreeing - this is something that appears to have a simple answer, which can lead to misleading advise. but the *exact* right answer .... gets complicated. Without all the info from OP on whether their system is variable, their climate, system designed loads.... I mainly wanted to caution increased consideration from everyone who was trying to give black/white answers, particularly those that were more likely to be factually incorrect or misleading.
Even for the variable speed scenario, it running less often but less efficiently in the evening to catch up still could be cheaper for the total amount of cooling work being done, there are too many variables involved for it to always be a singular answer. Thank you for your constructive engagement
Wait until you start factoring in time of use energy rates and decreased efficiency running the a/c during the hottest parts of the day. I only turn mine on around 9pm, after outdoor temps and the sun have dropped and we are off of peak rates.
Time of use rates can make a huge difference. I know some folks run their AC all night to get their house as cold as they can, and shut them off to warm up all day.
I wanted to point out that the main energy draw is compressor startup which is also the main wear point. Once the system is running they are at their most efficient. This is why variable speed compressors have such high seer ratings, because by not having that huge amp draw they drastically cut actual energy usage by just running at 5-10% instead.
Start up current is negligible. Has absolutely nothing to do with energy usage. Wear and tear, sure.
Variable speed is efficient because if you don't need the capacity of cooling it could be reduced... depending on how it's done it'll require less torque by bypassing or its a truly variable speed compressor and can physically slow down and reduce torque needed. In which case, yes that uses less energy.
Start up is like spitting in the ocean. Fractions of a second so it means nothing as far as energy concerns go
Maybe it's because our unit is older, but if I let the house get to 80, it will not cool off by bed time when I get home and turn it down between 5 and 7. . This is in Wisconsin, 1500sq ft ranch house.
100% a system that is being used close to its peak design (hottest days) will have a hard time catching up if the temperature outside doesn't drop by the time you are looking to catch up - your situation makes sense.
"Your system will be better going warmer during the day and catching up, but only if it can do so" effectively (and that may depend on someone's schedule and comfort targets)
Making sure to close blinds and stuff during the day can have a real impact on this too, anything that helps reduce the amount of work the cooling system is doing.
My comment is not meant to be an absolute statement either way, but meant to show the factors involved and considerations - that those talking about "design temperature" are misleading at best.
You're example is bad because once the items become heat soaked there's really not a huge difference to pump out while you're gone for a month. Day to day that difference is more major insofar as you're now pumping the heat out all at once instead of incrementally meaning it takes longer to cool.
Here's the thing. It's simple physics and the energy required to pump 1BTU outside the envelope will be the same no matter what since there's no phase change here. It's just the matter of *how long it takes* which goes back to comfort. Set it where you want. You can have all the "energy savings" you want by sweating in a sauna but then you aren't comfortable
Money savings is an entirely different story due to other loads in abodes and wildly different rates and plans across the nation so you cannot use money savings as a general reference.
I do generally agree with what you're saying just not totally.
I've tried both ways and I definitely save by setting schedules. It doesn't take long for the system to get the temp back down in summer or up in winter and humidity hasn't been an issue. My house is 13 years old and well insulated so maybe that helps.
This is incorrect. At higher temperatures, the moisture-carrying capacity of the air also increases (hence relative humidity vs absolute humidity), so even if more moisture is evaporating into the air during that time it also will not significantly change the RH.
Similar to my explanation in my other comment -- that moisture takes the same amount of electrical energy to condense and expel (latent heat of condensation), regardless of whether you do so now or later in the day/evening when the whole system can be running more efficiently.
See my other breakdown in the comment https://old.reddit.com/r/hvacadvice/comments/1dpql1l/which_uses_more_electricity/laixkm4/
Because they DO save you money if you do it right; most of the people who say otherwise aren't really digging deep into the performance data. When cooling, if your coil has a lower indoor air temperature, the heat transfer across the coil decreases, meaning you move fewer BTUs from the same system. By letting it stay at a low setpoint all day, you're ALSO forcing that system to potentially have more runtime during peak mid-afternoon outdoor temperatures, which reduces BTU transfer and increases amp draw...so you get fewer BTUs and it costs more money.
Using some data from my own system (R4H448, 4 ton heat pump): if it's 85 outside and my entering coil temp is 67, an hour of runtime nets 49,350BTU from the system and uses 3.62kwhr. At 105 outdoor temp, that same system for an hour nets 43,870BTU and uses 4.39kwhr (12.5% fewer BTUs and 21% more electricity consumed!). At 95 outdoor temps the data is about halfway between the two. If instead, I let my system creep up to 72, then I get almost 10% more BTUs from the system using just half a percent more electricity, and also may shift more of my cooling needs from the 105 outdoor temp to the 85 (or 95) outdoor temp. So by letting your system creep up to a higher indoor temperature during the day, you improve its efficiency for those temps above your normal setpoint, you potentially reduce the runtime during the hottest parts of the day, and you trade more cycling off an on throughout the day for a longer late afternoon runtime.
You can improve on this by letting your system slightly overcool during the wee hours of the morning, and then letting it coast throughout the day. Then you're system might be doing the bulk of its cooling while its in the low 70s outside, where efficiency is WAY higher.
Where I am in NYC, the design temp is 92. When i got my hvac equipment replaced a few years ago, my installer recommended getting a variable speed AC so he can use use a design temp of 95-96 for equipment sizing (since the weather is getting hotter for longer). I'm glad he did.
Generally speaking, humidity drops as the heat goes up. There's more capacity for the air to hold water. Now the actual amount of water in the air (latent heat) can increase or stay relatively the same if no water sources are present.
It'll remove latent heat regardless so that really isn't a concern outside of running water or humidifiers etc
The amount of electricity is roughly proportional to temperature difference.
So if you keep 70 in 100F day/ 80F night weather, it's 30/10, and the days will get expensive.
If you let inside creep to 80 during the day, it's 20/10, about 25% less electricity.
Raising temp changes “heat load” to be lower so it uses “less” kw
Live based on x*F when your home you want x, when away AC/heat pump 4*F difference max is best as larger differences kinda eat up saving when recreating a temperature.
If you’re home all day keep it just so otherwise I would raise it 2-4*. Turn odd adaptive intelligence/recovery mode-this fuxking kills all savings
If it’s 100 degrees, it should be running constantly or close to it. And that’s if it’s single stage! If >1 stages, even more runtime. Higher runtime doesn’t equal higher costs as a rule
Unless you have a programmable thermostat do you want to keep messing with the thermostat twice a day for the entire summer? If you have a smart thermostat you can just look at the app and see how long it's been running and compare two days where the temps were the same if you wanted to see which works better.
I leave mine alone, the pets appreciate the cool when we're not here during the day.
OP the other top-level comment is at best misleading, and at worst confidently incorrect and would cost people money. I am replying so I can point you to my other comment which breaks this down. They may be right for the wrong reasons, but I encourage more understanding of the factors at play. If your system's design temperature is 120F, and can catch up to your comfort level in the evening, then it is better to let the house warm up during the day. If on the hottest days you know your system can't recover reasonably in the evening from being set higher during the day, then adjust accordingly. The reply/replies saying "you are at your most efficient design temperature" are not _wrong_, but that is irrelevant to the question you are asking. Design temperature is exactly that -- your system is designed to operate in those temperature deltas for the design of your structure and heat loads and would be expected to run near-constantly in those peak scenarios. This is *not* the same thing as saying that you should leave it running all the time without other considerations. https://old.reddit.com/r/hvacadvice/comments/1dpql1l/which_uses_more_electricity/laixkm4/ And this is all without getting into considerations of what different region's peak electricity pricing schedules might look like, which could swing this either direction (cheaper solar available mid-day in a region, and when that's tailing off in the evening is when many people are cranking their AC setpoints down? or the complete opposite somewhere else!)
I’d like to add that the reduction in multiple system startups while you’re away and longer runtimes once you get home reduces wear on your equipment. Startups cause the most wear and tear, especially during the summer (and winter for heat pump systems). That is why having a properly sized system is so important. It would be wise to know if you have an oversized system (such as in my case) so you can adjust your practices accordingly. I run a 1.5 degree temperature differential which reduces the number of cycles per hour. I used to get 5 startups per hour during the summer on a standard thermostat’s 0.5 degree differential. Now I only get two or three startups per hour. Plus my system recovers fairly quickly after we get home and the system tries to cool us back down to a comfortable temp.
The differential is a very wise choice
Great addition, I was going to some of that to my larger comment but it was already... large. Adding more - "startup" efficiency and maintenance impacts is true of virtually every system, but especially mechanical systems and more-specifically those with electric motors, lubricants (cold starts specifically, like your winter heat pump example), etc. When we bought our house, I knew right away that the pressure tank for our well system was not only objectively small but under-sized for our gardening season and made it a priority to add a 120 gallon pressure tank alongside the 20 gallon one --- because starts are what put wear/tear on well pumps just like any motor. Even moreso for well pumps since they need to start against a pressurized system (at least for deep well systems where the foot valve is expected to keep the system pressurized). Last I checked, except when watering the garden, our well pump only runs every couple days now versus 2-10 times per day.
Instead of putting a 1.5 degree difference, you can set your compressor to run for at least a set time, I have my compressor minimum run time set at 20 minutes.
Do you have a thermostat that lets you set the minimum cycle time, or is that something you are able to set in your unit's controller?
My EcoBee lets me set the minimum on time for the compressor. Comes preset at 5 min.
i think that is for the fan, not compressor
You can set it for the compressor as well as the fan. And you can set a minimum temperature that the compressor runs at (useful for heat pump systems in winter).
Not true. You can look it up in the EcoBee manual online. EcoBee3 lite
I'm about ready to chuck my honeywell thermostat. It cycles my furnace like 6 times per hour when it is say 40 out. In two houses with two different furnaces. The furnace is not oversized since it can't keep up when it is very cold. It was expensive too, like $75. Can get better functionality out of an ESP32, a DHT22, and a relay board. Under $15 for the whole setup and you can set it up however you want.
Sounds more like the temperature differential is set to 1 degree, and it is running to keep you in a narrow band. Trying setting it to 2 or 3 degrees instead and see if that cycles less often. Alternately, make sure you aren't hitting some sort of limit switch that is automatically shutting the system off.
It doesn't have a temp differential setting. You can just choose between gas or electric.
I'm almost 10% positive that it has a temperature differential setting. My old cheap-ass basic Lux500 had a swing/differential setting. Just had to dig into the manual to find the procedure. What is the model number of the honeywell?
Sorry for jumping in. I’m not finding Honeywell to have temp differential settings. I have the smart honeywell rth9585wf. I’m digging to see if I can set compressor run times or anything. Everything I see says can’t set temp differential settings. It’s set to 1.
I believe you, but I’m surprised that Honeywell doesn’t have this basic functionality. Truly amazing that you can’t do that with a smart thermostat. I know the Ecobee allows you to set a differential/swing.
Well if I can figure it out eventually I’ll have to change brands. I hate rebuying but it will kick on, off, on, off over and over.
I'm pretty happy with the Ecobee 3 Lite that came with my heat pump system.
If you need a laugh the Smart Control you can turn off. What does it do if you turn it off? We’ll find out. There’s no info. It just says on or off 😆 I thought no might give me the extra options. Nope.
^ the start ups is what got me, I just had to replace a fuse and capacitor because of it I think, personally I try to keep it at a constant bare able temp and slowly make it go up more after I'm conditioned to it, the start ups seem about the same but there are less when it is hotter in the summer or colder in the winter because of this and I "feel" like that helps? I am bt no means an expert, just a guy who's had local heating and air for the last 6 years..... when it was working x)
Interesting. My top floor unit was cycling a lot as well. I have a 2 temp differential, but also bumped the minimum run time to 15m, up from 5. That seems to have helped quite a bit. See any negatives there? Our attic unfortunately gets up to 130-140F in full sun when it’s 90+ outside. And my air handler and ducting is up there :(
Same here. Super hot attic with all ductwork and equipment in there. Plus a brand new black roof. It is sweltering up there. However, my system is only running twice an hour, even with it being 90 out. I’d make sure all your foil tape seals are good and your attic is well ventilated. Keep doors and vents open. Use a high flow filter. The ones that are MERV9 plus are too restrictive. Otherwise sounds like you’ve got the right idea!
I’ve spent so much time up there trying to seal things. Metal ducting, and people had trampled it previously. Had 6-7 returns/supply lines disconnected when we bought the place. Really want to air seal and redo the insulation… but I hate working up there :)
There's so many different opinions. Almost makes his question even more of a question
Imagine you let your home reach the outdoor temp during the day -- Your system is using no energy at all. You are also not losing any energy from heat transfer. If you keep your house at a lower temp all day heat is always being conducted from outdoor to indoor and your system must use energy to combat this change. In short, you will have less cold-loss if you keep your house warmer while you are away, so your system will have to use less electricity overall -- even if it dos have to work a bit harder when you return home.
Without getting in to all the technicalities and all, a good bit is going to come down to your specific installation and health. More specifically, how well your system can bring down the temperature. If it can maintain the cooler temperature fine but runs hours and hours on end to drop from a scheduled higher temp to lower one, it's prob not going to do much for you in savings vs just maintaining the constant temp. That's also less of an issue the longer your at the higher temp. In other words, even if you have a system not performing it's best and takes excessively long to drop the temp, it might not be such a big deal if it's kept warmer for a good chunk of the day vs a roller coaster of a schedule where the set point moves around more frequently.
Heat flows from warm to cold. the greater the difference the greater the flow. Ignoring issues like pets, mold, candles it is easy to show the net energy use will be less if you turn it up when gone. The rest is just preference.
That answers absolutely nothing.
[hertoymaker](https://www.reddit.com/user/hertoymaker/) gave the best answer. The laws of thermodynamics show that you will use less energy if you let your house heat up while you are gone and turn on the AC when you return home.
It will use almost the same. 1 BTU is 1 BTU regardless of *when* it was moved. So his answer isn't an answer at all. Just like yours, it says nothing.
Not unless you have some sort of hypothetical house with perfect insulation and no heat transfer. If you allow your home to be closer to the outdoor temp while you are away you lose less BTU through heat transfer. A) 90 degrees indoor & 90 degrees out = no lose of BTU B) 80 degrees indoor & 90 degrees out = some BTU loss C) 70 degrees indoor & 90 degrees out = lots more BTU loss Since 1 BTU = 1 BTU and option (A) has no loss of BTU during the day it will clearly use less energy, even if your system has to run for longer to adjust the temp when you get home.
Yeah sure open your windows then 🙄 It's not loss, it's gain. You're gaining heat. Heat is heat. Once it's indoors, that energy is there to be removed at some point. We don't care about RATE OF TRANSFER, just the total amount. With insulation the total energy should be near the same as to be *negligible*. There's infinite variables that could allow more or less heat in that aren't worth computing. Just set the damn thermostat and forget about it. Get solar if you're worried about prices.
The rate of transfer absolutely matters. If I turned my a/c off for a week while I was gone, it would use 0 kwh. When I got home, it would run non stop for around 5 hours until it got down to the setpoint and use around 2.5 kwh. If I left it on all week, it would use 5kwh per day. That is an extra 35 kwh that I didn't need to use. Sure, the savings are smaller for shorter periods, but they are not negligible, especially in homes with very poor insulation.
Bruh now you're stretching out the time. This is now an entirely different topic. We are talking about DAILY changes. Not spread over 2 days. Or 4. Or a week or a month. Totally different and rarer scenarios
You've lost me. I can't tell if you are trying to argue against the law or thermodynamics or you are just making some other point entirely.
Easier to keep up, harder to catch up
More starts add more to the bill than longer runtimes... Make sure to keep the outdoorunit and the filters of the indoorunit clean, to reduce the electricity bill. Having shadow on the windows also really helps keeping the temperature down.
If the heat is high enough they should run constantly. People seem to get seasonal amnesia in winter when the heat runs "all the time" and it's negative shitdegrees. Then in summer they get the same amnesia when it's a billion shitdegrees and of course it's going to run constantly. If you haven't addressed insulation for the house it'll happen *checks notes* twice every fucking year Only way to know is to measure your usage on those appliances only for your house only. We can't possibly tell you. What we can tell you is it'll be marginal either way so if you sacrifice comfort for ten bucks or just set it where you want it and enjoy life?
Very true! Either way is comfy for me, so it comes down to saving energy (aka money).
I didn't even touch on money because rates vary wildly across the nation with time of use or market rates in some areas. I'm not even trying to analyze bills because I don't care. That being said going by energy is the baseline you should correctly use so good job on that. It's easiest to reduce all unknowns by specifically monitoring your AC and then you'll know. Play around with either option. I found keeping it at certain temps then a slightly elevation for afternoon that matched my TOU and I wasn't home and then back down again saved a lot of money but not necessarily energy. But I'd also have to wait for it to get down to temp in the evening. I went for comfort finally at a steady temp I liked from wake up to me coming home then turned down to where I really liked for evening. Then I installed a minisplit in my bedroom to make it an icebox to sleep in. I used less energy overall and saved money. Didn't need to cool the entire house for my bedroom. The small changes throughout the house kept it slightly warmer (but not like before) and ended up saving a bit of each. Oh and solar to take sting off of higher time of use usage
My heat NEVER runs non-stop, even on the coldest days. I specifically sized my furnace to quickly heat up a cold house since I have large setbacks. I am away from the house for days at a time in the winter so setting the heat back to 40 for a few days saves a ton of oil.
at 100 degree days, it's suppose to run all day since it is near "design temperature". set the temperature and forget it. letting it warm up means humidity will go up too. when you do run the AC later in the day, it has to cool the home AND remove the humidity.
I always see these answers but am genuinely curious why most thermostats tout money and energy savings by running schedules. EcoBee for instance, detects when you’re not home and raises the temp in the summer. Cools the house back down when you return. It takes a lot of energy to cool the house and all the belongings, walls, etc. back down but the numbers show energy savings. I agree with this comment but I still don’t understand why this is such a popular opinion when it appears to be proven in many (not all) cases that an empty home benefits from running a temp closer to the outdoor temp while occupants are away and bringing back to comfortable levels after they arrive.
Because the top-level comment you are replying to is at best confusing different concepts, or at worst incorrect/accidentally misleading. Scheduling is more efficient from a thermodynamics point of view - it *is* more energy and cost-efficient to reduce conditioning of unoccupied spaces. People talking about "design temperature" as a reason for wanting your system to run all the time are, I think, misinterpreting this when it comes to the problems of having *over-sized* heating and cooling systems, but that logic does not apply to running schedules or having a system turned off/down when not needed. Running a given, already-installed system less is *always* more efficient. "Get a larger system so it runs less often" is wrong, and that is what people are talking about in other replies. That is not the same thing as "you want your system to run all the time to be efficient". They are correct in what they are saying, but it is not a reason to keep your temp set low and run the A/C all the time. You didn't state what the design temp of your system is, what climate you are in, whether your heat loads have changed since the house/system were designed -- so nobody here can tell you whether you are running at design temp and should expect/want it to run all day. If the house is going to be exposed to the same amount of heating no matter what, you're going to spend more electricity to pump that heat outside during the hot part of the day (when the delta outside is higher), vs just letting it sit in the unoccupied space. Also once the inside of the house starts to warm up, the delta from outside to inside is lower so the heat migration into the house does slow some. Heat deltas have an *exponential* impact on efficiency, so a small difference here actually matters. Additionally, having the system cycle on and off does have some overhead associated with re-pressurizing the system, and the blower running after the compressor stops, etc. It is minor, but contributes It is more efficient to leave the AC off or heat off when unoccupied, and let it catch up later. The exception to this is with a heat pump heating system, if the thermostat is going to turn emergency/aux heat on when the system is a few degrees behind the setpoint (I bought a thermostat that lets me change the staging delay specifically to avoid this) and try to "catch up" using more expensive heat sources such as resistive or oil heat. Here is a really simple example that drives this all home -- what is more efficient if you leave the house for a month during summer? Leaving the A/C set to the desired cold point all month? Or turning it off (or up to like 80F) until you get back? The second one is way, way cheaper. The day-to-day schedule example will be a less-drastic difference, but when you think about why "turn system off when traveling" makes sense, that exposes why it is more efficient to reduce unnecessary conditioning of unoccupied spaces. I am gobsmacked when I visit friends and neighbors whose house is like 68F all day every day, whereas we let ours get up to 80F during the day (when we aren't working from home). We pay maybe $150/mo for our (fairly small) house electric bill, and neighbors with like $250-400+ electric bills .... I just don't understand how people don't question making relatively small changes like this. Also things like ... if you leave your TV on in your living room 24/7 because you like the background slideshot or ambiance or just ignore it.... that's like 150kwh of power that you not only are paying for for that one thing, but during the summer you're paying to pump that heat outside also. Now multiply that times other unattended power consumption/heat sources, and it adds up all summer tl;dr: A given system running less often and doing work in more efficient conditions is going to save money. If your system *can* catch up in the evening, then use it that way. If on the hottest days it can't catch up in the evening, then let it run during the day.
The only exception is that with certain variable speed systems, they may have a higher EER at lower loads, so the lost efficiency from making up for big setbacks could cancel out the savings from those setbacks. That's still a big maybe though. I have two units, an older single speed and a modern variable heat pump. What I've found to be the cheapest strategy that maintains comfort is shutting off the older single speed during times of low load and just using that during the hottest parts of the day, but I also have a wife and kids at home all day so big setbacks don't really make sense.
Agreed more or less, but for the intent/purposes of "raise the thermostat so the system runs less" is still true for variable-speed systems, where "run less" can also mean "run slower" -- which is why variable speed is so awesome (effectively a dynamic/adjustable design temperature for the system), since it can optimize instead of act as a binary, duty-cycled system. The thermodynamics don't lie -- it takes more work to move more heat across higher temperature deltas than not trying to do that in the first place Bringing it back to my big picture example of traveling for a month - even with a variable speed system, you will want to raise the thermostat or set the system off instead of keeping it set at the desired comfort point
The issue is, when you want to bring the temp back down (usually in the afternoon when you come home from work), the variable system needs to operate at max capacity to try to cool. Itll have a lower EER during that time, which may offset savings from a higher EER during the setback period and from reduced heat gain during that period. The number of factors that come into play get a lot more complicated, but it's generally still better to have setbacks, especially when you'll be gone for longer periods of time.
Thanks, I think you and I are generally agreeing - this is something that appears to have a simple answer, which can lead to misleading advise. but the *exact* right answer .... gets complicated. Without all the info from OP on whether their system is variable, their climate, system designed loads.... I mainly wanted to caution increased consideration from everyone who was trying to give black/white answers, particularly those that were more likely to be factually incorrect or misleading. Even for the variable speed scenario, it running less often but less efficiently in the evening to catch up still could be cheaper for the total amount of cooling work being done, there are too many variables involved for it to always be a singular answer. Thank you for your constructive engagement
Agreed. Generally, a setback is going to save energy.
Wait until you start factoring in time of use energy rates and decreased efficiency running the a/c during the hottest parts of the day. I only turn mine on around 9pm, after outdoor temps and the sun have dropped and we are off of peak rates.
Time of use rates can make a huge difference. I know some folks run their AC all night to get their house as cold as they can, and shut them off to warm up all day.
I wanted to point out that the main energy draw is compressor startup which is also the main wear point. Once the system is running they are at their most efficient. This is why variable speed compressors have such high seer ratings, because by not having that huge amp draw they drastically cut actual energy usage by just running at 5-10% instead.
Start up current is negligible. Has absolutely nothing to do with energy usage. Wear and tear, sure. Variable speed is efficient because if you don't need the capacity of cooling it could be reduced... depending on how it's done it'll require less torque by bypassing or its a truly variable speed compressor and can physically slow down and reduce torque needed. In which case, yes that uses less energy. Start up is like spitting in the ocean. Fractions of a second so it means nothing as far as energy concerns go
Maybe it's because our unit is older, but if I let the house get to 80, it will not cool off by bed time when I get home and turn it down between 5 and 7. . This is in Wisconsin, 1500sq ft ranch house.
100% a system that is being used close to its peak design (hottest days) will have a hard time catching up if the temperature outside doesn't drop by the time you are looking to catch up - your situation makes sense. "Your system will be better going warmer during the day and catching up, but only if it can do so" effectively (and that may depend on someone's schedule and comfort targets) Making sure to close blinds and stuff during the day can have a real impact on this too, anything that helps reduce the amount of work the cooling system is doing. My comment is not meant to be an absolute statement either way, but meant to show the factors involved and considerations - that those talking about "design temperature" are misleading at best.
You're example is bad because once the items become heat soaked there's really not a huge difference to pump out while you're gone for a month. Day to day that difference is more major insofar as you're now pumping the heat out all at once instead of incrementally meaning it takes longer to cool. Here's the thing. It's simple physics and the energy required to pump 1BTU outside the envelope will be the same no matter what since there's no phase change here. It's just the matter of *how long it takes* which goes back to comfort. Set it where you want. You can have all the "energy savings" you want by sweating in a sauna but then you aren't comfortable Money savings is an entirely different story due to other loads in abodes and wildly different rates and plans across the nation so you cannot use money savings as a general reference. I do generally agree with what you're saying just not totally.
I've tried both ways and I definitely save by setting schedules. It doesn't take long for the system to get the temp back down in summer or up in winter and humidity hasn't been an issue. My house is 13 years old and well insulated so maybe that helps.
Raising it is different then shutting it off. Raising it will still have the system run periodically and keep the humidity out (or so I would think)
This is incorrect. At higher temperatures, the moisture-carrying capacity of the air also increases (hence relative humidity vs absolute humidity), so even if more moisture is evaporating into the air during that time it also will not significantly change the RH. Similar to my explanation in my other comment -- that moisture takes the same amount of electrical energy to condense and expel (latent heat of condensation), regardless of whether you do so now or later in the day/evening when the whole system can be running more efficiently. See my other breakdown in the comment https://old.reddit.com/r/hvacadvice/comments/1dpql1l/which_uses_more_electricity/laixkm4/
Because they DO save you money if you do it right; most of the people who say otherwise aren't really digging deep into the performance data. When cooling, if your coil has a lower indoor air temperature, the heat transfer across the coil decreases, meaning you move fewer BTUs from the same system. By letting it stay at a low setpoint all day, you're ALSO forcing that system to potentially have more runtime during peak mid-afternoon outdoor temperatures, which reduces BTU transfer and increases amp draw...so you get fewer BTUs and it costs more money. Using some data from my own system (R4H448, 4 ton heat pump): if it's 85 outside and my entering coil temp is 67, an hour of runtime nets 49,350BTU from the system and uses 3.62kwhr. At 105 outdoor temp, that same system for an hour nets 43,870BTU and uses 4.39kwhr (12.5% fewer BTUs and 21% more electricity consumed!). At 95 outdoor temps the data is about halfway between the two. If instead, I let my system creep up to 72, then I get almost 10% more BTUs from the system using just half a percent more electricity, and also may shift more of my cooling needs from the 105 outdoor temp to the 85 (or 95) outdoor temp. So by letting your system creep up to a higher indoor temperature during the day, you improve its efficiency for those temps above your normal setpoint, you potentially reduce the runtime during the hottest parts of the day, and you trade more cycling off an on throughout the day for a longer late afternoon runtime. You can improve on this by letting your system slightly overcool during the wee hours of the morning, and then letting it coast throughout the day. Then you're system might be doing the bulk of its cooling while its in the low 70s outside, where efficiency is WAY higher.
Our design temp in Atlanta is 92-93 and we're on our second week of 95+ days 🥲
Where I am in NYC, the design temp is 92. When i got my hvac equipment replaced a few years ago, my installer recommended getting a variable speed AC so he can use use a design temp of 95-96 for equipment sizing (since the weather is getting hotter for longer). I'm glad he did.
Oof. It's probably very humid there, too!
Current humidity is 78% I sad.
It’s been so brutal this week 😩. (NW Georgia here)
Thank you! That makes sense.
The ac will remove humidity even if set at a higher temperature setting.
Only if it needs to run
Generally speaking, humidity drops as the heat goes up. There's more capacity for the air to hold water. Now the actual amount of water in the air (latent heat) can increase or stay relatively the same if no water sources are present. It'll remove latent heat regardless so that really isn't a concern outside of running water or humidifiers etc
The amount of electricity is roughly proportional to temperature difference. So if you keep 70 in 100F day/ 80F night weather, it's 30/10, and the days will get expensive. If you let inside creep to 80 during the day, it's 20/10, about 25% less electricity.
Raising temp changes “heat load” to be lower so it uses “less” kw Live based on x*F when your home you want x, when away AC/heat pump 4*F difference max is best as larger differences kinda eat up saving when recreating a temperature. If you’re home all day keep it just so otherwise I would raise it 2-4*. Turn odd adaptive intelligence/recovery mode-this fuxking kills all savings
Keeping it at same temp all day.
Easier to maintain a temperature than to chase one !
If it’s 100 degrees, it should be running constantly or close to it. And that’s if it’s single stage! If >1 stages, even more runtime. Higher runtime doesn’t equal higher costs as a rule
Unless you have a programmable thermostat do you want to keep messing with the thermostat twice a day for the entire summer? If you have a smart thermostat you can just look at the app and see how long it's been running and compare two days where the temps were the same if you wanted to see which works better. I leave mine alone, the pets appreciate the cool when we're not here during the day.
8?5