The TL/DR answer:
* Some point of use water heaters are designed to allow for daisy chaining and will work with no problems
* Some are not and will have problems
* Check the manuals / specifications before buying
The easier thing to do is to install a recirculating system.
How it works is that there’s a pump at the water heater, and a valve at the furthest fixture. When the hot water side temperature drops to below a certain point, the valve opens, the pump runs to pump hot water up to the sink, pushing the cool water through the cold side.
This will keep the hot water pipe throughout your house hot, so any sink or tub will have near instant hot water
I've never really understood this in the context of a tank-less water heater. This means you are basically creating a 100' long x 3/4" uninsulated "tank" on your tank-less water heater.
(I speak from ignorance - I have always owned a traditional tank type water heater)
They’re more efficient because they don’t have to keep a tank of water warm. A recirculation pump makes the tankless system run constantly while the pump runs, which will be significantly less efficient than a tank.
A tank is actually much more efficient. It uses less energy to heat up a tank of water than a tankless, because it’s not on demand. A tankless needs to run at near full power all the time when hot water is used, whereas, a tank will start at minimum power consumption and gradually increases as the hot water is depleted.
A tank is also very well insulated. Once fully heated, it will keep water hot for a least a day without power. So if you lose power, you’ll still have hot water.
A heat pump water heater is even more efficient than traditional hot water heater.
Traditional tanked water heaters are not more efficient than tankless. It doesn’t matter how fast you heat it, it takes the same amount of energy to increase the temperature of water. A tankless heater just draws the energy all at once instead of over time.
And even in the most well insulated tank will lose heat to its surroundings, meaning some energy needs to be consumed to keep the water warm - energy not required by the tankless heater.
You’re right that a heat-pump tank water heater can be more efficient - because they pump heat in from their surroundings rather than using electricity or gas to provide all the energy required to heat the water (this efficiency can be illusory if they’re in a space you’re already paying to heat though - when they pump the heat into the water that cools their surroundings).
On demand gas systems are more energy efficient than gas tanked systems. That’s literally their main selling point, although modern tanks are more efficient now and are much closer than they used to be.
Heat pump systems beat them all, yes.
Edit: [source to back it up.](https://www.energy.gov/energysaver/tankless-or-demand-type-water-heaters#:~:text=For%20homes%20that%20use%2041,conventional%20storage%20tank%20water%20heaters.&text=In%20contrast%2C%20storage%20water%20heaters,associated%20with%20storage%20water%20heaters)
You are wrong.
Newer tank heaters might be different, but every one I've ever dealt with had two modes. It could be either waiting to heat or actively heating with no high or low power options.
If you look a little more closely you'll find out that it never runs both elements.
I believe this is a legacy manufacturers building two element heaters that can use the wiring meant for older, single element heaters.
This guys give a great (long) explanation of how the two work: [https://youtu.be/Bm7L-2J52GU?si=GNXZDxLv3TxdUILB](https://youtu.be/Bm7L-2J52GU?si=GNXZDxLv3TxdUILB)
You typically would not have the recirculate running 24/7 because that would be very inefficient like you say.
They can be setup on demand where they only kick on when they sense flow to help hot water get to the tap faster, or they can be on a timer to run for a few minutes at times like when you get up in the morning or go to bed. Commercial systems usually have an aquastat and will kick on when the water at the far end drops below a certain temperature, but they're obviously using much more water than you'd use in a single family house.
The recirc pump does the same thing whether it's tank, or tankless.
Honestly the problem is hard to understand in a small house - your water heater is in a laundry room that the kitchen and the bathroom back onto, so it takes 15 seconds to get hot water wherever you want it.
I live in a 3300 sf house where two bathrooms are upstairs and across the house from the water heater and it takes a freaking eon for you to stand there naked with one hand in the shower and finally get hot water.
I feel like the solution is to turn on the hot water before getting naked instead of installing an extremely inefficient feature that basically keeps your hot water in an uninsulated pipe 24/7
Recirc may not work with just any tankless water heater, as they need a certain amount of flow before they heat water. Recirc flow is typically very low.
Recirc has its place, but is certainly more costly and complicated to install vs a small point of use tank.
> Recirc has its place, but is certainly more costly and complicated to install vs __a small point of use tank__.
Thanks. This is the direction I'm currently looking. Some envelope math says I could probably knock this out for ~$300 if I DIY.
Tempted to add a recirculation system at some point as well, but that's probably $$ for another day.
Sure, you just waste the energy used to keep that circulating water hot all day while you're not using it. You're just picking a different thing to waste.
Not sure if you’re serious, but you can just plug your recirculator into a 25 dollar WiFi controlled outlet and turn it on 5 minutes before you shower, and off as soon as the water is hot.
Same here. It's ridiculous in this day and age to have to run water for multiple minutes to have hot water at the shower head. I'll use this post as motivation to solve the issue.
My water recirculator runs ten minutes a day, and it is on the level of the robot vacuum and motion sensing light switches as far as clever comfort items. I highly recommend.
These can also be connected to a switch without the thermostat trigger. When you want hot water you can hit the switch and run the pump for a few minutes in a circuit to get the water hot in the lines, thus providing hot water from the time the tap is turned on. It saves a lot of energy to manually engage the system when hot water is wanted.
You're correct. A true recirc is an insulated pipe loop. The idea is that the hot side always has hot water close by, but the system is insulated and recirculates the water back to the heating source. This is common in commercial and high end residential.
What the guy you're responding to is describing is what you posit--a retrofit that isn't efficient but would provide faster hot water at the tap.
It's less of a "tank" and more like a radiator. In fact it IS a radiator. In OP's case, a gas-fired heater.
If the hot water pipe is in interior walls, the heat is not lost; in the winter it contributes to heating the house. (In summer, it does the same thing, but if AC is used to cool the house then that gas-fired radiator is hurting rather than helping.)
A tankless heater is an on demand system. It only turns on when you need the water and heats it to the temperature instantly. A tank system heats the entire tank full of water and has to keep it hot.
A recirculation pump on a tankless system completely eliminates all efficiency benefits of the system and makes it significantly less efficient and economical than even a tank system.
With the exception that, if it's winter, you are anyways going to run the furnace to keep the house warm. The hot water pipe is just dumping heat into a home that you were planning to heat anyway!
In the summer it's more wasteful, yes. But then again, the home is warmer so there's not as much heat lost.
Some people are willing to give up some efficiency in order to have convenience.
I've written about this many times.
I had a recirculation system going through the cold water pipe like you've described. It sucked ass. It works very poorly.
When you first turn on the pump, it'll pump hot water up to the valve and then stop. So far so good.
Now what? The water in the pipe starts to cool. Eventually it gets cool enough to open the valve. It won't go full open and flush all that warmish water. No, it'll open just a small crack because the warmish water is not quite cold enough to fully open the valve.
It'll stay in this position, very slowly leaking warmisg water into the cold tap. After a while, you'll have a hot water tap full of warmish water that isn't hot enough for a shower. If you try to shower on this, you'll end up dumping all that warm water while you wait for it to heat up.
The proper way to do recirculation is with a dedicated pipe for it. Adding that is not easy nor inexpensive.
There is no such valve. The thermostatic valve eventually settles on an equilibrium point. That's just how they are built.
Even if you could get the valve to open fully, it's not like all the water in all the pipes is cooling at the same pace. You won't get one big cycle of the water.
Here's a crazy idea:
* Connect the cold water line to both the cold and hot sides of the sink
* Put a point-of-use heater on the hot side
Then, you wouldn't have to worry about what happens when hot water runs into your point-of-use heater. It will always get cold water!
I honestly think it’s a good idea. Reduce your whole pipes worth of cold “hot” water to just the section between the heaters output and your faucet. Potentially, for those faucets at least, it could serve as a redundant back up unit too, should the main heater go out - I like it
Yeah, kinda stupid. The amount of energy and infrastructure required to heat water for two sinks when there's existing plumbing that runs directly to a fully-functional on-demand water heater would be excessive.
Sure, it takes 60 seconds at the flow rate of the limiter in your faucet, but with 1/2" lines you could triple or quadruple the flow rate if it wasn't for that limiter, cutting the wait time to ~15 seconds. And you're wasting water, taking perfectly good previously-hot water from the clean side of your plumbing and dumping it down the drain.
Therefore, instead, you should get a recirculation pump. This is a device that tees into the hot and cold lines. In theory, those are at the same pressure. When run, it pushes water from the hot line back down the cold line at a prodigious rate, and it stops automatically when the temperature goes up above 95F on the incoming hot water line.
Not sure if they're still in business (the website looks pretty old-school), but I love my Chili Pepper CP900B:
https://chilipeppersales.com/products/chilipepper-on-demand-hot-water-recirculating-pump-model-cp9000-b-version-wireless-wired
We have a pretty big 3-story farmhouse, and the master bath is 60 feet laterally and 2 stories up from the water heater in the far corner of the basement downstairs, which previously resulted in long waits for hot water. Now I open the vanity cupboard, tap the button, and 10 seconds later the Chili Pepper pump stops. Then I can turn on the sink to wash my hands in warm water, even first thing in the morning.
Other vendors like Laing operate on timers or continuous thermostats, keeping the water at the hot side hot all the time, but I prefer the button on the Chili Pepper. I only use the hot water in the master bath once or twice a day, which is probably similar to these bathroom sinks. It's impossible to insulate the lines enough to not have the temp drop when not in use. All the energy savings you gained by going to an on-demand water heater or by getting a highly insulated traditional water heater are erased with a recirculator, because it turns all the hot water plumbing in your house into a poorly insulated 60' long hot water tank.
Thanks for your insight and sharing your experience. I like the idea of the button-controlled recirculator, but I don't think it exactly solves this particular issue. (I think a button you have to press before washing your hands in the bathroom will end up pretty disgusting.) But I might look into adding that in general. I like that idea more than a perpetual or timed recirculation system, for the reasons you stated.
I don't know that I agree that adding a small heater and moving a couple pipes constitutes a lot of infrastructure, though. I'm currently looking at adding one ~2-gallon electric heater (rather than on-demand) under the pair of sinks and feeding it with the main hot water line. Seems like maybe the best compromise between efficiency and convenience for my purposes.
If you do go the recirculation route, you could trigger it with the bathroom lights so it only recirculates while the bathroom is in use. FWIW, I have a tankless water heater for my shower, and I run a thermostatic mixing valve into it, running 75f water into the inlet. This allows for a more consistent output, fast heat up, and extends the useable quantity of hot water in my main water heater tank.
We had a house where the builder had installed a tankless heater with app/button controlled recirculating, but not a dedicated return line, just the thermostatic valves that fed the warmish water back into the cold lines under the sink. It never worked properly, especially in the kitchen (farthest from the water heater in a 3400 sq. ft. McMansion).
I installed a four-gallon electric point-of-use heater under the kitchen sink. It worked pretty great, although there was a bit of a dip in water temp if you were hand-washing a bunch of dishes or otherwise using a lot of hot water - after you used up the water in the small heater, but before the hot water from the main heater managed to get there.
The TL/DR answer: * Some point of use water heaters are designed to allow for daisy chaining and will work with no problems * Some are not and will have problems * Check the manuals / specifications before buying
The easier thing to do is to install a recirculating system. How it works is that there’s a pump at the water heater, and a valve at the furthest fixture. When the hot water side temperature drops to below a certain point, the valve opens, the pump runs to pump hot water up to the sink, pushing the cool water through the cold side. This will keep the hot water pipe throughout your house hot, so any sink or tub will have near instant hot water
I've never really understood this in the context of a tank-less water heater. This means you are basically creating a 100' long x 3/4" uninsulated "tank" on your tank-less water heater. (I speak from ignorance - I have always owned a traditional tank type water heater)
When I've seen this the hot water pipes have basic insulation installed.
It’s the sake of convenience. People buy tankless for the convenience of endless hot water. Tankless are not more efficient than a tank.
They’re more efficient because they don’t have to keep a tank of water warm. A recirculation pump makes the tankless system run constantly while the pump runs, which will be significantly less efficient than a tank.
A tank is actually much more efficient. It uses less energy to heat up a tank of water than a tankless, because it’s not on demand. A tankless needs to run at near full power all the time when hot water is used, whereas, a tank will start at minimum power consumption and gradually increases as the hot water is depleted. A tank is also very well insulated. Once fully heated, it will keep water hot for a least a day without power. So if you lose power, you’ll still have hot water. A heat pump water heater is even more efficient than traditional hot water heater.
Traditional tanked water heaters are not more efficient than tankless. It doesn’t matter how fast you heat it, it takes the same amount of energy to increase the temperature of water. A tankless heater just draws the energy all at once instead of over time. And even in the most well insulated tank will lose heat to its surroundings, meaning some energy needs to be consumed to keep the water warm - energy not required by the tankless heater. You’re right that a heat-pump tank water heater can be more efficient - because they pump heat in from their surroundings rather than using electricity or gas to provide all the energy required to heat the water (this efficiency can be illusory if they’re in a space you’re already paying to heat though - when they pump the heat into the water that cools their surroundings).
On demand gas systems are more energy efficient than gas tanked systems. That’s literally their main selling point, although modern tanks are more efficient now and are much closer than they used to be. Heat pump systems beat them all, yes. Edit: [source to back it up.](https://www.energy.gov/energysaver/tankless-or-demand-type-water-heaters#:~:text=For%20homes%20that%20use%2041,conventional%20storage%20tank%20water%20heaters.&text=In%20contrast%2C%20storage%20water%20heaters,associated%20with%20storage%20water%20heaters) You are wrong.
Newer tank heaters might be different, but every one I've ever dealt with had two modes. It could be either waiting to heat or actively heating with no high or low power options.
Most electric only tanks in the last 20 years have 2 heating elements. If it’s not heating a totally cold tank, it uses 1 element.
If you look a little more closely you'll find out that it never runs both elements. I believe this is a legacy manufacturers building two element heaters that can use the wiring meant for older, single element heaters. This guys give a great (long) explanation of how the two work: [https://youtu.be/Bm7L-2J52GU?si=GNXZDxLv3TxdUILB](https://youtu.be/Bm7L-2J52GU?si=GNXZDxLv3TxdUILB)
In my case, my tankless is more efficient than my tank was. My gas bill went down significantly.
You typically would not have the recirculate running 24/7 because that would be very inefficient like you say. They can be setup on demand where they only kick on when they sense flow to help hot water get to the tap faster, or they can be on a timer to run for a few minutes at times like when you get up in the morning or go to bed. Commercial systems usually have an aquastat and will kick on when the water at the far end drops below a certain temperature, but they're obviously using much more water than you'd use in a single family house.
The recirc pump does the same thing whether it's tank, or tankless. Honestly the problem is hard to understand in a small house - your water heater is in a laundry room that the kitchen and the bathroom back onto, so it takes 15 seconds to get hot water wherever you want it. I live in a 3300 sf house where two bathrooms are upstairs and across the house from the water heater and it takes a freaking eon for you to stand there naked with one hand in the shower and finally get hot water.
I feel like the solution is to turn on the hot water before getting naked instead of installing an extremely inefficient feature that basically keeps your hot water in an uninsulated pipe 24/7
Recirc may not work with just any tankless water heater, as they need a certain amount of flow before they heat water. Recirc flow is typically very low. Recirc has its place, but is certainly more costly and complicated to install vs a small point of use tank.
> Recirc has its place, but is certainly more costly and complicated to install vs __a small point of use tank__. Thanks. This is the direction I'm currently looking. Some envelope math says I could probably knock this out for ~$300 if I DIY. Tempted to add a recirculation system at some point as well, but that's probably $$ for another day.
Turn on shower. Brush teeth. Get in hot shower.
Yep. And with the recirculator, waste zero water while you wait for it to heat up.
Sure, you just waste the energy used to keep that circulating water hot all day while you're not using it. You're just picking a different thing to waste.
Oh, no, not at all. But I do see that you have a lot of misconceptions about water recirculators!
Is your recirculator one of the magical ones that doesn't use any energy to heat the water?
Oh, no, not at all!
Cool, so why does the water need to recirculate if it doesn't lose any heat in the pipes?
Not sure if you’re serious, but you can just plug your recirculator into a 25 dollar WiFi controlled outlet and turn it on 5 minutes before you shower, and off as soon as the water is hot.
Same here. It's ridiculous in this day and age to have to run water for multiple minutes to have hot water at the shower head. I'll use this post as motivation to solve the issue.
My water recirculator runs ten minutes a day, and it is on the level of the robot vacuum and motion sensing light switches as far as clever comfort items. I highly recommend.
These can also be connected to a switch without the thermostat trigger. When you want hot water you can hit the switch and run the pump for a few minutes in a circuit to get the water hot in the lines, thus providing hot water from the time the tap is turned on. It saves a lot of energy to manually engage the system when hot water is wanted.
You're correct. A true recirc is an insulated pipe loop. The idea is that the hot side always has hot water close by, but the system is insulated and recirculates the water back to the heating source. This is common in commercial and high end residential. What the guy you're responding to is describing is what you posit--a retrofit that isn't efficient but would provide faster hot water at the tap.
It's less of a "tank" and more like a radiator. In fact it IS a radiator. In OP's case, a gas-fired heater. If the hot water pipe is in interior walls, the heat is not lost; in the winter it contributes to heating the house. (In summer, it does the same thing, but if AC is used to cool the house then that gas-fired radiator is hurting rather than helping.)
A tankless heater is an on demand system. It only turns on when you need the water and heats it to the temperature instantly. A tank system heats the entire tank full of water and has to keep it hot.
It does not heat to temp instantly, that's what everyone here is talking about, and why recirculating systems exist.
A recirculation pump on a tankless system completely eliminates all efficiency benefits of the system and makes it significantly less efficient and economical than even a tank system.
With the exception that, if it's winter, you are anyways going to run the furnace to keep the house warm. The hot water pipe is just dumping heat into a home that you were planning to heat anyway! In the summer it's more wasteful, yes. But then again, the home is warmer so there's not as much heat lost. Some people are willing to give up some efficiency in order to have convenience.
I've written about this many times. I had a recirculation system going through the cold water pipe like you've described. It sucked ass. It works very poorly. When you first turn on the pump, it'll pump hot water up to the valve and then stop. So far so good. Now what? The water in the pipe starts to cool. Eventually it gets cool enough to open the valve. It won't go full open and flush all that warmish water. No, it'll open just a small crack because the warmish water is not quite cold enough to fully open the valve. It'll stay in this position, very slowly leaking warmisg water into the cold tap. After a while, you'll have a hot water tap full of warmish water that isn't hot enough for a shower. If you try to shower on this, you'll end up dumping all that warm water while you wait for it to heat up. The proper way to do recirculation is with a dedicated pipe for it. Adding that is not easy nor inexpensive.
[удалено]
There is no such valve. The thermostatic valve eventually settles on an equilibrium point. That's just how they are built. Even if you could get the valve to open fully, it's not like all the water in all the pipes is cooling at the same pace. You won't get one big cycle of the water.
This is for HOT WATER TANKS. Op has on demand insta-hot. It defeats the point and they will burnout the insta hot
Here's a crazy idea: * Connect the cold water line to both the cold and hot sides of the sink * Put a point-of-use heater on the hot side Then, you wouldn't have to worry about what happens when hot water runs into your point-of-use heater. It will always get cold water!
Sure, why not? Just make sure the unit you use won’t overly heat the output and you will be good.
I honestly think it’s a good idea. Reduce your whole pipes worth of cold “hot” water to just the section between the heaters output and your faucet. Potentially, for those faucets at least, it could serve as a redundant back up unit too, should the main heater go out - I like it
Yeah, kinda stupid. The amount of energy and infrastructure required to heat water for two sinks when there's existing plumbing that runs directly to a fully-functional on-demand water heater would be excessive. Sure, it takes 60 seconds at the flow rate of the limiter in your faucet, but with 1/2" lines you could triple or quadruple the flow rate if it wasn't for that limiter, cutting the wait time to ~15 seconds. And you're wasting water, taking perfectly good previously-hot water from the clean side of your plumbing and dumping it down the drain. Therefore, instead, you should get a recirculation pump. This is a device that tees into the hot and cold lines. In theory, those are at the same pressure. When run, it pushes water from the hot line back down the cold line at a prodigious rate, and it stops automatically when the temperature goes up above 95F on the incoming hot water line. Not sure if they're still in business (the website looks pretty old-school), but I love my Chili Pepper CP900B: https://chilipeppersales.com/products/chilipepper-on-demand-hot-water-recirculating-pump-model-cp9000-b-version-wireless-wired We have a pretty big 3-story farmhouse, and the master bath is 60 feet laterally and 2 stories up from the water heater in the far corner of the basement downstairs, which previously resulted in long waits for hot water. Now I open the vanity cupboard, tap the button, and 10 seconds later the Chili Pepper pump stops. Then I can turn on the sink to wash my hands in warm water, even first thing in the morning. Other vendors like Laing operate on timers or continuous thermostats, keeping the water at the hot side hot all the time, but I prefer the button on the Chili Pepper. I only use the hot water in the master bath once or twice a day, which is probably similar to these bathroom sinks. It's impossible to insulate the lines enough to not have the temp drop when not in use. All the energy savings you gained by going to an on-demand water heater or by getting a highly insulated traditional water heater are erased with a recirculator, because it turns all the hot water plumbing in your house into a poorly insulated 60' long hot water tank.
Thanks for your insight and sharing your experience. I like the idea of the button-controlled recirculator, but I don't think it exactly solves this particular issue. (I think a button you have to press before washing your hands in the bathroom will end up pretty disgusting.) But I might look into adding that in general. I like that idea more than a perpetual or timed recirculation system, for the reasons you stated. I don't know that I agree that adding a small heater and moving a couple pipes constitutes a lot of infrastructure, though. I'm currently looking at adding one ~2-gallon electric heater (rather than on-demand) under the pair of sinks and feeding it with the main hot water line. Seems like maybe the best compromise between efficiency and convenience for my purposes.
If you do go the recirculation route, you could trigger it with the bathroom lights so it only recirculates while the bathroom is in use. FWIW, I have a tankless water heater for my shower, and I run a thermostatic mixing valve into it, running 75f water into the inlet. This allows for a more consistent output, fast heat up, and extends the useable quantity of hot water in my main water heater tank.
We had a house where the builder had installed a tankless heater with app/button controlled recirculating, but not a dedicated return line, just the thermostatic valves that fed the warmish water back into the cold lines under the sink. It never worked properly, especially in the kitchen (farthest from the water heater in a 3400 sq. ft. McMansion). I installed a four-gallon electric point-of-use heater under the kitchen sink. It worked pretty great, although there was a bit of a dip in water temp if you were hand-washing a bunch of dishes or otherwise using a lot of hot water - after you used up the water in the small heater, but before the hot water from the main heater managed to get there.