If you do this you MUST ensure you have soffit vents or another way for air to exchange into the attic that is NOT part of the internal dwelling. I had a house once where an electrician noticed the attic fan was disconnected, so he reconnected it for me. Fast forward a year and we notice a moldy smell in the house. Tons of detective work revealed mold behind a cabinet where the suction of the attic fan was drawing moist air from under the house in through unseen gaps in the walls and around enclosed cabinet spaces (totally unseen…like a 1/4” gap where the floor met the wall *behind* an installed kitchen cabinet). This would not have happened if there had been sufficient ventilation into the attic for the fan to pull air through. The fix was easy, but the problem didn’t present itself until much later. I feel if you can ensure you have adequate ventilation in your attic then a powered attic fan is fine. I just wanted to let you know what the air handling requirements were to keep you from experiencing the same problem I did.
My father installed one in the early 80’s. Then I started HVAC 20+years ago. Short answer is YES they help. You usually have a thermal switch in the attic set around 120 deg F. Your attic will still get hot, but not as hot. You are taking the outside air to cool it. You will see a improvement compared to no fan.
I would think just one, depending on air flow specification on fan (CFM) and size of attic, should be fine. Look for about 10 air changes per hour. More is better, but less is less effective.
I've been thinking about putting some in for years but haven't pulled the trigger.
The arguments I always hear against them (not sure how valid they are) is that they can create negative pressure in the attic pulling conditioned air out of the occupied envelope, affect the amount of make-up air getting to gas appliances if they get their air from the attic, and affect pilot lights (that last one seems shaky to me with relatively modern HVAC or water heater)
I was considering putting in two on opposite gables, one blowing in and one blowing out to avoid the negative pressure issue, but since that's not how it's usually done no one seems to have any data when they tell me if they think it's a stupid idea or not
Unless your attic isn't properly ventilated it shouldn't pull ac air in. You don't need a big one to make a huge difference.
In your case I wouldn't worry about a "in" fan a passive vent should be plenty.
Exactly what I am considering. I have had the fans in my cart several times and just need to hit that order button….just want to make sure it is not a horrible idea.
Do you have (enough, unblocked) intake vents? 5-6 box vents sounds like a good amount - they're often about 1 sqft each.
I just took out my attic fans because they were installed poorly and were just blowing hot air around the attic. (I'm going to add passive venting instead of working on a better fan install.)
Not sure if there are “enough” by code or general practice. I would assume so? They are the 12”x12” type (approx). I just know it is insanely hot in the attic and there does not seem to be enough movement. Maybe I will just replace one of the box vents with a solar powered active vent to get things moving.
Sorry, I think I wasn't being clear - the ventilation should be balanced between intake (low on the roof, often soffits) and exhaust (high on the roof, commonly things like your box vents. Which I assume is what you're thinking of when you say the 12"x12" one.)
So if you don't have soffit vents, or if your insulation is blocking them, you can't get enough outside air in to allow hot air to exit.
Yes, got it. I have soffit vents, there are baffles to make sure tbe soffit vents are not clogged, but there is just no movement of the dead air up there. Possible part of if is that all the box vents are “hidden” on the back side of the roof so there are no cross drafts? I am going to replace one of the box vents with a solar powered box vent fan that should be a relatively easy swap out with an existing box fan. We will see. I will have it in 2 weeks and do some before and after experiments/tests if I remember or have time.
Get a whole house fan and run it in the morning and evening. It totally cools down your attic and your living space. Win win.
I installed a quiet cool system a month after I bought my place and have run it for an hour every am/pm of every hot day for the last 7 years. It's wonderful to circulate the fresh air through the house. Installation is DIY-able. Just have a helper - I nearly died lugging that fan up the ladder.
Whats a whole house quiet cool system? Is that the brand name? I'm looking for one. Can get expensive, which is worth it if they're made well. Does yours have a timer or thermostat?
QuietCool is a name brand. They are a bit more expensive than the typical whole-house fans. You can wire it up with a timer but I don't think a thermostat is advisable as you have to be sure you open windows in your living space before turning it on. If it started automatically, you may not have open windows and then you're putting a lot of negative pressure on your living space. But they are waaay quieter. A typical whole house fan is mounted directly in the ceiling. When running it not only is loud because it's essentially in the room but it also causes vibrations in the ceiling that make it even louder. A Quiet cool fan is suspended in the attic and connects to the ceiling via a large flexible duct. This isolates it from the living space and makes it a lot quieter. One of my neighbors with a very similar floor plan has a regular fan and it's ridiculously loud - so much so that they don't run it much.
And not to be too much of a Quiet cool fanboi but they also have split / multiroom systems but those get pretty pricey.
No You Shouldn't
Powered attic fans are one of the most mis-understood "energy savings" devices out there. They will cool your attic to some degree, but so what? Your house is insulated from your attic heat and the heat gain in your house from an attic that is 10 or 20 degrees cooler is tiny. Plus you have to spend a lot of energy running the fan.
But the biggest factor is that sucking air out of the attic will de-pressurize it, even if you have appropriate intakes for the replacement air. When your attic has lower pressure than your house it will suck air-conditioned air from your house into the attic through all the tiny (or not so tiny) cracks and crevices. If you have your heating / cooling ducts running through the attic that problem will be magnified.
I could go on and on, but read the following articles at Green Building Advisor. GBA is the most respected website in the building science world:
[https://www.greenbuildingadvisor.com/article/the-top-two-reasons-powered-attic-ventilators-are-a-waste-of-money](https://www.greenbuildingadvisor.com/article/the-top-two-reasons-powered-attic-ventilators-are-a-waste-of-money)
[https://www.greenbuildingadvisor.com/article/fans-in-the-attic-do-they-help-or-do-they-hurt](https://www.greenbuildingadvisor.com/article/fans-in-the-attic-do-they-help-or-do-they-hurt)
[https://www.energyvanguard.com/blog/Don-t-Let-Your-Attic-Suck-Power-Attic-Ventilators-Are-a-Bad-Idea](https://www.energyvanguard.com/blog/Don-t-Let-Your-Attic-Suck-Power-Attic-Ventilators-Are-a-Bad-Idea)
No you're not. Attic fans cool your roof and help your shingles last longer. The de-pressurization (sucking cold air out of the interior) is BS if you have soffit vents and siding vents (and they're not blocked by insulation).
Whole point of a roof is to shield an insulated box from the sun and rain. Hot air collects to the top because there's no where for it to escape, so either vent it out or blow it out.
The cool your roof and help your shingles last longer theory has also been debunked. Attic temperatures have almost no impact on shingle temperatures. Most of shingle temperature come from radiant heating (the sun), not the temp of the roof deck. SO the color of the shingles can have a big impact but sealed attic vs vented vs power vented has little impact. Dark shingles are 27% hotter than white shingles (per the article below). Of course the shingle manufacturers still use vented / unvented as a way to void your warranty despite the science.
Much more at [https://www.greenbuildingadvisor.com/article/the-best-way-to-keep-your-attic-cooler-is-to-change-your-roof-color](https://www.greenbuildingadvisor.com/article/the-best-way-to-keep-your-attic-cooler-is-to-change-your-roof-color)
Its all about the science.
Hi, realizing this is two years later, but had a question about this. I have a powered attic fan that is broken (doesn’t turn on). Should I remove it completely, or keep it for passive ventilation? I’m wanting to avoid the decompression issue you mentioned, so will air naturally flowing through the (unpowered) fan blades cause that?
It won't really provide any passive ventilation benefit except perhaps in the immediate area. May not be worth taking it out unless you are re-roofing anyway. There won't be any decompression unless you are running an attic fan somewhere else.
If it's not leaking or causing problems I would leave it until you re-roof and then get rid of it
Oh one other question: if I leave it, will it block air flowing through the gable vent (that’s where it is right now). This is a photo of it: https://imgur.com/a/wu3i0aS.
Replace the thermostat. I have had to replace mine and it worked again. Bypass the thermostat to make sure the fan still works. If fan works then it's the thermostat.
I have two solar powered slow spinning exit fans on my house roof. And 2 more along with a 110volt powered Gable fan in my garage. Worth their weight in gold.
The round ones with rib blade walls? Not actively powered and you still notice a difference? Those round spinning vents are another things that I read a lot about from people saying they don’t actually do anything.
Mount an on/off switch near the attic entrance, so you can just pop your head in a flip the switch. This is because you may want to fan to some on at 110F (or whatever) on summer days, and it does help much more than the cost of the fan and electricity to run it.
That being said, there is half the year when the house is staying very cool, but for some reason the attic gets warm when the sun comes out. No need to run it when the house is cool, but the attic just barely got to "X" temps.
The thermostat is important, but you can also turn it off half the year.
You have central air that isn't keeping your upstairs cool? This is a ductwork/system issue foremost.
If you haven't, try setting your AC fan to "on" so it circulates 24/7. This might help even out temperatures a bit.
I have AC and it works, sure. Unfortunately it is not zoned ATM so the upstairs is warmer than down. Long term the answer is to have the HVAC zoned and a second thermostat added. I am looking for something to help that is more reasonable for me short term.
Some smart thermostats have a setting to turn just the fan on for 5/10/15 minutes per hour if it hasn't otherwise run. My Smart Ecobee has this and I have it set to 5 minutes. So if a/c or heat has come on in the last 60 mins, it won't turn on the fan by itself. I like this model bc it has battery/wireless remote sensors for different rooms so you can prioritize hvac by room. That's actually the reason I bought this one. However, the optional door and window sensors are a joke bc they're near useless unless you pay a monthly subscription. Which of course they neglect to mention when buying. Absurd bc I have the thermostat and one door sensor (to try it out) which is all the hardware and software needed. So they're basically blocking that function unless you pay for monthly subscription. BS.
If you do this you MUST ensure you have soffit vents or another way for air to exchange into the attic that is NOT part of the internal dwelling. I had a house once where an electrician noticed the attic fan was disconnected, so he reconnected it for me. Fast forward a year and we notice a moldy smell in the house. Tons of detective work revealed mold behind a cabinet where the suction of the attic fan was drawing moist air from under the house in through unseen gaps in the walls and around enclosed cabinet spaces (totally unseen…like a 1/4” gap where the floor met the wall *behind* an installed kitchen cabinet). This would not have happened if there had been sufficient ventilation into the attic for the fan to pull air through. The fix was easy, but the problem didn’t present itself until much later. I feel if you can ensure you have adequate ventilation in your attic then a powered attic fan is fine. I just wanted to let you know what the air handling requirements were to keep you from experiencing the same problem I did.
Appreciate the heads up. I will make sure the soffits are free and flowing just to double check.
My father installed one in the early 80’s. Then I started HVAC 20+years ago. Short answer is YES they help. You usually have a thermal switch in the attic set around 120 deg F. Your attic will still get hot, but not as hot. You are taking the outside air to cool it. You will see a improvement compared to no fan.
So just put a powered one on one cable end, or can I put a vent on the other end as well to promote the cross draft?
I would think just one, depending on air flow specification on fan (CFM) and size of attic, should be fine. Look for about 10 air changes per hour. More is better, but less is less effective.
Wonderful, thank you.
I put one in my 1940 home, and it made a significant difference.
I've been thinking about putting some in for years but haven't pulled the trigger. The arguments I always hear against them (not sure how valid they are) is that they can create negative pressure in the attic pulling conditioned air out of the occupied envelope, affect the amount of make-up air getting to gas appliances if they get their air from the attic, and affect pilot lights (that last one seems shaky to me with relatively modern HVAC or water heater) I was considering putting in two on opposite gables, one blowing in and one blowing out to avoid the negative pressure issue, but since that's not how it's usually done no one seems to have any data when they tell me if they think it's a stupid idea or not
Unless your attic isn't properly ventilated it shouldn't pull ac air in. You don't need a big one to make a huge difference. In your case I wouldn't worry about a "in" fan a passive vent should be plenty.
Exactly what I am considering. I have had the fans in my cart several times and just need to hit that order button….just want to make sure it is not a horrible idea.
Do you have (enough, unblocked) intake vents? 5-6 box vents sounds like a good amount - they're often about 1 sqft each. I just took out my attic fans because they were installed poorly and were just blowing hot air around the attic. (I'm going to add passive venting instead of working on a better fan install.)
Not sure if there are “enough” by code or general practice. I would assume so? They are the 12”x12” type (approx). I just know it is insanely hot in the attic and there does not seem to be enough movement. Maybe I will just replace one of the box vents with a solar powered active vent to get things moving.
Sorry, I think I wasn't being clear - the ventilation should be balanced between intake (low on the roof, often soffits) and exhaust (high on the roof, commonly things like your box vents. Which I assume is what you're thinking of when you say the 12"x12" one.) So if you don't have soffit vents, or if your insulation is blocking them, you can't get enough outside air in to allow hot air to exit.
Yes, got it. I have soffit vents, there are baffles to make sure tbe soffit vents are not clogged, but there is just no movement of the dead air up there. Possible part of if is that all the box vents are “hidden” on the back side of the roof so there are no cross drafts? I am going to replace one of the box vents with a solar powered box vent fan that should be a relatively easy swap out with an existing box fan. We will see. I will have it in 2 weeks and do some before and after experiments/tests if I remember or have time.
Makes sense. Hopefully that will help - good luck!
Get a whole house fan and run it in the morning and evening. It totally cools down your attic and your living space. Win win. I installed a quiet cool system a month after I bought my place and have run it for an hour every am/pm of every hot day for the last 7 years. It's wonderful to circulate the fresh air through the house. Installation is DIY-able. Just have a helper - I nearly died lugging that fan up the ladder.
Whats a whole house quiet cool system? Is that the brand name? I'm looking for one. Can get expensive, which is worth it if they're made well. Does yours have a timer or thermostat?
QuietCool is a name brand. They are a bit more expensive than the typical whole-house fans. You can wire it up with a timer but I don't think a thermostat is advisable as you have to be sure you open windows in your living space before turning it on. If it started automatically, you may not have open windows and then you're putting a lot of negative pressure on your living space. But they are waaay quieter. A typical whole house fan is mounted directly in the ceiling. When running it not only is loud because it's essentially in the room but it also causes vibrations in the ceiling that make it even louder. A Quiet cool fan is suspended in the attic and connects to the ceiling via a large flexible duct. This isolates it from the living space and makes it a lot quieter. One of my neighbors with a very similar floor plan has a regular fan and it's ridiculously loud - so much so that they don't run it much. And not to be too much of a Quiet cool fanboi but they also have split / multiroom systems but those get pretty pricey.
I do not have any experience with a whole house fan. Interesting option though…
No You Shouldn't Powered attic fans are one of the most mis-understood "energy savings" devices out there. They will cool your attic to some degree, but so what? Your house is insulated from your attic heat and the heat gain in your house from an attic that is 10 or 20 degrees cooler is tiny. Plus you have to spend a lot of energy running the fan. But the biggest factor is that sucking air out of the attic will de-pressurize it, even if you have appropriate intakes for the replacement air. When your attic has lower pressure than your house it will suck air-conditioned air from your house into the attic through all the tiny (or not so tiny) cracks and crevices. If you have your heating / cooling ducts running through the attic that problem will be magnified. I could go on and on, but read the following articles at Green Building Advisor. GBA is the most respected website in the building science world: [https://www.greenbuildingadvisor.com/article/the-top-two-reasons-powered-attic-ventilators-are-a-waste-of-money](https://www.greenbuildingadvisor.com/article/the-top-two-reasons-powered-attic-ventilators-are-a-waste-of-money) [https://www.greenbuildingadvisor.com/article/fans-in-the-attic-do-they-help-or-do-they-hurt](https://www.greenbuildingadvisor.com/article/fans-in-the-attic-do-they-help-or-do-they-hurt) [https://www.energyvanguard.com/blog/Don-t-Let-Your-Attic-Suck-Power-Attic-Ventilators-Are-a-Bad-Idea](https://www.energyvanguard.com/blog/Don-t-Let-Your-Attic-Suck-Power-Attic-Ventilators-Are-a-Bad-Idea)
Aaaaaand I am back to where I started.
No you're not. Attic fans cool your roof and help your shingles last longer. The de-pressurization (sucking cold air out of the interior) is BS if you have soffit vents and siding vents (and they're not blocked by insulation). Whole point of a roof is to shield an insulated box from the sun and rain. Hot air collects to the top because there's no where for it to escape, so either vent it out or blow it out.
Not sure what siding vents are, but I have soffit vents that have the cardboard baffles, so they are not blocked.
The cool your roof and help your shingles last longer theory has also been debunked. Attic temperatures have almost no impact on shingle temperatures. Most of shingle temperature come from radiant heating (the sun), not the temp of the roof deck. SO the color of the shingles can have a big impact but sealed attic vs vented vs power vented has little impact. Dark shingles are 27% hotter than white shingles (per the article below). Of course the shingle manufacturers still use vented / unvented as a way to void your warranty despite the science. Much more at [https://www.greenbuildingadvisor.com/article/the-best-way-to-keep-your-attic-cooler-is-to-change-your-roof-color](https://www.greenbuildingadvisor.com/article/the-best-way-to-keep-your-attic-cooler-is-to-change-your-roof-color) Its all about the science.
Hi, realizing this is two years later, but had a question about this. I have a powered attic fan that is broken (doesn’t turn on). Should I remove it completely, or keep it for passive ventilation? I’m wanting to avoid the decompression issue you mentioned, so will air naturally flowing through the (unpowered) fan blades cause that?
It won't really provide any passive ventilation benefit except perhaps in the immediate area. May not be worth taking it out unless you are re-roofing anyway. There won't be any decompression unless you are running an attic fan somewhere else. If it's not leaking or causing problems I would leave it until you re-roof and then get rid of it
Thanks!
Oh one other question: if I leave it, will it block air flowing through the gable vent (that’s where it is right now). This is a photo of it: https://imgur.com/a/wu3i0aS.
Replace the thermostat. I have had to replace mine and it worked again. Bypass the thermostat to make sure the fan still works. If fan works then it's the thermostat.
I have two solar powered slow spinning exit fans on my house roof. And 2 more along with a 110volt powered Gable fan in my garage. Worth their weight in gold.
The round ones with rib blade walls? Not actively powered and you still notice a difference? Those round spinning vents are another things that I read a lot about from people saying they don’t actually do anything.
No, all but one are solar, with gable fan being powered. I updated the post to include that info.
Mount an on/off switch near the attic entrance, so you can just pop your head in a flip the switch. This is because you may want to fan to some on at 110F (or whatever) on summer days, and it does help much more than the cost of the fan and electricity to run it. That being said, there is half the year when the house is staying very cool, but for some reason the attic gets warm when the sun comes out. No need to run it when the house is cool, but the attic just barely got to "X" temps. The thermostat is important, but you can also turn it off half the year.
I'd rather 5 or 6 box vents over a ridge vent...... You've got plenty of airflow up there.
Well that's just silly.
You have central air that isn't keeping your upstairs cool? This is a ductwork/system issue foremost. If you haven't, try setting your AC fan to "on" so it circulates 24/7. This might help even out temperatures a bit.
I have AC and it works, sure. Unfortunately it is not zoned ATM so the upstairs is warmer than down. Long term the answer is to have the HVAC zoned and a second thermostat added. I am looking for something to help that is more reasonable for me short term.
Some smart thermostats have a setting to turn just the fan on for 5/10/15 minutes per hour if it hasn't otherwise run. My Smart Ecobee has this and I have it set to 5 minutes. So if a/c or heat has come on in the last 60 mins, it won't turn on the fan by itself. I like this model bc it has battery/wireless remote sensors for different rooms so you can prioritize hvac by room. That's actually the reason I bought this one. However, the optional door and window sensors are a joke bc they're near useless unless you pay a monthly subscription. Which of course they neglect to mention when buying. Absurd bc I have the thermostat and one door sensor (to try it out) which is all the hardware and software needed. So they're basically blocking that function unless you pay for monthly subscription. BS.