Experience with solar powered roof fan to bring down attic heat?

1,912 Views | 26 Replies | Last: 2 yr ago by FatZilla
Ag13
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AG
Looking to have one installed in Houston. Our third floor is basically a finished out attic space. When the sun is out and temp is 90 or above, its hard to get the a/c below 80 degrees. Have had a/c checked multiple times and it's operating properly. Also, when the sun is down, no problem getting the room cold.

I have also had the insulation checked and there were no obvious issues or gaps.

The surrounding attic just seems to be too hot (have measured at 140+ during the day) which is why I'm thinking a roof fan may help. Had a quote for $1,300 and this would also include beefing up the insulation. If the A/C is left off all day, the room can easily get into the 100's - even at night.

Any experiences with this? Most important to me would be to actually get the room temp down as I will be working there for the foreseeable future (thanks covid). Of secondary importance is energy savings to somewhat recoup the cost eventually.

The installer that gave me the quote says it can bring the attic temp down about 20 degrees which, it seems, would help a ton.

Edit to add: This is what the makeup basically looks like. Other than the already installed soffit vents, there appears to be zero ventilation whatsoever out of the attic. My understanding of the fan is that it will help pull the cooler air through the soffit vents


MGS
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Texker
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AG
I looked into an attic fan at one point and decided against it because I wasn't confident in the efficacy.

Our current home has a radiant barrier(already installed when we bought it) and I have to say relative to our previous house the attic is significantly cooler. We have the turbine vents as well but if I had installed the roof I would have gone with a ridge vent.
Birddog
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AG
When we bought our house had two non solar ones. After first summer they died. I did research and came to conclusion they were not very effective so I didn't replace them and eventually went with ridge vents. They can suck air out of the conditioned house as well. This is a popular subject on here so I bet you could dig up some old threads.
JP76
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How is this currently cooled ?


Via central hvac ?


Is it a zoned unit ?



Is there the maximum amount of ridge vent on that upper ridge already ?


I would not install an attic fan unless you are 100% sure there is at least 1 1/2 inches of air flow space between the decking and the top of the insulation where the rafters are.


Even then it will probably try to pull conditioned air out of the room.

Easiest and cheapest solution is to increase your cooling via window unit or stand alone portable ac unit. This is a $400 max cost solution with that route.
TMoney2007
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AG
What kind of insulation is there around the 3rd floor room?
ABATTBQ11
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AG
What kind of gaps exist between the soffit vents and the peak of the roof? It seems like the walls of the room cut off airflow between the lower attic space with the soffits and the upper attic space.

You do need some kind of exit point, whether a fan, ridge vent or just a static vent. Convection should naturally ventilate the attic space with adequate openings at the top and bottom, with hot air rising out of the upper openings and cooler outside air flowing in from the bottom to replace it. Fans are typically used to boost ventilation if you can't get enough cooling from natural convection.

If your walls block airflow from the bottom attic space to the top, or if there isn't enough open space for air to flow through, no vent or fan up top will help. You need to make sure you have a large enough cross section of open space between attic spaces to move air from one to the other.



ETA Even if an attic fan pulled some conditioned air out of the room, it wouldn't be that bad. If the attic temperature around the room is 140*, then losing some conditioned room air is probably an acceptable loss if OP can bring that down 20* or so by ventilating. Even pulling some air out of the room attacks the real problem of the overheated attic. He'll never get the room cool with that kind off temperature difference.
water turkey
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We just had one installed. I took the temperature in the attic today. 115 degrees. Outside temp was 98.
Ag13
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AG
JP76 said:

How is this currently cooled ?


Via central hvac ?


Is it a zoned unit ?



Is there the maximum amount of ridge vent on that upper ridge already ?


I would not install an attic fan unless you are 100% sure there is at least 1 1/2 inches of air flow space between the decking and the top of the insulation where the rafters are.


Even then it will probably try to pull conditioned air out of the room.

Easiest and cheapest solution is to increase your cooling via window unit or stand alone portable ac unit. This is a $400 max cost solution with that route.


Central AVAC. Zoned in the sense that the third floor has it's own unit. It's one big room on the third floor so no need for zoning beyond that.

I don't believe there is a ridge vent on the top

I've thought about possibly adding a window unit but worried that it's going to result in the same issue I am already having. As mentioned the current A/C works fine (per a/c repairman) and it's a relatively small room that is the solo recipient of the unit's air.
Ag13
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AG
TMoney2007 said:

What kind of insulation is there around the 3rd floor room?


There is both the padded insulation packets (not sure of correct term) and spray on
Ag13
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AG
water turkey said:

We just had one installed. I took the temperature in the attic today. 115 degrees. Outside temp was 98.


Any chance you took the temperature in the attic before having it installed? Were you having the same issue as me or was it purely to get the attic temp down? Thank you

And appreciate all the responses
lunchbox
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JP76 said:

How is this currently cooled ?


Via central hvac ?


Is it a zoned unit ?



Is there the maximum amount of ridge vent on that upper ridge already ?


I would not install an attic fan unless you are 100% sure there is at least 1 1/2 inches of air flow space between the decking and the top of the insulation where the rafters are.


Even then it will probably try to pull conditioned air out of the room.

Easiest and cheapest solution is to increase your cooling via window unit or stand alone portable ac unit. This is a $400 max cost solution with that route.
Just wanted to highlight what this poster said. If your openings for lights/vents/fans/etc aren't properly sealed, the fan will pull the cooler air from your home into the attic.
water turkey
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Unfortunately, I did not take the temperature before but assume it would have been at least 130 degrees on a day like today.

FatZilla
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AG
Instead of insulating the attic or venting it more, you could have the walls on the room spray foamed (outer side of interior box's walls) and some extra batting put around any vent/fixture that can let air out. I would focus on keeping the cold air inside the room cool rather than trying to get the attic cooler.
ABATTBQ11
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FatZilla said:

Instead of insulating the attic or venting it more, you could have the walls on the room spray foamed (outer side of interior box's walls) and some extra batting put around any vent/fixture that can let air out. I would focus on keeping the cold air inside the room cool rather than trying to get the attic cooler.


He already has it insulated with batts and spray on. Problem is the temperature delta. If the attic is 140, there's no way you're keeping the room it surrounds in the 70's. You're looking at a 60+ degree delta. That's like keeping your house in the 40's. You'd need to insulate like a freezer.
Waltonloads08
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AG
Ive heard many mixed reviews. some houses it helps, others it doesn't. lots of variables.
Builder93
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AG
If you don't have a ridge vent, you need to install that first. No question. The solar fan will lower you temps if you have no ventilation at the top of the roof no doubt. Any hole will help, but the ridge vent is the most important thing. And it doesn't have any mechanical parts to break down.
evan_aggie
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AG
I installed this powered model myself:
https://www.homedepot.com/p/Master-Flow-1000-CFM-Mill-Power-Roof-Mount-Attic-Fan-ERV4M/205924928

We live in a 1949 home with 3 gable vents, which give us something like 500-600 sq inches of potential intake. We did not have soffits. We also did not have ridge vents or even old-school turbines! I would do a lot of work in the attic and I measured temps up to 145. After installing this fan, they came down to 120-125.

I debated often about whether to go solar, because after all, running the fan costs electricity. However, do the math on 150-200W motor depending on which model you pick and the runtime in the summer. I think it is really hard to justify the cost of solar vs this $100 model.

They will tell you that you don't need an attic fan if you have functioning soffits + ridge, but I'm not sure if that is always true.
JP76
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evan_aggie said:

I installed this powered model myself:
https://www.homedepot.com/p/Master-Flow-1000-CFM-Mill-Power-Roof-Mount-Attic-Fan-ERV4M/205924928

We live in a 1949 home with 3 gable vents, which give us something like 500-600 sq inches of potential intake. We did not have soffits. We also did not have ridge vents or even old-school turbines! I would do a lot of work in the attic and I measured temps up to 145. After installing this fan, they came down to 120-125.

I debated often about whether to go solar, because after all, running the fan costs electricity. However, do the math on 150-200W motor depending on which model you pick and the runtime in the summer. I think it is really hard to justify the cost of solar vs this $100 model.

They will tell you that you don't need an attic fan if you have functioning soffits + ridge, but I'm not sure if that is always true.


So only pulls 3 amps or less ?


What do you have the thermostat set on to come on ?
evan_aggie
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AG
1.35A if you believe the mfg specs.

I've been playing with the thermostat some. I had it set to 105 and then lowered to 95 but that basically means it runs from 10 or 11am to 10pm. So I'll probably set back to 105.
Builder93
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AG
evan_aggie said:

I installed this powered model myself:
https://www.homedepot.com/p/Master-Flow-1000-CFM-Mill-Power-Roof-Mount-Attic-Fan-ERV4M/205924928

We live in a 1949 home with 3 gable vents, which give us something like 500-600 sq inches of potential intake. We did not have soffits. We also did not have ridge vents or even old-school turbines! I would do a lot of work in the attic and I measured temps up to 145. After installing this fan, they came down to 120-125.

I debated often about whether to go solar, because after all, running the fan costs electricity. However, do the math on 150-200W motor depending on which model you pick and the runtime in the summer. I think it is really hard to justify the cost of solar vs this $100 model.

They will tell you that you don't need an attic fan if you have functioning soffits + ridge, but I'm not sure if that is always true.
This is true if your ratio between the 2 are correct and the attic is designed correctly.
armymom
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We had two solar powered fans installed last fall when we got new insulation and a HVAC. We have a tall attic and it has made a difference for the better. Even our garage when closed seems to not be as hot. Before installation we had to open the attic door and garage side door for ventilation because of the heat. Don't have to do that now!
PincheDriller
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AG
Same we have a steep roof and when I got my roof replaced I added a solar attic fan, as well as fixing any ridge vents. Attic temps dropped 20degs and upstairs AC doesn't struggle like before.
Aggietaco
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AG
Builder93 said:

evan_aggie said:

I installed this powered model myself:
https://www.homedepot.com/p/Master-Flow-1000-CFM-Mill-Power-Roof-Mount-Attic-Fan-ERV4M/205924928

We live in a 1949 home with 3 gable vents, which give us something like 500-600 sq inches of potential intake. We did not have soffits. We also did not have ridge vents or even old-school turbines! I would do a lot of work in the attic and I measured temps up to 145. After installing this fan, they came down to 120-125.

I debated often about whether to go solar, because after all, running the fan costs electricity. However, do the math on 150-200W motor depending on which model you pick and the runtime in the summer. I think it is really hard to justify the cost of solar vs this $100 model.

They will tell you that you don't need an attic fan if you have functioning soffits + ridge, but I'm not sure if that is always true.
This is true if your ratio between the 2 are correct and the attic is designed correctly.
I like how even the fan mfr doesn't recommend the fan.

From the HD product page images:

ABATTBQ11
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AG
Where do they not recommend a fan? Only the gable fan isn't recommended for any design. Fans are recommended for hip roofs that lack the ridge length for a suitable ridge vent.
Aggietaco
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AG
ABATTBQ11 said:

Where do they not recommend a fan? Only the gable fan isn't recommended for any design. Fans are recommended for hip roofs that lack the ridge length for a suitable ridge vent.
They are "suitable" but not "recommended".

ETA - for a gable roof anyway, wasn't looking at hip.
Ag13
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AG
So I sincerely appreciate all the replies. I have not decided whether or not I am going to get the attic fan yet, because I have used some of the feedback on here to investigate another problem - air leakage.

I bought a cheap blue tooth thermometer that I have been keeping in the attic to view the effect of different things and despite it being 95 degrees + outside the attic has only been getting up to a max of around 115 degrees so not a HUGE delta inside the attic vs outside air. When the A/C guys came out and measured 140 degrees they were using an infrared gun thermometer and my assumption is that the objects in the attic they were pointing at are just a lot hotter than the air my thermometer is measuring.

There are a few obvious issues with air leakage now that I am looking for it. The first is a door that leads into the attic room where our hot water heater is. Not only is this door very thin, there is also a relatively large gap between the bottom and the floor. When I step inside the door and shut it, I can feel cool air rushing in at the bottom and can even hear the wind sound.



Yesterday, with similar outdoor temps as prior testing days, I jammed a blanket underneath the door and "sealed" the bottom as best I could. The air conditioner was able to get the room at 78 (was set at 73), but still an improvement from not being able to come below 80. The temperatures in the attic seemed to be about the same. I am planning on buying a more robust draft stopper for the bottom of the door and applying insulation tape to the sides to really lock this door down. I may also apply some insulation board to the inside of the door - as I mentioned it's a thin door and during the day it is very warm to the touch.

Second, we have an attic hatch that has giant holes in it. First picture is view from outside and second picture is view from inside.



As you can see, a ton of light is getting in, so it seems logical that a lot of air is seeping through hear. You can once also hear air whistling in from inside when the hatch is shut. This is a metal hatch, so like the door, it is hot to the touch. I am having trouble coming up with a way to seal this one off. I don't think insulation tape from the inside/in the gaps will be very effective as gravity will cause it to lose it's air tight seal. I think that applying insulated tape from the outside would do the trick, but, this is not very slightly and it would have to be re applied every time the attic door actually needs to be opened. Any thoughts on this? I do plan on putting insulation board on the door itself to help try and cool down the hatch, but, that still leaves the big gaps.
FatZilla
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AG
Ag13 said:




As you can see, a ton of light is getting in, so it seems logical that a lot of air is seeping through hear. You can once also hear air whistling in from inside when the hatch is shut. This is a metal hatch, so like the door, it is hot to the touch. I am having trouble coming up with a way to seal this one off. I don't think insulation tape from the inside/in the gaps will be very effective as gravity will cause it to lose it's air tight seal. I think that applying insulated tape from the outside would do the trick, but, this is not very slightly and it would have to be re applied every time the attic door actually needs to be opened. Any thoughts on this? I do plan on putting insulation board on the door itself to help try and cool down the hatch, but, that still leaves the big gaps.
For the inside to help with heat blockage and air flow. Staple this to your flooring above and seal around it with calk. It is larger than you need i think but i couldn't find a square one.
https://www.amazon.com/Energy-Wise-Attic-Stairway-Cover/dp/B077NFG7DH

to seal it even better, a magnetic vent cover if you can find 1 big enough for the entire hatch, if not, individual ones on each seam to block air flow.
https://www.amazon.com/XFasten-Magnetic-Industrial-Magnets-Sidewall/dp/B0756RJFB6/
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