Solar Attic Fans vs Wired vs None

I just installed an electric gable vent fan in my shed. I wouldn't even bother with anything solar for that purpose out here. In the Summer it will run almost constantly from sunup to after sundown.

Anything solar just won't move enough air to make much of a difference. As always, YMMV depending on your location and Summertime temperatures.
 
Having worked in a lot of attics the ones with fans have always been much cooler. I know some guys will say they don't work or not worth the money but I am a firm believer.

If you are considering solar fans look at the ones made by quiet cool.
 
The cheapest and easiest way to keep an attic cool and by extension the house also is to insulate the attic heavily to an R38 at least. The roof deck needs to have venting of some sort, ridge vent or aluminum "cans"
The eves or overhangs (whatever you wish to call them) need to have baffles in them to create a void space along the bottom of the roof deck between the soffit and the attic space. The soffit also needs to have vents or perforated panels in order for cool air to enter.
This setup creates a continuous flow of air from the overhangs to the exit in the vents. It all happens passively and requires no power.
This setup also helps in cold climates by reducing or eliminating ice dams.
 
Having worked in a lot of attics the ones with fans have always been much cooler. I know some guys will say they don't work or not worth the money but I am a firm believer.

If you are considering solar fans look at the ones made by quiet cool.
They work, but the idea is not to have a cool attic, as that’s not where you spend your time, but to have cool rooms directly beneath it. Therefore properly done passive ventilation and lots of insulations is key and a much better solution long term.
 
Two main schools of thought

1. Powered attic ventilation is a total waste and only adds to your electric bill passive is the way to go. (owens corning) Dr Joe Lstibuerk.

2. Powered attic ventilation works well providing you move enough air and give it enough make up air which is more than you probably have. If you undersize the makeup air you will suck the cool air out of the house and go backwards.

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Building Science Corporation has a ton of free information available. Dr. Lstibuerk is also an influential member of the code council.
 
I have evaporative cooling in my garage, (3 car attached). I also have upduct discharge into the attic. This keeps the attic very cool when it's running. If I didn't have that, I would for certain have at least one gable fan installed to pull fresh air through it.

There is no downside to having fresh air pulled through your attic when the outside temperatures are well into the 3 digit range.
 
In FL we are lucky to keep our house at 76* during the summer. If the attic fan was set to 76* of 72* it would run 24/7/365 in FL. My attic probably easily hits a buck twenty during the summer.
I think that SubierubyRoo was referring to outdoor environmental temperatures when citing 80 degrees F and 76 degrees F as the fan on/off temperature.

The corresponding attic temperature would typically be 25 - 30 degrees F higher (i.e., ~110 degrees F) on a sunny day.
 
My S. FL house has a white concrete barrel tile roof and 2 solar attic fans. The combo is epic and the attic remains at ambient temps. 2.5 ton AC can maintain 70ºF all summer long, 2500 sq ft. The 5 ton compressor only kicks on if temp rises 2º. Which only happens if I turn the temp up while at work.

My prev house had gray shingles and the attic reached 140ºF in the FL summer. Despite ventilation, that heat would radiate down through the R19 fiberglass insulation and heat up the house. We could easily feel the heat radiating. The 3ton AC could not keep up and cool a 1150 sq ft house.
 
After much consideration we decided to go with ridge vents and looking into upgrading our soffit ventilation (if needed). Roofer said the fans will not make a huge difference.
I tend towards roof venting without power but Im not sure if you ever stated whether your HVAC system and vents are in the attic.
If not then it's a no brainer to insulate and plenty of roof vents.

But the question becomes dicey if your system is up there and not under the house. I know, I asked myself that for 16 years as mine was in the attic, two HVAC units and all the ductwork. I never did a power fan and since the home was new 16 years ago venting was adequate but it does get hot up there. 110 to 120 not our of the question.

Anyway, that was then, just sold that house but now moving to a smaller home with the same thing, HVAC unit (one) is in the attic.

On the new house there are a total of 12 vents at the top, 4 vent on each of 3 sides. None facing the street. It could be as little as 10 vents. I cant confirm since I didnt take a photo of the side, so for some reason I think it can be as little as 3 or maybe the same as the back with 4 on the sides.
This is our home under construction, soon to close.
Screenshot 2023-03-08 at 9.00.11 AM.jpeg
 
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I tend towards roof venting without power but Im not sure if you ever stated whether your HVAC system and vents are in the attic.
If not then it's a no brainer to insulate and plenty of roof vents.

But the question becomes dicey if your system is up there and not under the house. I know, I asked myself that for 16 years as mine was in the attic, two HVAC units and all the ductwork. I never did a power fan and since the home was new 16 years ago venting was adequate but it does get hot up there. 110 to 120 not our of the question.

Anyway, that was then, just sold that house but now moving to a smaller home with the same thing, HVAC unit (one) is in the attic.

On the new house there are a total of 12 vents at the top, 4 vent on each of 3 sides. None facing the street. It could be as little as 10 vents. I cant confirm since I didnt take a photo of the side, so for some reason I think it can be as little as 3 or maybe the same as the back with 4 on the sides.
This is our home under construction, soon to close.
View attachment 143867

That’s the problem with having your hvac in the attic. At the very best you could bring that space to the ambient temperatures, which would still be way higher than optimal. Or lower than optimal during winter. Passive or active venting will make minimal impact IMO.
At best you can hope your builder insulated the vent lines and sealed them properly. That’s about it.
 
That’s the problem with having your hvac in the attic. At the very best you could bring that space to the ambient temperatures, which would still be way higher than optimal. Or lower than optimal during winter. Passive or active venting will make minimal impact IMO.
At best you can hope your builder insulated the vent lines and sealed them properly. That’s about it.
Well, building code is for R-9 in flex duct. Im not really concerned I like to analyze and look for simple improvements if reasonably possible.
Agree, passive or active venting will be minimal in a new home as long as the passive is robust, new building codes pretty much cover that. Furthermore if you go active in an attic with ridge vents or any kind of vents. Air flows with least resistance and will tend to short cut from the vents to the fan vs up the soffit vents and out the roof fan.

Tough question though depending on design of home. Meaning in a home with, let's say, cathedral ceilings into what would have been the attic, forcefully pulling air between the roof rafters and the ceiling insulation may help, IF the air isnt taking a short cut from the ridge vents or any other venting which leads me back to typing too much once again *LOL* I agree... in a proper up to date home with the latest building codes passive is fine.

Having HVAC units in attics is not ideal by any means but a fact of life with many production builder homes and almost always now that some many are pouring slabs instead of crawl spaces.

@KrisZ
Not the best shot, 16 years ago I took this photo while it was under construction. Big deal to me at the time, there are two condenser units up there. One for the first level and one for the second. Photo is only showing half of the mass of flex duct. Not ideal being up there in the south but that is what they do. When the AC would kick on you cold feel the HOT blast of air it faded quickly though.
HPIM2554_original copy.jpg
 
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I tend towards roof venting without power but Im not sure if you ever stated whether your HVAC system and vents are in the attic.
If not then it's a no brainer to insulate and plenty of roof vents.

But the question becomes dicey if your system is up there and not under the house. I know, I asked myself that for 16 years as mine was in the attic, two HVAC units and all the ductwork. I never did a power fan and since the home was new 16 years ago venting was adequate but it does get hot up there. 110 to 120 not our of the question.

Anyway, that was then, just sold that house but now moving to a smaller home with the same thing, HVAC unit (one) is in the attic.

On the new house there are a total of 12 vents at the top, 4 vent on each of 3 sides. None facing the street. It could be as little as 10 vents. I cant confirm since I didnt take a photo of the side, so for some reason I think it can be as little as 3 or maybe the same as the back with 4 on the sides.
This is our home under construction, soon to close.
View attachment 143867
We don't have the air handler in the attic. Those look like off ridge vents, my roofer said they aren't to code anymore. Maybe that is just in my area.

Furthermore if you go active in an attic with ridge vents or any kind of vents. Air flows with least resistance and will tend to short cut from the vents to the fan vs up the soffit vents and out the roof fan.
This.
 
@alarmguy yes that’s what I have too. I don’t like it. It’s the lazy and cheap way of doing this. Here is part of the mess at my house, you can’t really take a good picture of the whole thing.

Although the plywood on my roof is lined with a reflective tape, you can see the structure reflecting off of it. Not sure if it helps anything. This type of reflective tape is good for reflecting radiant or infrared heat. So it would trap it inside?
I think it should’ve been pointed outward not inward. Ah, the joys of home ownership😂

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Whatever your plan is, it has merit. Insulation is designed to keep the temperature in the house as constant as possible. Once heat passes upwards into the attic, it needs to be removed. If heat enters the attic from insolation, it needs to be removed ASAP so that it doesn’t migrate into the living space. This keeps the lumber, and ultimately the roofing (especially shingles) cooler, and will extend the lifespan in addition to reducing HVAC run time.

Whether wired or solar, you want enough airflow to exchange the air pretty frequently, probably once every 5 mins or so. Ridge vents appear convenient, but if you don’t have them they require a bunch of work to install, and are a downgrade in structural integrity of the roof as a whole IMO. Powered gable vents are the best option IMO because you’re not creating additional leakage points by adding sufficient venting to circulate the attic air. 👍🏻
 
We don't have the air handler in the attic. Those look like off ridge vents, my roofer said they aren't to code anymore. Maybe that is just in my area.


This.
If your roofer is correct it must be a Florida state only code. The is a brand new build in North Carolina, in fact, just got its final inspection and C/O in the last 7 days.
Common in in other states. :)

Being you dont have the air handler in the attic, I would be inclined as you are thinking. Just make sure it's properly vented and PLENTY of insulation.
 
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