Solar Attic Fans vs Wired vs None

I wouldn’t, as insulation is the best solution for this problem, but many install the attic fan as a band aid solution. Maybe it’s more profitable for the contractors?
Well, insulation and proper ventilation is key. The OP doesnt state if his HVAC system and duct work are in the attic.
If so and if there are Gable vents, which I assume there are since he says he could put a gable fan in, putting a fan in one would make sense or just center of the house and air would be drawn in from the gable vents..and out through the roof fan.
I would look at that as the most efficient use of the fan since you are cutting a large hole in the roof you will have passive cooling until the sun heats the roof up to a point where the fans turns on.

Once could also again, (assuming do to lack of information) if the house has gable vents and soffit intake vents if he doesnt go the fan route in the center of the roof he could just have standard static roof vents installed for more air circulation. At that point though, I rather have one big hole in the roof with an electric back up fan for those hot days.
 
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Make sure you have enough square feet of attic ventilation and insulation and maybe reflective insulation. I doubled my attic vent area in my house when I lived in Palo Cedro Calif [it gets hotter that Hades there in the summer and I actually like the heat] and when cutting the vent area for the roof ridge vents, the hot air comming from the vent cuts was amazing.
 
If there aren’t ridge vents but there are gable end vents a fan mounted in the gable end vent is more effective than a roof mount. It is larger and moves more hot air out of the house.
 
Main objective is to help cool the house and decrease load on the A/C during the hot season.

Agendas aside, when I look at the numbers they tell the truth. Solar fans get about 300-500 CFM (maybe). Hard wired get 1200(+) CFM. I could also do gable mount fans. The price of solar is much higher, I don't know if I could offset the higher price with power saving. I mean how much power do fans actually use? Then I started thinking....

Lets put our math hats on...

Read online 1.65A per fan...

1.65A x 120V = 198W, lets just say 200W per fan.

So if I got 3 fans = 600W

My power company charges ~$0.15 per 1KWH (1 hour use of 1000 watts).

So if 1000W = $0.15, then 600W = $0.15 X 0.6KWH = $.09

I am probably looking at less than $0.09/day to run them. I am sure they would run less than 1 hour a day even during the hottest season.

$0.09 x 270 days = $24.30 rough yearly operating cost. Not 365 days because I am also accounting for winter.

How many years to offset the higher price of solar fans? 🤔🤔🤔

Solar fans were quoted to be several thousand dollars... :sick:

I also could just leave the static ventilation.

I am old school. Show me the data kind of guy. Similar to most BITOG members. Would love to hear your thoughts.

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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I would suggest if you really think your attic fan only needs to run an hour then you dont need one.
I used to have a mid output electric attic fan in a northern climate. I think set to come on around 110 degrees, (grabbing at straws with that number) and it would run from about 3Pm to 9ish pm in the summertime.
Agree and same with my experience. I had just a basic fan I picked up at Home Depot and set at 105F (I think, its been a couple years since we moved from that house) it ran from mid-morning to an hour or so before sunset all summer long.

It did pump out some serious hot air, I could be up in the attic on a warm sunny day and sure it was warm, but plenty tolerable. Without the fan running, it was 1-2 minutes at most and I'd be dying and drenched in sweat.

On the positive side, it did very noticeably decrease our 2nd floor bedroom temperatures, which was the reason I put it up there to begin with. That house wasnt insulated very well, and I knew we werent going to be staying in this house for too long so I didnt want to invest a bunch of money and time in insulating it, but a fan was cheap and easy. And it did definitely help.
 
I read SOMEWHERE that attic fans are of no use in Florida. Ridge vents should be sufficient if adequate perforated soffit is being used for air intake.
That being said, I have heard of two things that DO work in Florida. Foil faced foam boards attached to the 2X4's UNDER the roof, foil facing out, air space and venting in the space between.
And Spray foam under the roof sheathing. This one I heard from a contractor that has installed it on his own home. He said it keeps the air ducts cool as well (in the attic) and allowed him to put an A/C vent into the space.
I can't see where the A/C vent makes much sense, nor what it would add to your annual cost.
I also don't know what impact either of these methods would have on the longevity of the shingles on the roof. Metal or tile roofs would not be impacted of course.
Personally, I'd prefer the foil faced boards. No ongoing electricity use at all.
 
I repurposed an old dilapidated shed into a workshop. All the interior wood had aged to a dark brown, and the termites holding hands were a structural component.

Their poop could also fall from roof and affect a project atop my table, so I stapled some cheap plastic drop cloth bridging the bottom of the rafters to prevent termite ball bearings from hitting my table.

The portion of the roof not covered by black plastic, standing under it in direct sun, I was able to feel the increased radiation, compared to that under the plastic.

In a hot spell, I decided to both a weak low wattage quiet 120mm computer fan, AND a a powerful variable speed 140mm computer fan to exhaust the apex of the roof, and at 3PM turning it on high for first time, I was expecting results, which did not come to fruition. It did not seem to lower the temps inside much at all.

But the next day, with the weak fan running overnight and as the sun rose, the interior wood did not get as hot and the interior stayed noticeably cooler throughout the afternoon, and then cooled off faster late afternoon. The more powerful fan turned on high could help evacuate the air inside once I opened the door, but having it on with teh weaker fan overnight did not noticeably keep it cooler if I opened the door early afternoon.

The SW facing wall, once the sun would start baking on it, the blackened well aged wood, would radiate heat onto my table and face. As the interior was so dang dark as well, I got some white drywall primer, as it is the cheapest i could find, and rolled it on thick, to half the offending west facing wall, twice.

Come that afternoon, with the sun beating on that wall, the area painted white radiated significantly less heat onto my table. My IR gun was showing 14 less degrees on the wall itself, and the portion of the work table behind white painted wall was 6.5f less than the portion of table adjacent to it behind the bare dark wood. Also my interior lights were way more effective.

When i painted the whole west facing wall with the drywall primer, and kept at least one weak 57cfm fan running 24/7, and could turn on the other exhaust fan @ ~ 250cfm midday, the shed went from intolerably hot, to being able to work inside on the hottest afternoons without issue.

Obviously a real radiant barrier, like reflectix, stapled between rafters/studs on roof and west facing walls( the east wall was largely shaded and had plywood and shelves on the studs) would have far better results, but the can of white drywall primer significantly reduced the emissivity of the heat radiating surfaces, and cost me far less than a dedicated radiant barrier with the added benefit of improving interior lighting.


White paint itself has no R value, but it will significantly reduce the emissivity of a hot surface and reduce the amount of heat radiated from it, very noticeably so, to a human standing under it.

I'm now in SW Florida, and have been climbing around in the attic of parents home a bit. The Hvac insulated ducting is ~40 years old, most of it. It is dark grey. Some newer return vents have been replaced with highly reflective insulated ducting, but I found the installers did a poor job, and the joints taped poorly and one, Not at all. Can look down at it and see into the home interior!

The HVAC system is able to suck in hot attic air in several points. Also, some of the bigger ducting is resting unsupported across a beam seriously constricting the flow, in many areas.
I see so much room for improvement, and will soon be spending time up there addressing the ducting's shortcomings, as obviously the original builders did not much care, and whoever worked on it in the ~40 years since did not much care either. The home's interior, some rooms are nice and cool, and others seemingly devoid of AC completely. One of those being the guest room, which I now inhabit.
 
Agree and same with my experience. I had just a basic fan I picked up at Home Depot and set at 105F (I think, its been a couple years since we moved from that house) it ran from mid-morning to an hour or so before sunset all summer long.

It did pump out some serious hot air, I could be up in the attic on a warm sunny day and sure it was warm, but plenty tolerable. Without the fan running, it was 1-2 minutes at most and I'd be dying and drenched in sweat.

On the positive side, it did very noticeably decrease our 2nd floor bedroom temperatures, which was the reason I put it up there to begin with. That house wasnt insulated very well, and I knew we werent going to be staying in this house for too long so I didnt want to invest a bunch of money and time in insulating it, but a fan was cheap and easy. And it did definitely help.
Actually I did mine for the same reason. The second floor had (lack of better word) cantilever ceiling meaning most of the way up sheetrock was screwed into the roof joists and limited room for more than 1950s thick insulation of a few inches. Only a small area up top where the ceiling was flat I was able to add 12 inches.
So I opened up the soffits which was siding over closed up boards, ran insulation along the roof joists, also had two ok sized gable vents and added the power vent.
 
I do like those but unfortunately our area gets high winds and those are not a good option.






Balderdash!!

The combination of those fans with proper soffit and gable vents Is a proven method.

High winds enough to damage them would damage your whole roof/house first.

Where is your AC installed? Do you have any area of vaulted/cathedral ceilings?

Adequate insulation?
 
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I am sure they would run less than 1 hour a day even during the hottest season.

This seems like a generous assumption. If true, the ventilation must already be excellent.

I rent a 1200 sf ranch in Central Virginia. With the thermostat set somewhere above 100, it kicks on around mid-late morning starting in March. In the summer, it is still running when I go to bed. I think there are not enough soffit vents--2, or at most 3 on either side.

The stupid thing is so worn out that it rattles like crazy and sends vibrations all through the house. It's mounted on the south end, and I could hear it rattling away while I was in bed on the north end. Several years ago, I just started to shut it off at the breaker.

The roof was replaced a few years ago, and a ridge vent was added. That seems to have made the attic considerably cooler. Oddly enough, the water heater pilot light used to go out in really hot weather, but that hasn't happened since the roof replacement. (WH and HVAC are in the attic.)
 
A lot of good ideas here. Insulation is good. AC is in the house. Soffit ventilation may not be adequate. Run time on the fans may have been underestimated. The more I think about it the more inclined I am to take the old man route and just leave it alone lol.
 
When I built my home I did not have an attic fan. After one summer of heat on the second floor I installed one attic fan. I could not believe the difference. They make a real difference in second floor cooling.
 
Main objective is to help cool the house and decrease load on the A/C during the hot season.

Agendas aside, when I look at the numbers they tell the truth. Solar fans get about 300-500 CFM (maybe). Hard wired get 1200(+) CFM. I could also do gable mount fans. The price of solar is much higher, I don't know if I could offset the higher price with power saving. I mean how much power do fans actually use? Then I started thinking....

Lets put our math hats on...

Read online 1.65A per fan...

1.65A x 120V = 198W, lets just say 200W per fan.

So if I got 3 fans = 600W

My power company charges ~$0.15 per 1KWH (1 hour use of 1000 watts).

So if 1000W = $0.15, then 600W = $0.15 X 0.6KWH = $.09

I am probably looking at less than $0.09/day to run them. I am sure they would run less than 1 hour a day even during the hottest season.

$0.09 x 270 days = $24.30 rough yearly operating cost. Not 365 days because I am also accounting for winter.

How many years to offset the higher price of solar fans? 🤔🤔🤔

Solar fans were quoted to be several thousand dollars... :sick:

I also could just leave the static ventilation.

I am old school. Show me the data kind of guy. Similar to most BITOG members. Would love to hear your thoughts.
I think your estimate of runtime is low. Most attic fans I’ve seen and used over the years turn on at 80*F and don’t shut off until like 76* or 72*. No matter if heat comes up through insulation or into attic from sunshine/ambient temps, the proper way to deal with it is to move that attic air out and reduce the temps. You’re trying to reduce as much temp transfer into the house as possible!

Good luck 👍🏻
 
I think your estimate of runtime is low. Most attic fans I’ve seen and used over the years turn on at 80*F and don’t shut off until like 76* or 72*.

The two that I've seen and used had an adjustable thermostat. If an attic fan was set to turn on at 80F and didn't shut off till 76F..it would probably run 24 hours a day here in the summer. An attic fan is just wasting energy if it continues to run once the temp inside the attic is the same as outside.
 
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.
 
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