June 18, 2016

Solar Attic Fan

Last summer I blogged about "Living Without Air Conditioning," and had quite a few comments about the benefit of attic vent fans. This summer we decided to put one in.


The intent of the attic vent fan is to vent the hot air which stacks up in the attic and transfers its heat to the rest of the house. In order for this to work, it must be able to draw enough fresh air from the outside to properly vent the hot air. It can do this with gable, soffit, and/or ridge vents. Otherwise it can actually depressurize the attic and pull up air from inside the house (which can make an air conditioner work overtime and draw fumes from things like gas water heaters).

There are two types of attic vent fans, those that are installed in the roof, and those which are installed in a gable end of the attic. Neither Dan nor I was too keen on cutting a hole in the roof, and since we have gable vents on all the gables we opted for a solar gable fan.


Installation was very easy.

First step was to remove the old vent cover.

The fan was slightly wider than the vent opening, so a
little cutting with the jig saw was all that was needed.

Scraps filled the gaps and hardware cloth covers the fan so that things
like bats, snakes, or squirrels can't move in. We still need a new vent cover.

The solar panel went on top of the roof. Dan ran the cord through the
opening that was already there for flood lights (which are disconnected).

This one came with a pre-installed thermostat so that the fan kicks on when the attic temperature reaches 85°F (29°C). It is easy to remove or replace with a programmable thermostat. The fan runs whenever the daylight is bright enough to power the fan (it doesn't necessarily need the sun). It picks up speed and vents fastest when the sun is overhead.

How well does it work? Last Tuesday was our hottest day so far this year.

The top number is the outside temperature, bottom
is inside (kitchen, warmest room in the house).

The high was 99°F (37°C) outside, while inside it was a "tolerable" 84°F (29°C). Some folks may argue the "tolerability" of 84° for an inside temperature, however, there is something to be said for acclimatization. We live in the southern United States, after all, and 99° is a typical summer temperature for us (and the price we pay for having such an early growing season). Dan and I spend a lot of time outdoors, so a 15 degree difference is most welcoming when we go inside. The other benefit is that going outside again isn't a wilting shock to one's system like it is with air conditioning ("hey, it doesn't feel so bad out here"). I'll also add that in the past I've found that to run the air conditioner when the temperatures are that high means it runs nonstop, and that the electric bill is then just as oppressive as the heat.

Of course we do all the common sense things to keep the house as cool as possible:
  • vent hot air from the house at night with window fans (a whole house fan would do the best job and is on our someday list)
  • close up in the morning when outside temperature matches inside temperature
  • keep curtains drawn on sunny side of house
  • use ceiling fans
  • use a summer kitchen to keep cooking and canning heat and humidity out of the house (also the solar oven and grill)

I have to add that replacing the old windows with energy efficient ones and adding more wall insulation has helped. And I'm looking forward to being able to shade those west-facing windows someday.

The other thing we do is simply accept that summer is hot and winter is cold. That's just the way things are.

35 comments:

  1. Nice solution! We had a whole house fan in the home prior to now. They work beautifully combined with some of the extra steps you mention. But in our real log home we don't have any attic space save a tiny one over the laundry room and the main ceiling is peaked in the living room. So it wouldn't work here. But we do just about all of the tips you listed and have for years. The only one that we don't do is a summer kitchen. Maybe one :-)

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    1. Isn't it amazing how such simple steps can make a big difference?. I have to say I love my canning kitchen. I really need to make room for the coffee maker and toaster oven out there to help even more! The other things that keep the kitchen warmer than the rest of the house are doing dishes and the fridge. Last summer I was amazed to realize how much heat our fridge and chest freezer put out.

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  2. Maybe one day. Thought is but forgot to type it lol.

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    1. I wish blogger had an edit feature for our comments! I'd use it a lot. :)

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    2. Apparently I can't spell either :-) But I am with you on edit feature and the amount of heat the things that keep items cool to rock frozen put out doing so!

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    3. When we first made our pantry I thought it was a good idea to put the deep freezer and small extra refrigerator in there. Now I think it was a mistake because of all the heat they generate, especially in summer. But I don't know what else to do with them, so they stay put.

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    4. I should add that from time to time I toy with the idea of doing without them, but for now, keeping things cool and frozen is a huge help! When Dan and I talk about going off grid, these are two appliances I would find energy for. (That and my computer ;)

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  3. I keep looking for a solar powered fan for the poly tunnels that fan you have is the sort of thing I have in mind

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    1. Dawn, that's a great idea for a poly tunnel! I'll have to install one in our greenhouse whenever we finally get to it! Dan wants one for the crawlspace now. Not for heat but for air circulation to help with humidity. It gets all mildewy under there and we'd like to combat that.

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  4. I'm a big 'fan' of any passive heating/ cooling/ irrigation/ lighting etc. system. I'm glad you are enjoying a nice 15 degree cooldown in the house since you put in the fam. You guys are so on top of things. :-D

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    1. It does warm up in the house in the late afternoon, but I think that will be helped by getting something growing to shade the west windows. And of course as the night temps get higher, we can't cool the house off as much. But I'm not complaining at our progress!

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  5. LOL, yes, winter is cold and summer is hot. :-) I can only say an attic fan is wondrous thing. We have no AC but the master bedroom. Our hottest time of day on average is around 5-6 pm so opening those windows around 9 before bed and putting that fan on for the night will bring the temp inside down substantially. Clever solar attic vent fan though. When we built, the west facing windows are the smallest and protected from the direct sun by the roof overhang, deep and low on that side of the house.

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    1. Not many people build with things like that in mind, so good for you for doing so! Any kind of shading effect makes a nice difference.

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  6. The Amish adapt and here they use 12 fans. So many people are surprised we have not replaced the HVAC system as the ductwork is all still here, but we are managing the heat and it makes a huge difference in our ability to work outside. It really does feel "cool" at 84 inside and the use of window fans let's us sleep at night....with a light comforter! Your fan is now on our list!

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    1. You're farther north than me so I imagine nighttime temperature are lovely where you are!

      My worst days are the days I have to go to the library and the store. The AC in those places is too easy to get used to so that air temperatures that felt pretty good before I went into the store are oppressive when I come out. That's a big reason why we like our AC-less way of living.

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    2. Yes trips to the "modern" world of COLD full blast AC make it very difficult to stand the heat.
      Night time temps her are running 67 to 75 now.
      and I forgot to ad volt to the 12 volt fan remark about the Amish...duh my typing is dreadful
      stay cool and be well

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    3. LOL, I figured that out! We've been talking lately about doing some small solar projects with a 12-volt battery and solar recharger. Fans would be a good use for that.

      One odd thing I see in the modern world is folks who keep their AC so cold in summer that they have to wear sweaters and long pants in the house, then keep the heat so hot in winter that they wear shorts and tank tops. Makes no sense to me!

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  7. Such a sane and sensible way to go, Leigh! There certainly are ways to go without hopping onto the total "we can't survive without AC" bandwagon, aren't there? And healthier, to my mind. What a shock to the human body to plunge from summer time outdoors to a frigidly air conditioned home. And vice versa, of course.

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    1. What I have found interesting, Mama Pea, is the number of folks who are very pro-preparedness who state they can't live without air conditioning. Seems preparedness would mean learning to live without!

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  8. We keep our ac set at 80. I know that other folks find that terribly hot (we've been told!) but it is what is comfortable for us. The upstairs gets quite a bit hotter than that though, so in the evenings I open up the windows. We have had only one summer where it never cooled down at night...that was also the summer we had milk delivery service and they ruined half our milk! Last night we had the ac on because hubby had been out of town for two weeks and he wasn't used to the heat...by bedtime he was cold and I could put it back to normal. He can remember this day when the bill comes.

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    1. Which goes to show that we can get used to it! And you're right, the electric bill is often a pretty big persuader. :)

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  9. My sweetie's been pushing me to get one of those attic fans - I love the idea of a solar one, that goes on automatically. Can you share a link to the one you got?

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    1. The brand is Rand (their website here). It's not the most expensive brand, but we chose it based on customer reviews. Folks were still happy with it after 2 years of use (which says something). Amazon sells it but we got better shipping from eBay. Ours is the smallest size (20 watt) based on square footage of our attic. They also sell 30- and 40-watt fans for larger attics. I believe you'll find links there at eBay.

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  10. Great idea. It's a shame more things like this aren't designed into houses when they're first built!

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    1. Hopefully in the future that will be the case! Of course, our house was built in the 1920s, so I doubt "solar" meant quite the same thing back then. :)

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  11. No AC here either, radiant hot water baseboard heat. I ***love**** my whole house attic fan!! SW Michigan heat is not southern heat, tho the humidity can be a killer, but it knocks me down...and good points about acclimation.

    When I bought this house 17 years ago half the soffit vents were blocked off with fiberglass batting (rolleyes), 24" roof overhangs with 60% perforated soffit tho. I removed blockages, installed rafter vents and doubled the existing blown in paper insulation. It really helped insulate the house from the attic heat gain. Then when I reshingled 5 years ago I added a ridge vent, which also made a small difference in summer and helped with ice damming in winter.

    Whole house fan will rattle your brain, it's old and could probably be replaced, but it's such a great tool to direct airflow with window opening/closing once it cools down in the evening....and it exhausts the attic heat at the same time.

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    1. Sounds like you made wonderful improvements! The right improvements, because some "improvements" do more damage than good as you point out!

      Humidity is tough to acclimate to, but another reason for having those fans. Air circulation is important to prevent dampness. Dan wants to install another solar fan to vent our crawlspace. It's terribly humid under there and the vents don't seem to help very much.

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    2. Humidity/dampness make a huge difference in comfort at almost any temp. 80F at 35% is pleasant, at 90% it can be unbearable. I think that is AC's main function, to 'dry' the air and it uses the 'cold' coils to condense and remove the moisture from the air in a closed space...'closed space' being the operative variable. Impossible to mechanically remove the moisture from an open environment.

      The relative coolness of your crawl space might be part of the reason it's damp under there, condensing moisture from the ground, especially if there is no vapor barrier on the ground.

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    3. When we were looking at HVAC systems several years ago, folks told us we should look into a whole house dehumidifier without the AC. I'd never heard of that before and doubt they even sell such a thing here in the south; the AC dehumidifies as well. My only experience with dehumidifiers is that they produce a lot of heat.

      The builders of our home did not put down a vapor barrier, although Dan has laid plastic down in a large portion of it. You may be right about the dampness in our crawlspace, although humidity is often a huge problem. I'm constantly cleaning away mildew in the house.

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    4. I'm guessing that a whole house dehumdifier is attached to a forced air HVAC system....any heat generated from dehumidification would be exhausted same place the combustion gasses from heating are exhausted. I have a buddy who runs a room dehumidifier in her damp basement, I'll have to ask her if it generates any noticeable heat, but she also runs whole house AC..so may be moot.

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  12. You should try to shade the sunny windows with carpets. That's what they do in truly hot climates.
    Cheers,
    Lucía

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    1. That's a good idea! I've thought about exterior shutters as well, for both blasting sun and blasting winter winds.

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  13. My husband has been researching solar fans. I hate using our AC. We have begun replacing the windows. I patiently wait for my trees to grow, so that they will eventually shade my house.

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    1. There is something about AC that never makes the house truly comfortable. When it runs, I'm cold. As soon as it's off, I'm hot. And that's no matter what the thermometer says!

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  14. When we replaced the roof we had them install a ridge vent and then we got a whole house fan. For us it limits the time of year we need AC to only July/August. Next on our list is geothermal ac/heat system while the government is giving 30% tax credit. My daughter has one that also heats the hot water and she brags a little too much about her low electric bill.

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