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Thread: Whole house fan

  1. #1
    DIY Member mar3232's Avatar
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    Default Whole house fan

    Don't know why I've overlooked these in my quest for cutting costs on AC and from my research, nearly everyone is pleased with them. I'm in Indiana where we can have some pretty cool summer nights as well.

    Question though --

    I have a small ranch house, just 1600 sq feet and was wondering rather than just one centrally located fan, is it OK to install 2 or more? My bedroom is a big concern, so I really would like a smaller one in there and then a larger one 25 feet away in the living room. I could keep the bedroom door closed -- don't know if there is some sort of weird interaction between 2 fans or not ?

    Sounds like belt drive is the way to go -- anyone that has experience with particular make/models would be appreciated.

    Thanks much.

  2. #2
    DIY Member mar3232's Avatar
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    Also, I wonder if I were to build a nice enclosure(s), if gable fans would work? Sure would save money -- they aren't very expensive.

  3. #3
    DIY Member mar3232's Avatar
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    Like, maybe one actual gable fan for the gable itself plus 2 gable fans turned backwards in nice boxes for the house fans? < 150.00 for all 3?

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    DIY Senior Member BobL43's Avatar
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    Quote Originally Posted by mar3232 View Post
    Like, maybe one actual gable fan for the gable itself plus 2 gable fans turned backwards in nice boxes for the house fans? < 150.00 for all 3?
    I'm not sure, but I do know that you must have enough attic venting to allow all the air pushed into the attic by a ceiling mounted fan to get out without pressurizing the attic, and have enough sq inches of open windows or doors to supply air to the fan without creating a negative pressure in the house. I have a big attic fan in my house in my den ceiling, which is at one end of the house, and it works great, (but see below, lol) except for the noise. It is an old direct drive on, with the big fan blade mounted on the motor shaft.

    The real problem with this, is that in the real heat of the Summer, it pulls in WAY too much humidity (Long Island, NY) even on cool evenings.
    When all that humidity is back in the house, It takes a LONG time for the central AC to pull it back out again. I assume you mean that you will turn on the AC again in the morning?

    I don't even use that fan anymore except when my wife cooks something that produces enough smoke to set off the smoke alarms; that fan will clear the house out quickly. In the Spring, it might be OK, but it would pull in all that pollen and get everything coated with green powder just like everything gets outside.

    Maybe you did not mean a whole house fan, and meant an attic fan? No, I see you meant whole house fans, in my re-reading. Using more than one, may cause some problems without sufficient venting to let the air out of the attic, like forcing hot attic air down one of the other fans, possibly.

    My Attic gets so hot in the Summer, and it gets the house so hot even with R30 insulation, which nowadays seems to be minimal.

    I need to keep my Attic cooler.
    I am definitely not a pro plumber, but I am a pro crastinator

  5. #5
    DIY Member mar3232's Avatar
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    Maybe that's what I should try first -- cooling the attic better. I don't want to bring humidity INTO the house but I'll take your word for it, thought that a whole house fan would help dry out the air.

    Beads of sweat I don't want.

    Yeah, I thought using the whole house fan evenings till AM and then AC during the day if I need it.

    So maybe whole house fans are over-rated? Every youtube owner seems to love theirs -- even a guy in LA.

    I'm just looking to be greener (but not at the sake of comfort) and save on my AC bill as well.

  6. #6
    Jack of all trades DonL's Avatar
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    When I lived in Central Indiana we had 1 Gable Vent at one end of the house and 1 Gable fan blowing out at the farthest Gable location.

    That is all that was needed, No Air Condition system was needed.

    The only thing nice about the belt driven, was they have a bigger motor and bigger Blades that would move a bunch of air.

    Run Less but take more electricity when running.


    Air Conditioning was luxurious when I was growing up in the Indian No Place.
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  7. #7
    In the trades Dana's Avatar
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    Quote Originally Posted by mar3232 View Post
    Maybe that's what I should try first -- cooling the attic better. I don't want to bring humidity INTO the house but I'll take your word for it, thought that a whole house fan would help dry out the air.

    Beads of sweat I don't want.

    Yeah, I thought using the whole house fan evenings till AM and then AC during the day if I need it.

    So maybe whole house fans are over-rated? Every youtube owner seems to love theirs -- even a guy in LA.

    I'm just looking to be greener (but not at the sake of comfort) and save on my AC bill as well.
    Yup- they're over rated in climates with dew points as high as yours. It take literally twice as much cooling power to lower the dew point 10F than it takes to lower the sensible temperature 10F. "Healthy" 50% RH/75F air has a dew point of 55F, and the average summertime dew point in the mid-60s.

    Summertime dew points in IN average in the mid to high 60s (depending on location), so there's no point to sucking in 65F dew-point air overnight to lower the sensible cooling load by 5-10F, while raising the indoor air dew point by 10F. The guy in LA who loves his whole house fan sees mid summer average dew points of about 60F.

    Also note, whole house fans are usually pretty leaky, and represent a 24/365 infiltration leak. Better to spend your attic-upgrade money on AIR SEALING between the attic and conditioned space first, and adding more R in the form of blown cellulose (not low-density fiberglass, which is less air retardent and is translucent to radiated heat, making the insulation 1-2" in from the top several degrees hotter than the attic air when the roof deck is hot!) Up to R50 is cost-effective long term, but even when not cost effective, R50 can be "worth it" from a comfort point of view. Apply the cost of a whole house fan to "extra" cellulose and it's still a better deal. A 3-10" overblow of existing batts or low-density stuff is fine-you're looking for a total depth of old + new in the 12-15" range.

    If you have a ducted whole house AC system with ducts in the attic it's a energy pig relative to just about any ductless mini-split. With a high-R attic, and some exterior shades on E & W windows (and maybe awnings or over hangs on the S windows) you could probably cool the whole house with a better-class 1 ton mini-split with a "set and forget" approach to temperature, at ~2x the as-used efficiency of a 13 SEER ducted system. But with any ductless approach floor plans and high solar gain areas doored off from the main zone matter.

  8. #8
    DIY Member mar3232's Avatar
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    Ok -- this whole fan thing was a diversion from my real objective which is, when I get the money, a ductless mini split. Speaking of sealing the attic from the living area (and in preparation for my eventual mini split), I actually sealed all of my ducts and the return with some masonite board. (I have no intention of repairing my Trane ducted system). Is it my imagination because when I did that, I can't believe how much easier it is to heat and cool my house.

    Especially cooling -- compared to last year I noticed an immediate difference in my single (temporary) window AC unit's ability to perform.

    The ductwork is insulated very well but it does run overhead through the attic with ceiling vents.

    Can attic overhead vents like that really effect efficiency? I mean especially when the system is idle it has to be heating all that air in the ducts pretty well.

    I really noticed a difference in comfort when I sealed all mine.

    I'm looking forward to get the mini split installed -- don't have the dough right now.

  9. #9
    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by mar3232 View Post
    ...
    The ductwork is insulated very well but it does run overhead through the attic with ceiling vents.

    Can attic overhead vents like that really effect efficiency? I mean especially when the system is idle it has to be heating all that air in the ducts pretty well.
    I have that kind of problem. The ductwork in the attic is smooth (not flex) and insulated, but a technician has shown me the poor numbers he got while checking overall efficiency. If I can ever afford to do so, I would like to run ductwork below the ceiling (and then cover it with a lower ceiling) to resolve that.
    "Great minds discuss ideas, average minds discuss events and small minds discuss people." --Eleanor Roosevelt

  10. #10
    In the trades Dana's Avatar
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    Depending on the roofing color and orientation, having even insulated & sealed ducts in the attic can add a full ton of peak cooling load. If the ducts are not sealed on every seam & joint it can add more.

    Putting masonite over the registers very likely reduced the amount of stack-effect infiltration through the house by making the ceiling more air-tight, which has a dramatic effect on reducing latent-load, if somewhat lesser (but still significant) effect on the sensible load. Caulking/foaming/blocking every ceiling penetration of plumbing & electrical, flue-chases etc. is worth it, as is air-sealing the foundation sill & band joist, putting in better dryer-vent backflow prevention etc. in the basement to slow down stack-effect infiltration, which makes a difference both winter & summer.

    Some states and utilities offer rebate type incentives for installing mini-splits that meet minimum efficiency standards (eg: http://www.duke-energy.com/indiana/s...mart-saver.asp. and it's highly likely that you qualify for some of that. But it's also possible for reasonably handy people to do a DIY install (but I'd still have a qualified tech complete the full commissioning & testing to ensure efficiency), and you can get a pretty-good 1 to 1.5 ton ultra high SEER heating & cooling mini-split for under $1500 at internet prices: or http://www.amazon.com/Fujitsu-Single-Split-System-AC12RLFW/dp/B007TY27UG/ref=sr_1_1?s=hi&ie=UTF8&qid=1338473927&sr=1-1. The difference in cost between a cooling-only or heating & cooling version is usually a few hundred, and if you heat with oil, propane, or electricity it'll take a HUGE chunk out of your heating bill too. (Not so much if you're heating with gas, unless you have cheaper than average electric rates.)

    Installed by a pro it'd probably run you close to $3-3.5K for a 3/4ton or 1-ton, and a 1.5 ton would typically be in the neighborhood of $4K. A 1600' house with a reasonably high-R attic, decent windows and reasonable air tightness wouldn't usually need more than a 1.5 ton even at 110F, and the 1% design temps for IN run about 90F, so a 1-ton in the largest zone would likely carry the whole thing without much trouble. (If you've been living with a window-shaker in the bedroom and it's mostly keeping up, it'll be a noticeable improvement in comfort, noise, and operating cost.)

    If your east & (particularly) west windows are clear glass (even double-panes) it's worth buying low-E storm windows (at $150-200/window, for a typical double-hung), which will cut the solar gain when the sun is low in the sky, since overhangs can't protect it on the E & W sides the way it can on the S side. This makes for big uptick in wintertime performance too. If the windows you have are low-E gas-filled U0.34 or lower don't bother, but a low-E storm over a bottom-of-the-line U0.60 double pane beats code-min replacement window performance at a fraction of the installed cost. South facing clear glass still reflects most of the summer heat due to the high sun angle, but in winter when the sun is lower at mid-day the solar gain is useful rather than harmful. If single-pane clear storm windows on the south side are worth it though.

  11. #11
    Plumber jimbo's Avatar
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    Whole house fans are very helpful in a climate where it cools off after the sun goes down. They are quite popular in the inland areas of Southern California, where it might be 100+ during the day, but dry, and down to 68 early evening and overnight. If you have not air conditioning, the house gets quite hot, and tends to STAY hot, making for poor overnight comfort. But turn on that fan which will suck the rear end out of a frog, and you get the house nicely cooled down.

    I would be careful about using two, as they may compete with each other and adversely affect air flow.

  12. #12
    Jack of all trades DonL's Avatar
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    All you really need is a Floor fan to cool your Body.

    They are star rated and you can get them at Wallie Weird for $20 bucks.
    Last edited by DonL; 05-31-2012 at 08:55 AM. Reason: French
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    DIY Senior Member BobL43's Avatar
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    Quote Originally Posted by jimbo View Post
    Whole house fans are very helpful in a climate where it cools off after the sun goes down. They are quite popular in the inland areas of Southern California, where it might be 100+ during the day, but dry, and down to 68 early evening and overnight. If you have not air conditioning, the house gets quite hot, and tends to STAY hot, making for poor overnight comfort. But turn on that fan which will suck the rear end out of a frog, and you get the house nicely cooled down.

    I would be careful about using two, as they may compete with each other and adversely affect air flow.
    I envy your climate Jimbo. I've been in San Diego in the Summer time. I'd probalby move there if I could afford to and could lose my fear of forest fires, mud slides and Earthquakes.
    I am definitely not a pro plumber, but I am a pro crastinator

  14. #14
    DIY Senior Member BobL43's Avatar
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    Quote Originally Posted by DonL View Post
    All you really need is a Floor fan to cool your Body.

    They are star rated and you can get them at Wallie Weird for $20 bucks.
    Don, we actually have a ceiling fan in every room in the house except 2 of our 3 bathrooms. Fllor fans work well too, but its difficult to get any serious paperwork done. Kinda like Lucy and Ethel or Abbot and Costello. I'm going to put my extra ceiling fan in my Gazebo. Of course it will be a damp area rated unit, and done to code. I will not be using a ground rod for it Don; should I ? Shields UP, tail down.
    I am definitely not a pro plumber, but I am a pro crastinator

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    Jack of all trades DonL's Avatar
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    Quote Originally Posted by BobL43 View Post
    Don, we actually have a ceiling fan in every room in the house except 2 of our 3 bathrooms. Fllor fans work well too, but its difficult to get any serious paperwork done. Kinda like Lucy and Ethel or Abbot and Costello. I'm going to put my extra ceiling fan in my Gazebo. Of course it will be a damp area rated unit, and done to code. I will not be using a ground rod for it Don; should I ? Shields UP, tail down.
    No Ground Rod needed.

    But in a setting like that I am sure a Rod will pop up.
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