Whole House Fan




About: "Better to have it and not need it than to need it and not have it."

Intro: Whole House Fan

In the middle of summer, the second floor of our home gets unbearably hot and humid. Due to the shape of our home's roof (Mansard) it cannot be adequately insulated. I've already installed an Air Conditioning unit that is over sized for the square footage of our home to no avail.

I started looking into Whole House Fans (hereafter WHFs) and as another option, but upon further research found that they needed to vented into an attic space, or outside the home. Because of our Mansard roof, and the floor plan of the second floor neither of these options was possible. We did, however, have a narrow door into the attic of the garage at the end of the hall. This was enough to set my plan in motion.

I did some research on WHFs and found information online regarding sizing the fan to the square footage of your house, pricing, *CFM (Cubic Feet per Minute), etc. I found that I needed "X" amount of CFM for my home and did some online shopping for WHFs.

STICKER SHOCK....WHFs are expensive. While digging around online I stumbled across Drum Fans. These fans are typically used for moving air around workshops, so they're pretty capable of producing gale force winds. I also found that, on average, the drum fans have a higher CFM rating than any WHF with the same blade diameter, and they were 1/3 to 1/4 the price. So I started shopping around for a suitable Drum Fan that I could convert into a WHF. I spec'd one online that moved 2,000 CFM more than a suitably sized WHF, but being "Mr Instant Gratification" I looked for one locally and luckily stumbled across local hardware store that was out of stock, but had a floor model that they'd be willing to sell for less - so I was now at 1/5 the price of a WHF.... BONUS!!!

Step 1: Parts and Equipment

Things I bought:
  • Drum Fan ($110.00)
  • 2 Plastic Outlet Boxes($0.89 x 2)
  • 1 Light Switch and wall plate ($2.00)
  • 1 Outlet and wall plate ($2.00)
  • 15' 14/3 Flexible power cord (this feels like a really thick extension cord - $8.00)

Things I already had on hand:
  • Lumber (I used what I had on hand, but 2" x 4"s or 2" x 6"s and possibly even 1" x 4"s would have worked)
  • 1/2" plywood (had some scraps handy)
  • 3 Door Hinges (liberated from an old door)
  • 2 - 3" x 3" angle brackets (had some laying around)
  • Wood Screws (I always have these handy)

  • Drill
  • Spade Bit
  • Screwdriver Bit
  • Scroll Saw or Rotozip/Dremel (for cutting the circle)
  • Chop Saw, Circular Saw, or Hand Saw
  • Screwdriver
  • Pocket hole jig, screws and accouterments (not necessary, but I used it because I had it)

Total cost came to around $125.00, but that's because I'm a pack rat, and keep things from other completed projects....sometimes even wood scraps.

Step 2: Building the Door Frame

As you can see in one of the images, the Drum Fan body is much wider than the doorway to the garage attic space. I had to build a wider false door jamb inside the garage attic  to accommodate a false door with the Drum Fan bolted to it.

I took measurements of the attic door frame while in the attic and proceeded to pieces of wood all the way around the existing attic door jamb so I would have something to attach the new, wider door jamb to. There's no need for me to share the dimensions, etc. because every application will be different.

The fan's door frame was a simple box whose interior dimensions were slightly wider than the Drum Fan's exterior dimensions. It was divided horizontally by another piece of wood that served two purposes.
  1. It served as a shelf to support  the Drum Fan's weight.
  2. I didn't have any scrap plywood long enough to cover the length of the door.
After the Frame was built I attached 1" x 1" lengths of wood to the inside of the frame. This served as a mounting point for the 1/2" plywood.

Step 3: Still Building the Door Frame

After Adding the 1" x 1" "nailers" I measured the inside dimensions of both portions of the door frame. I cut 1/2" plywood to fit and attached them to the nailers with wood screws.

The radius of the fan was determined and using that measurement I I drilled two holes in a flat piece of scrap wood I drilled two holes in a flat piece of scrap wood and used it as a makeshift compass.

I snapped a diagonal chalk line from the inside corners of the top panel and used the "X" in the middle of the board to cut a circle into the panel large enough to accommodate the drum fan. 

A door jamb was then built using 3 pieces of wood. One for the top, and two for the sides. the top matched the door frame's width, but the sides were just a bit longer(taller) than the door to allow the door to swing unobstructed by carpet of flooring once mounted.

Once the door frame was mated to the jamb I affixed the frame to the jamb temporary with scrap wood to keep the whole contraption square while I continued to work on it. I then attached the hinges to one side.

Step 4: Mounting the Fan to the Door

Moment of truth. If you did everything correctly the fan will fit in the hole.

This particular fan has a rolled lip on both the front and the back of the fan. This serves to stiffen the drum. Because of this feature, once the rolled lip is past the circular opening in the door the distance between the drum exterior and the door's circle cutout gets much wider. I used 3/4" foam pipe insulation to fill the gap. I slid the wood in the vertical slit in the pipe insulation. I found that the insulation also reduced some of the rattle.   

The bottom of the fan was bolted to the support piece in the center of the door, while the top portion was attached to the door using the 3" x 3" angle brackets. The brackets had pre-drilled holes. These holes happened to match the bolt pattern of the fan's switch housing. I simply unbolted the housing bolts one side at a time and bolted the brackets right over the housing. The pictures will explain a little better.

Step 5: Electrical

I mounted the electrical boxes on the top corner of the door, on the hinge side, but on opposing sides of the door. I drilled a hole through both electrical boxes and the panel.

I routed electrical wire from the back of the door (the attic side) towards the front. I wired a light switch at the front of the door, and an outlet at the back. I stapled the electrical wire in such a way that opening and closing the door wouldn't pinch or chafe it.

Step 6: Finale

Once I got the door jamb/door frame unit in the attic I screwed the door jamb to the attic wall and removed the wood strips that kept the whole contraption square, shut and manageable. I then wired the switch and outlet and plugged the fan it.

This thing can move a serious amount of air, but it sounds like there is a WWII era fighter plane in the attic. The attic gets pretty warm too because of its lack of insulation (that's another project) and this fan's unintended consequence is that the air that is blown into the attic from the house, although unbearably warm, is quite a bit cooler than the air in the attic. The attics air is forced out through the gable vents, ridge vents and soffits. After 5 minutes or so of running the fan the 2nd floor gets about 10 degrees cooler. We have to open the all windows on the second floor and suck the cooler outside air into the house. If all the windows in the house are shut the fan will suck air in from wherever it can, but isn't as efficient. Opening the basement windows allows cooler air from the basement to be sucked into the second floor.

You can reduce your electric bill by keeping your air conditioner off and windows shut while you are away at work. There is no need to condition the air of an empty house.

The upper floors  will get warmer, since heat rises and that is where the whole house fan comes in to play. Wait until it after sundown when the air outside gets cooler, open the upper floor's windows, turn the WHF on and let it displace the warm air inside with the cooler air from outside. leave the fan on until all the warm air has been evacuated, shut off the fan and turn on the Air Conditioner. Whole house fans are not meant to be on all day, or night, long.



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    19 Discussions


    Reply 2 years ago



    3 years ago

    Great Instructable! What exhaust fan did you go with, what size, and for what price?
    Centric Air units are nice, but pricy. Looking to recreate a DIY version w fan, large insulated flex ducting, and louvered grill. Not finding affordable sources yet.
    Thanks again for sharing, CementTruck!

    2 replies

    Reply 3 years ago

    I didn't make any changes with exhaust fans yet. I'm thinking of adding a large window in the attic so the drum fan can exhaust the air through a larger opening.


    Reply 4 years ago on Introduction

    Thanks for the input @shortw. I thought as much, but as I mentioned "I am no expert" and will be the first to admit it. I'm glad you chimed in.

    Do you have any background in this area, or are we cut from the same DIY cloth?


    5 years ago on Introduction

    I grew up in California. My dad installed a powerful roof fan on our house for the hot summer months. Now I still love sleeping with white noise no matter what the temperature is!


    6 years ago on Step 1

    I'm not sure what your local climate is like JTomM129. Evaporative coolers work really well in hot dry climates, like Arizona, and New Mexico, but don't do much good in humid regions. They can also start the growth of dangerous molds in carpet and gypsum boards. If you live in a dry climate then this sounds like a great solution for your particular issue. Kudos on the carbon footprint reduction.


    6 years ago on Step 1

    Hiya CementTruck!

    I just did a sweep of Amazon and found several drum fans slightly smaller (14 to 18 inch diameters) with 3 speeds for under $75 USD. Maybe slightly less fan at a lower speed will sound less like the Spitfires revving up to meet the Luftwaffe over the Chanel but still be enough to cool the place down . . . Just a thought. Also, I was thinking of building a "inside the room vented to the window" (anti covenant restrictions) evaporation cooler at one end of the home with smaller fan(s) blowing inward and a larger "exit fan" (like you WHF) at the other to channel the cooler air throughout my condo. I have a "Shotgun style" Condo (windows and sliding doors at either end of the long floor-plan with the over all effect of a long box with opening on each end) and figured if I could cut 10 to 15 degrees F off the outside temp. by channeling cool air though the tube I could leave my 25 year old inefficient AC unit off and still be more cost efficient and green(er). It turns out a few floor fans work well enough for me for this summer so I've let that idea slide for now, but may try it next year to reduce my carbon foot print.


    Reply 6 years ago on Step 6

    I agree, great idea,

    I will be doing something very similar. and I have a 1 & 1/2 Story addittion to our house that is a self contained home. The roof is tin, and I guess is not too well insulated, I was planning to put a cavity using drywall over some insluation and using small computer fans (12v) and some PV solar panels to run the fans whenever there is light, any thoughts?


    Reply 6 years ago on Step 6


    Thanks for the shout out.

    I don't know how many computer fans you'll be using, however, PC fans don't move that much air, and so you'd need a lot of them. There are solar roof vent fans that move a little more air (CFM) . The drum fan I installed, however massive, makes the indoor temperature more tolerable, but not as much as I had hoped, or expected.

    Depending on where you live, how much sun you get throughout the day, your budget, and a few other factors, the first thing I would suggest is insulating under the tin roof. This will probably be the best bang for your buck at cooler indoor temps. You would need a gap between the underside of the roof and insulation for airflow, as well as a way for that airflow to be refreshed continuously.


    Reply 6 years ago on Step 6

    Cement truck,

    Hey BIG thx, I had thought abot air flow CFM, but now you have made me think more I was thinking to have quiet a few, but as you said, need to understand the CFM better. The roof is insulated some, I do not want to take all what I have of a ceiling down to find out, I was just going to re insulate with batten cavitity with insulation. But the solar roof vent fan sounds good, your points about air flow with insulation is a good remindered for us all as it is often forgotten. PS based in mid OHIO, not the hottest of places, but hot enough for action! :-)

    as for the drum fan, I am definitely, due to you , going to do that. just really like the idea of learing out large volumes of heat quickly, then suplement with specific a/c when you want to, than as you said, putting some ac on all day.

    thx again.
    Rgds Colin


    7 years ago on Introduction

    This turned out very well. An even cheaper alternative is to use an attic exhaust fan (Amazon has them for about $50). Probably would not move as much air as your setup but for those without quite so dire needs, it should work!

    1 reply

    Reply 7 years ago on Introduction

    Thanks kidproquo.

    I already had an attic fan. You're right, it didn't move enough volume, so I had to improvise with this monster.


    7 years ago on Introduction

    When I was kid we didn't have A/C , we use an atic fan, this while living in Florida.

    Man that thing sure made the curtains stand straight out. Seems like that was the best sleep I ever got.

    Good instructable and idea!

    1 reply

    Reply 7 years ago on Introduction

    Florida without A/C? Whew!

    I used to live in Eglin AFB/Ft. Walton Beach a couple of lifetimes ago, and as far north as that was it was still pretty warm. I miss it though. I also lived in a tropical country for 16 years without A/C and it didn't seem to bother me then. Ocean breezes make a BIG difference. Thjs mid-west heat and humidity sans breezes are a whole 'nother issue though.

    Thanks for commenting.


    7 years ago on Introduction

    Are you worried about backdrafting? If you are forcing air out of the house through a fan, it could cause carbon monoxide from your furnace to be sucked backed indoors. Other than that, this is a great 'ible.

    1 reply

    Reply 7 years ago on Introduction

    That's a good question. I'm no expert so I couldn't tell you for sure, but my furnace has an electric version of a "pilot light", so there isn't a flame burning all year long, and since this fan is only used in the summer the furnace isn't used at the same time, so I'm assuming I'm safe. I should probably be worried about Radon being sucked throughout the house though.

    Another thought too would be the fact that whole house fans even exist, and are sold daily.

    I'll have to do some research and get back to you on this. This was just my gut instinct.

    Thanks for commenting.