Introduction: Whole House Fan

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

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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