Wednesday, September 5, 2007

Whole House Fans

Whole House Fans are:
  • inexpensive to buy ($150-250)
  • energy saving (we saved $158.63 during the first spring of operation. Payback less than one year)
  • easy to install
  • cool well
  • allow you to direct cooling breezes throughout the house
  • significantly reduce energy bills
  • add to feeling of being a part of nature
  • Utility Company Rebates (google "whole house fan" rebate )

September marks the end of the hot, muggy and windless Chesapeake summers and the beginning of our wonderful and quite long fall season here in the mid-Atlantic, a perfect time to turn off that energy hogging AC and open those windows for night time cooling.

Our single story ranch, however, is difficult to cool using the natural passive "cooling chimney" techniques available to two-story home owners. That's why I installed a Whole House Fan last winter to reduce our home cooling bills during the long spring and fall months (see Energy Usage chart at left to compare March-July 2006 to 2007 after the fan was installed).

Normally installed in the ceiling of a hallway, these fans and automatic louvers come in two models: direct drive and belt drive, and in two sizes: 24x24 inch and 30x30 inch. Cost starts under $200 at the home improvement stores. Installation only takes an hour or two, depending on your abilities, but is well within the do-it-yourselfer's skills.

While some models require the homeowner to cut a ceiling joist to box in the fan, at least one brand (Air Vent) has bracket hardware to allow the fan to sit atop the joist. The installer then fits stiff cardboard (included) between the fan box and the ceiling below to seal the air flow. (note: click image to enlarge and inspect the bracket placement on top of joist and staples holding the cardboard in place to seal airflow. Not shown: I scored the cardboard on one side and folded it into an "L" shape, and then stapled the short leg of the "L" to the ceiling and the long side to the fan box.)

All that remains is to wire the motor for regular household current (120 volts), cut the sheet rock inlet hole, and install the automatic louvers. This particular fan is controlled by a pull chain and has two speeds, but wall mount controllers are available.

To begin enjoying the joys of your cooler seasons, turn on the whole house fan, open windows in living areas or bedrooms to control air flow.
If we only open windows on the shaded side of our home, we are usually comfortable inside the house using the whole house fan alone in temperatures up to 85 degrees.

  • before you cut into your ceiling, be sure you have enough attic room above the fan (the attic space above my hallways was blocked where roof supports joined the ceiling joists)
  • direct drive fans are reported to be somewhat more noisy than belt drive fans. However, direct drive fans are not prone to the belt noise of some belt driven fans.
  • if you are not comfortable with 120 volt connections, hire an electrician for this part
  • a 30x30 inch whole house fan operating on high requires about 7 sq. feet of exhaust vent from your attic. You may have to add a bit of exterior venting in the form of passive gable or rooftop vents. Don't forget to calculate in the area of soffit vents under the eaves and ridgeline vents on the roof, if you have them. (Note: for exit vent calculations, screening over vents reduces air flow by about half the area). Ignore this warning and you may blow down a weak section of ceiling when you over-pressurize the attic--I did, fortunately it was in the garage and easy to repair.

A bit odd, but it works:

I mentioned that whole house fans are usually installed in hallways, but we couldn't find a place inside the house where it was easy to get to from above and below. So we installed our whole house fan in the attached garage. Of course, the connecting door has to be open between the house and the garage for the fan to work.

Advantages of installing in the garage:
  • less noisy
  • usually no itchy blown-in insulation over the garage to fool with
  • with AC on and the house buttoned up, the whole house fan vents and cools the garage while I'm working on a project
  • removes paint and varnish fumes from garage
  • removes heat from parked cars and vents it out the attic
  • with AC on in the house and the garage bay door open, the whole house fan will force super heated air out of the attic and replace it with cooler air from the garage, reducing the load on my AC system (my ducting is in the attic).
Disadvantages of installing in the garage:
  • door open between garage and house. We use a pet gate to keep the dogs in the house and out of dangerous substances in the garage.
  • mice can crawl into the house through the pet gate (this has not happened yet, and in any event, our three cairn terriers would count a mouse in the house as a bonus, not a disadvantage. The seem to recognize this and sleep in shifts watching the gate at night, hopeful for a critter incursion)
We love laying in bed together on a cool fall night, snuggled together under our comforter. We listen to the splashy fountain outside our window and the nocturnal sounds of nature being drawn into our bedroom on the breeze from our whole house fan.

1 comment:

High Voltage Electrical Tech said...

This is is a great article on whole house fans. I found a link to a whole house fan calculator that made it easy for me to buy the correct size fan for my home.

Its at