Whole House Fan and How to Benefit From It
Where and when it makes sense to use the whole house fan
* Preferably mild climates with cooler and less humid nights
* Use it only if the temperature and humidity outside is more favorable than the conditions indoors. If your air conditioning system has been operating during the day, and the temperature outside drops lower (but the humidity is still high), don't turn the whole house fan on. The vent will suck all the humid air into your air conditioned house
* The best time periods to use it would be, of course, early morning and evening
Who shouldn't use the whole house fan?
If you suffer from allergies, it might not be a good idea to bring all the pollution into the house. The window screens will stop some of it, but whole house fans are very powerful and will make you sneeze more than ever.
Physics of the whole house fan operation!
1. Before you turn the fan on, open as many windows and doors as possible, close fireplace damper and / or glass door, and shut the furnace / water heater room doors (if they are louver type, it won't matter). The suction of the whole house fan (at least at the highest speed) is so great, that without open windows / doors, it will draw air from the outside through any possible openings like, for example, from the chimney. If it is a fireplace chimney and you don't remove the ashes... well, it's going to be a mess. If it is a water heater / furnace chimney, it might blow off the pilots.
2. When everything is ready, you can turn on the whole house fan and usually within the next few seconds you should feel plenty of exterior air flowing around the house. Unless...
3. This part is equally important as opening the doors and windows - both have to be balanced to function properly in order to really benefit from the whole house fan operation. The air drawn by the whole house fan has to be discharged through the attic vents to the exterior. Otherwise, pressure created in the attic area will cause the air that was just pulled out of your house to return with dust and insulation particles through any possible gaps in the attic floor and the whole house fan itself.
Regular attic ventilation might not be enough to support the whole house fan operation; you might need much more to carry all that extra volume of air to the exterior. And the formula to calculate the square footage of the attic vents required to discharge that air is very simple. All you need is the dimensions of all your rooms:
Example: your ceilings are 8' high and you have four 10' x 14' rooms, one 15' x 17' room, and a 10' x 3' hallway (this is just a sample, calculate all the rooms in your house you think should be covered)
10'x14'x8' = 1120x4 = 4480
15'x17'x8' = 2040
10'x3' = 30
Total - 6550 cubic feet
Now you have to divide 6550 by 750, which equals 8.73 sq feet - this is the area of the required attic vents (all of them combined - soffit, ridge, gable, etc.)
4. If the house you're moving into has the whole house fan already installed, lets hope that it was properly sized up for its purpose (there might be a tag on the unit itself), which is to replace your house air within just a few minutes.
5. If you're the one installing the whole house fan, consider 3 or 4 minutes as an optimal time for the house air exchange. To achieve that, you'd need to divide your house total air volume (6550 cubic feet from our sample) by 3 or 4 minutes. That will give us 1810 CFM / 1357.5 CFM (Cubic Feet per Minute).
6. One more important thing: louvers of the typical whole house fan are not air tight and have no insulation applied on their surface; they leak air between the house and attic. I would highly recommend installing a whole house fan cover in attic area to prevent air drafts during the cold season - don't forget to remove it before you decide to use the fan again.
Whole house fans are noisy and many people never use them, but they might benefit your wallet if you apply all of the above. There are currently other types of house ventilation systems available: they are more expensive (2 - 3 times) but very quiet, more efficient, and provide air circulation for extended periods of time.
Have a cool summer next summer.
About the Author
Dariusz Rudnicki is a licensed Illinois home inspector who has been in this business for over ten years, crawling through the areas you would newer expect that even exist in your house ... just to let you now that everything is working properly... or not. Are you preparing your house for sale or having some problems with your property? All you need to do is ask him for a house maintenance advice - that is all it takes to get help.
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How To Reduce Your Energy Bills / Energy Conservation Begins at Home
Imagine leaving a window open all winter long -- the heat loss, cold drafts and wasted energy! If your home has a folding attic stair, a whole house fan or AC Return, a fireplace or a clothes dryer, that may be just what is occurring in your home every day.
These often overlooked sources of heat loss and air leakage can cause heat to pour out and the cold outside air to rush in -- costing you higher heating bills.
Air leaks are the largest source of heating and cooling loss in the home. Air leaks occur through the small cracks around doors, windows, pipes, etc. Most homeowners are well aware of the benefits caulk and weatherstripping provide to minimize heat loss and cold drafts.
But what can you do about the four largest “holes” in your home -- the folding attic stair, the whole house fan or AC return, the fireplace, and the clothes dryer? Here are some tips and techniques that can easily, quickly and inexpensively seal and insulate these holes.
Attic Stairs
An easy, low-cost solution to this problem is to add an attic stair cover. An attic stair cover provides an air seal, reducing the air leaks. Add the desired amount of insulation over the cover to restore the insulation removed from the ceiling.
Whole House Fans and AC Returns
An easy, low-cost solution to this problem is to add a whole house fan cover. Installed from the attic side, the whole house fan cover is invisible. Cover the fan to reduce heating and air-conditioning loss, remove it when use of the fan is desired.
Fireplaces
A recent study showed that for many consumers, their heating bills may be more than $500 higher per winter due to the air leakage and wasted energy caused by fireplaces.
An easy, low-cost solution to this problem is to add a fireplace draftstopper. Available from Battic Door, a company known for their energy conservation products, a fireplace draftstopper is an inflatable pillow that seals the damper, eliminating any air leaks. The pillow is removed whenever the fireplace is used, then reinserted after.
Clothes Dryer Exhaust Ducts
An easy, low-cost solution to this problem is to add a dryer vent seal. This will reduce unwanted air infiltration, and keep out pests, bees and rodents as well. The vent will remain closed unless the dryer is in use. When the dryer is in use, a floating shuttle rises to allow warm air, lint and moisture to escape.
If your home has a folding attic stair, a whole house fan, an AC return, a fireplace, and/or a clothes dryer, you can easily, quickly and inexpensively seal and insulate these holes.
Mark D. Tyrol is a Professional Engineer specializing in cause and origin of construction defects. He developed several residential energy conservation products including an attic stair cover, an attic access door, and is the U.S. distributor of the fireplace draftstopper. To learn more visit www.batticdoor.com
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That's great, I never thought about Whole House Fan and How to Benefit From It like that before.
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