Whole house Fans

(Terrill Ewald, CPI, MD# 31310) #1

Are there ventilation requirements for installing a whole house fan? 1200 sqft middle townhouse with ridge and soffit vents only. Seems like if fan was used it would apply positive pressure to attic space.

(Christopher Foley) #2

Yes there is a 'science' to it. I dont like when there is not a mechanical gable louver vent designed for such whole house fan. A ridge vent is not designed for the fan although it may work in conjunction with fixed roof vents. But that needs to be figured out by one who installs the fan - not us nor the handyman/homeowner who probably installed it. I state in my report ' whole house fan was turned on by the switch located at XX and the fan operated as did the hallway ceiling louvers open and close properly. The fan is designed to work by taking warm air out of the house expelling it out through the attic non mechanical vent system and replacing interior air with cooler exterior air via OPEN windows. This inspection does not calculate nor imply that the current attic venting is properly designed to allow for proper venting of the whole house fan.
Recommend further review of attic venting by licensed house fan professional to ensure current conditions meet proper venting.'

(Terrill Ewald, CPI, MD# 31310) #3

Great, Thank you

(Christopher Foley) #4

This is from energy.gov site. Sums it up Doubt your attic has extra venting design per sq foot as described below
Attic ventilation will usually need to be increased to exhaust the fan's air outdoors. You'll need 2 to 4 times the normal area of attic vents, or about one square foot of net free area for every 750 cubic feet per minute of fan capacity. The net free area of a vent takes into account the resistance offered by its louvers and insect screens. More vent area is better for optimal whole house fan performance.

If your fan doesn't come with a tight-sealing winter cover, you should either buy one or build one. If you switch between air conditioning and cooling with a whole house fan as the summer weather changes, build a tightly sealed, hinged door for the fan opening that is easy to open and close when switching cooling methods.

Be cautious when operating these large exhaust fans. Open windows throughout the house to prevent a powerful and concentrated suction in one location. If enough ventilation isn't provided, the fans can cause a backdraft in your furnace, water heater or gas-fired dryer, pulling combustion products such as carbon monoxide into your living space.

(Greg Keene, CMI) #5

Lack of sufficient clear opening space will probably cause "cavitation" and the noise sounds like a helicopter in the attic.

(Thomas Witt, CMI MD. Lic. # 30933) #6

[quote="tewald, post:1, topic:101498"]

Are there ventilation requirements for installing a whole house fan? 1200 sqft middle townhouse with ridge and soffit vents only. Seems like if fan was used it would apply positive pressure to attic space.
[/QUOTE]

Unusual to see a whole house fan installed on a small townhouse like that.
Typically the only time I see the are on larger, older homes.

(Erik Schmidt) #7

Where is that fan moving air from, from inside the house into the attic?

(Terrill Ewald, CPI, MD# 31310) #8

Yes, installed over stairwell.

(Thomas Witt, CMI MD. Lic. # 30933) #9

[quote="eschmidt, post:7, topic:101498"]

Where is that fan moving air from, from inside the house into the attic?
[/QUOTE]

The idea behind a whole house fan is a good one, you have a warm day with a cool night and you just open some windows and turn on the fan.
Exhausts the hot air and brings in the cool night air.

But, it has to sized and vented properly.

(Erik Schmidt) #10

That might work in the tropics, ie not not worth a dam in Alberta, and it might work better elsewhere too if it was attached to an insulated duct to the exterior. The one in the pic is looks like about a 2 X 2 void in a well insulated attic, nothing to stop conditioned air from entering the ventilated attic, so big time condensation problems when it is cold out.

(Kenton Shepard, CMI) #11

Coupled with a window-mounted swamp cooler in dry climates zones they work really well.

(Eliezer Santiago) #12

Are house fans parts of the SOP? If the anwers is yes, where can I find it?

(Wayne B. Wilson, TN 439) #13

In the mold capital of the USA not such a great idea . open windows and sucking crap in .

(Stephen H. Payson) #14

You can start by actually reading the SOP