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Whole House Fans
While often popular as an energy efficient solution the whole house fan is rarely recommended by RED E3. We are not fans of the whole house fan.
So most whole house fans are situated in the ceiling of home. The idea is to cool air draw air from outside and vent it through the attic where the air escapes out the gable and sofit vents. This circulates fresh cool air through the house and forces the hot air out of the attic reducing the stagnate heat load in the attic. The fan motor is efficient and sips electricity giving a powerful energy efficient cooling solution.
Sounds great! Where do I sign?But wait before you go out and buy one you should consider a few things.CFM in = CFM out
When we turn on this powerful fan it is always recommend a window or door is open. This is not a recommendation it is essential for its operation. This powerful fan is turn over a whopping 2500 to 6800 cfm's. Per the Home Energy Magazine article referenced for this page lets go with a 4,800 cfm fan. We need a minimum of 6.4 square feet of free air for the unit to run proper. If there is a screen we need to multiply the number by three to accommodate the resistance or 19.2 feet of screened opening.
We also need to vent this properly in the attic. Most attics will not have enough free air space to adequately exhaust the air. There should be about 1 square foot for every 750 cfm of fan flow. Most attics have one square foot per 300 sq ft. In a 1500 square foot house that would leaves about 1 square foot short.
Depressurization of the home.
Running a whole house fan without proper ventilation could cause the house to be in severe depressurization mode causing a whole host of problems. (see Depressurization page) Back drafting appliances and pulling CO into space being the most dangerous.
Over Pressurization of the attic.
Without proper venting the high pressure charged attic can force infiltration into the home compromising the air quality and forcing hot air into the walls into conditioned space.
Poor insulation and sealing capabilities during non operation periods.
When the fan is not running most fans I have seen are not sealed well. They have a louvered system that opens when the fan turns on and falls when the fan is off. This is not a proper seal and will allow unconditioned air into space. Furthermore the lack of insulation can add to the heating and cooling loads
So are all whole house fans bad?
No with proper design and operation whole house fans are a fantastic energy saver. When these units are properly installed and the homeowner undderstands how to operate the unit it can provide an excellent strategy to improve comfort and reduce energy usage.
Then why all the negative comments above?
I feel most fans that I have seen are not designed properly to the house. The homeowner has not been educated about its potential dangers in most cases. The most popular unit can be a net negative for energy savings.