Whole House Fans
Whole House Fans | These simple pot vents are great exhaust ports for a whole house fan. You may need quite a few to satisfy the power of the fan.
DEAR TIM: While doing a walk through inspection in our new home our builder indicated that he could not put in the whole house fan we wanted. The reason he gave was that both roof vents and eave vents had been accidentally installed. I believe he called them continuous ridge and soffit vents. The builder said the whole house fan would burn up and offered a credit to us. Is this correct? We really want the whole house fan. Kristi B., Manteca, CA
Dear KRISTI: Ooooops! What does the builder mean "accidentally"? The location of your home in the central valley of California needs as much ventilation as possible. If I was building your home, the continuous ridge and soffit ventilation would have been just one part of the roof ventilation package. The great news for you is that you can have the whole house fan installed and it will not burn up so long as your builder and roofer team up and install some extra roof ventilation products.
Do whole house fans work well in all climates?
Whole house exhaust fans come in different types and sizes. Their sole purpose is to move vast quantities of air. They work very well in climates that have moderate to low humidity. As the sun goes down and the outside air temperature begins to drop, a whole house fan can create pleasant breezes through any and all rooms of a house. Ask anyone who has one and they will tell you that even during peak summer months, they sometimes have to sleep under a blanket!
How much exhaust area is needed for a whole house fan?
These fans pull hundreds and even thousands of cubic feet of air per minute into your home. For them to work at peak efficiency they have to push an equal amount of air out of the attic. If there are no places to exhaust air or the exhaust areas are small, the fan blade spins but it doesn't really push much air. Low air flow past the fan motor can cause it to overheat. Spinning car tires on snow and ice are a fairly accurate analogy. A car engine can rapidly overheat in this situation as the car's radiator is not moving through the outdoor air.
When you purchase a whole house fan the written instructions clearly state how much free net area of exhaust the fan needs. The net free area is often called out in square feet or square inches. But don't be fooled. If you cut a one square foot hole in your roof and cover it with some sort of cap, you do not have one square foot of exhaust opening. The insect screening or slits in the metal vent can cut off as much as 50 percent of the hole you created.
I always prefer to exceed this amount by 25 to 50 percent. One way to achieve this required ventilation area quickly is to install simple and affordable spinning roof turbines.
Will spinning roof turbines help exhaust air?
These wonderful roof ventilation products may not look as sleek as the hidden continuous ridge and soffit ventilation you already have, but they also allow massive amounts of air to readily escape from your hot attic space. What's more, they work anytime a slight breeze blows across your roof. I would install these on the back side of your roof so they are not visible from the street.
If you don't like roof turbines you can have your builder install simple static roof pot vents. These are very common roof ventilation products and they work well. I have them on my own home. But depending upon the fan you have purchased, you may discover you need 10 or even 15 of these pot vents to satisfy the whole house fan. Once again, place these vents on a part of the roof that is least visible from the ground.
Don't let your builder pull the wool over your eyes with an expensive change order for this work. The actual materials you need to provide the necessary ventilation for the fan will probably cost you less than $150.00. The time to install the products might be less than 4 hours. In my opinion, the builder should not charge you for the time since he already told you he was going to install the whole house fan in the first place. Necessary roof vents are a part of this package.
The spinning roof turbine vents are an excellent match for whole house fans. The beauty of them is that they do not restrict the amount of opening in the roof. In fact, when they spin either by wind power or air being pushed by the whole house fan, they exhaust far more air than they would if the hole in the roof was simply open to the atmosphere.
The truth be told, you can't have too much roof ventilation. Ask any farmer that raises chickens and they will show you how they ventilate the chicken houses since chickens can't sweat and need to be cool or they die.
Where Are the Fans?
In the June 20, 2021 AsktheBuilder Newsletter, Lewis emailed asking, "Why do you rarely, if ever, see whole-house fans in new houses?" CLICK HERE to read the answer.
Column 491