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Whole house fan blows away our A/C bill.

Picture of Whole house fan blows away our A/C bill.
In certain climates a whole house fan (WHF) is an effective way to offset the high cost of air conditioning.   The theory works particularly well in areas with very hot days and nice cool nights like the Central Valley of California where we happen to live. The WHF is installed in the ceiling and blows upward into the attic to force the hot air accumulated during the day out your  roof vents while sucking cool nigh-time air into the house through open doors and windows.   In the morning, the fan is turned off and windows and doors are closed up to prevent the cooled interior from warming up.

For many homes, installation of a pre-manufactured WHF is quite simple.  Calculate the volume of your home (square feet of floor space times average ceiling height) and use readily available formulas to determine the size of the fan you need.   Then cut a properly reinforced hole in your ceiling based upon the size of the fan you are using and mount the unit.  You also need to calculate and allow for the proper amount of roof venting. There are many pre-manufactured WHF units which can be found at big box stores and on the internet.

In our case, however, we ran into two snags during the planning phases of the project.  While our home has a relatively modest 2,383 square feet of floor space, our ceilings are 10 feet tall rather than the normal eight.   As a result, the volume of air we needed to move was larger than most typical homes and beyond the capacity of most lower cost WHFs.

Our second, and larger, problem was that whole house fans are designed to operate in a horizontal position.  Unfortunately, due to truss design and a maze of duct work, there was virtually no area in our attic where a “store bought” WHF could be mounted horizontally. 

As a result, we ended up designing and building our own vertical WHF.    We used a “drum fan” which is made to operate an a vertical position and has the additional benefit of moving large amounts or air at a lower cost than typical whole house fans.


 
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dewey302 (author) 1 month ago

Not sure my response to g1981c posted up correctly...so I'll try it again. Hopefully it doesn't appear twice now.

Looks like I need to go fan shopping. Fortunately, I was thinking about buying the identical fan I used in this project to cool my shop, which has no A/C. Based on g1981c's comments, I think I'll swap out the drum fan and move that out to the shop and then purchase a new dedicated exhaust fan that will work in the vertical position and mount it to the existing plenum.

Thanks for the info and education.

Dewey

g1981c1 month ago

what you may have not realized is that blower fans are not designed to work against a pressure gradient - they are designed to work in zero static pressure environment. using a blower fan as an exhaust fan is like using a sports car to tow a boat - a sports car may have more horsepower than a diesel pickup - that doesn't mean it will tow better, because it has lower torque and different transmission gearing. as such, your CFM / dollar calculations are somewhat meaningless because once the blower is placed in an exhaust fan application its CFM will plummet. it would be wiser IMO to use tools for their intended application and not to try and be smarter than engineers who designed them. i like your project overall - more fresh air, less electrical bills - but the choice of fan for the job i disagree with.

KCSCAMP1 month ago

I grew up in OH using an "attic fan"....and I just loved it...plus it was in my bedroom ceiling...
I went to sleep listening to the sounds.
I had a super little room with 2 doorways..I would shut one and get twice the air....YUM!
After I moved out my Dad added a fan at the end of the house too...so they had 2 attic fans...
I miss them....

Living in TX these past 31 years sure would have had a use for them!

damianzuch2 months ago

Hi Dewey, I bought a big drum fan years ago to help cool our shop down during the hotter summer days but we had a heat wave last summer and ended up taking it to the house and placing it at the foot of the bed at night. It almost takes the sheets off. I really like this system you have!

Hi, good one. have you considered increasing the thermal capacity? How's about epoxying ally soda cans end to nd
I'm not quite sure what you mean by thermal capacity? Are you referring to more mass inside the house to store heat/cold?
rimar20004 months ago
This is a very good idea.

I am using an old turbo fan, one of these cheap chinese, put in a hole at the attic wall. I turn on it in hot nights when the outer temperature lows, at late afternoon. It is very effective.
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