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Community and Q&A

Keep or remove whole house fan?

TimTuckerCom | Posted in General Questions on

Our house in SE Michigan has both AC and a whole house fan that I know is resulting in a huge loss of heat during the winter (and likely similar loss of conditioned air in the summer).

Currently we just have a sheet of R5 rigid foam screwed to the ceiling to block off the hole (ugly, but it works for now).

Currently debating between two options:
1. Remove the fan, drywall over the hole, & cover with insulation (less time & money, better insulation, less flexibility for cooling)

2. Create an insulated box over the existing fan w/ a linear actuator set to open the lid when the fan runs (more time & money, likely lower R value, leaves flexibility for cooling but introduces additional system complexity for maintenance)

Thinking things through, I wouldn’t put the fan in if I were building a new home — am I just falling into a trap of sunk costs with option #2?

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  1. swazo | | #1

    I like my whole house fan but part of that comes from enjoying fresh air and not needing AC often. (Minneapolis) I am planning on a whole house fan in a house we are building. In the summer with the AC on I believe the colder air drops down and isn't a problem. In the winter I put a "window kit" over the opening from the inside and built an insulated box with a cover over in the attic. It's a pain to climb up there twice a year. I should have hinged the cover with a rope to uncover.

    In the new house the fan will be in the end of a hall going into the space above the garage. It will have insulated doors on both sides to seal in winter.

    I think it depends on personal preference and life style. I wouldn't be without it.

    Hope this helps
    Jim Sweazey

  2. GBA Editor
    Martin Holladay | | #2

    We can't answer the question -- you have to. The most relevant question is, Do you ever use the fan?

    I'm skeptical that the idea of designing an insulated cap controlled by a "linear actuator" is going to be easy to build, troubleshoot, or maintain. If you like your whole-house fan, and want a good motorized insulated cap, buy a new Tamarack fan that includes the motorized cap.

    Here is a link: Tamarack whole-house fans.

  3. TimTuckerCom | | #3

    Admittedly I'm also skeptical that what looks pretty simple in the few Youtube videos I've seen of motorized covers will really be all that easy to build or a good idea in the long run.

    I've seen the Tamarack fans mentioned on the site in the past, but I'm not sure we'd get enough use out of one to justify the cost/benefit vs. just opening windows & running ceiling fans when we're in the room.

    What I guess I'm really looking for would be any additional data that might help drive the decision -- so far I'd come across an older NIST study that seems to suggest that would be a pretty viable strategy:

    "If the house temperature is to be maintained at a reasonably comfortable condition, the use of a whole-house fan could be substituted for that of an air conditioner whenever the outdoor temperature is less than about 82 °F."

    "The implication of this particular figure is that an equal or greater amount of cooling kWh savings can be obtained simply by increasing the cooling thermostat setting without even using a whole-house fan. For example, the annual cooling kWh reduction by whole-house fan at 78°F for the Washington D.C. ranch house is from 2500 kWh to 1900 kWh, or 600 kWh. Figure 23 shows that the same kWh savings can be obtained by simply turning the thermostat from 78° to 82°F. The comfort aspect at 82°F can be made similar to that of 78°F by using ceiling fan or similar room circulating fan as long as the room humidity level is not excessive."

    I haven't found much else that looked at use in similar climates (there's a Florida study that seems to be quoted often, but that doesn't look at all like our situation).

    So far the cons seem to be:
    - More effort involved to get savings than setting the thermostat for the AC to a higher temperature
    - Likely lower localized comfort than just using ceiling fans
    - Time / cost to box in (higher cost / complexity to create some type of automated solution vs. regular maintenance to open / close the box as needed)
    - Higher cost if replacing with a quieter, more efficient model (i.e.: one of the Tamarack units)
    - Too noisy to use the current fan at night (or for prolonged periods of time)
    - SE Michigan climate is often humid and not much cooler at night than during the day (for the days that we'd want extra cooling most), so it would be less effective
    - Potential risk of back-drafting with combustion appliances (gas dryer on the first floor, older gas furnace & gas hot water heater in the basement)

    - It's already there
    - Can quickly remove odors from the home

    It feels like either I'm missing something big or it should just be a no brainer to take it out and spend our money on improving air sealing & insulation in the attic.

  4. user-2310254 | | #4

    Martin has written so many great articles for this site he may have forgotten about this one. ;-)

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