Are Whole House Fans Dangerous?

Energy auditors write them up. Should home inspectors, too?

Consider the following:

  1. Creating a negative pressure inside the house draws in outside moisture and pollutants. (Crawlspace environments are actually sucked into the living space).

  2. Imagine a small fire starting in the home while the fan is on and the family is sleeping. Will the fan draw smoke past the smoke detection system too quickly to be detected while drawing more air for the flames?

  3. Is the attic adequately vented … not just for the excess moisture, but to expel 1200 to 2000 CFM?

  4. When they are off, they represent a penetration in the thermal boundary of the home and contribute to air leakage.


We should include something about them since most homeowners would not know.

Too many variables.
No easy answer.

I mention them, Due to the fact of sucking everything in through the home, Dangerous maybe , they could be wired with the smoke detectors to shut down during a fire.Also some of the fans weigh a lot in the event of a fire Firemen could be injuried not realizing they have them in older homes, there is really no benefit from them.

That depends how the are constructed.

I had one recently that had fully insulated hinged box cover over it in the attic that had to be opened using a cable in the laundry closet.

I explained the whole thing to my client.

That is the best way explaining it to the customer, Mention it on the report CYA.
Most people will not use them . Somewhat like a gas fireplace.

So…this one had an air bypass running through the wall into attic by way of the laundry closet.

Maybe put a sign beside the switch that says “Open the windows, Stupid!” With the windows open, I sincerely doubt anything from the crawl space gets drawn into the home. That would defy logic.

Do you have any evidence to substantiate the claim that a WH fan will cause the smoke detectors to fail to detect a fire?

As everyone knows, most homes built back in that day had large gable vents.

That is true. I include a comment advising them to build a thermally insulated enclosure when the fan is not in use.

The cable ran through a small tube.

Any air bypass was minimal.

If not, the fan will overheat and shut down.

It doesn’t draw it in and leave it there. It keeps on going right out the fan…

Smoke evacuation may save lives.

Yes they do, but mostly in the winter, not in the summer.
Cold air does not “rise”. As you know; there must be a pressure differential across a building opening to leak.

They should be sealed and insulated during the off season.

Your point about the smoke detector exists in most houses, even without the fan installed.

It also would spread fire faster . Positive pressure has been used in fire fighting for years Yes it clears the smoke , but you better be ready to snuff the source.Most of the ones Have seen have no insulation cover for the winter.
I just do not see the advantage of sucking Pollen and spores into your house.

  1. When they are off, they represent a penetration in the thermal boundary of the home and contribute to air leakage.

You’re right. Cold air doesn’t rise. I’m not sure what your point is though. :slight_smile: The warm house air will rise and go through the cracks into the attic.
I have never seen a whole house fan here. Maybe they are more common elsewhere.

You probably will never see one up then Ben Maybe in the big Smoke in TO

I’ve seen the same set up and a thermal scan indicated minimal air loss under negative pressure.

Thermal scans do not and can not measure amounts of air leakage.

Since air leakage accounts for 5% to 40% of space-conditioning loss and is usually found to be many small sources of leaks combining for the total AER, there is no such thing as an insignificant air leak. Sometimes, under certain conditions, air leaks can be seen by IR cameras…but they can never be measured by them.

Here’s the advantage. Turn off the AC. More money stays in your pocket. Less goes to the electric company.

You guys are too young. I grew up without AC. Open a window and enjoy the cool night air!

Ever seen a window fan? Works on the same concept.

Big difference of a window fan and a whole Fans are CFM Joe BTW i grew up also no AC and coal Heat and wood heat I am old too. I see no benefit . But that is my Thought only.

Whatever Mr. Energy Audit Overnight Pro.:p:p

In the evening, before going to bed we used to wedge a window fan in one window blowing out and in another window sucking in. About 10 minutes and the whole upstairs would be about 10 degrees cooler. A bit off topic but still somewhat relevant.

They are great in this part of the country especially if you don’t want to use so much expensive AC.

As the outside temp get about 75 or so open a low window or patio door, close the rest and let her rip.

Cools the house down quickly and reduces the AC for the next day.