Are Whole House Fans Dangerous?

[James H. Bushart]

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.

Thoughts?

[Bruce A. King]

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

http://www.wholehousefan.com/consumeralert.html

http://ezinearticles.com/?The-Five-B...Fan&id=3341470

[Bob Elliott]

Too many variables.
No easy answer.

[Wayne B. Wilson]

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.

[Michael Larson]

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

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.

[Wayne B. Wilson]

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.

[James H. Bushart]

Originally Posted by mlarson

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.

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

[Joe Funderburk, CMI]

Originally Posted by jbushart

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

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.

Originally Posted by jbushart

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?

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

Originally Posted by jbushart

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

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

Originally Posted by jbushart

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

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

[Michael Larson]

Originally Posted by jbushart

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

The cable ran through a small tube.

Any air bypass was minimal.

[David A. Andersen]

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

If not, the fan will overheat and shut down.

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

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

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?

Smoke evacuation may save lives.

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

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.

[Wayne B. Wilson]

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.

[Bert B. de Haan]

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

Originally Posted by dandersen

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.

You're right. Cold air doesn't rise. I'm not sure what your point is though. 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.

[Wayne B. Wilson]

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

[ldapkus]

Originally Posted by mlarson

The cable ran through a small tube.

Any air bypass was minimal.

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

[James H. Bushart]

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.