# Are Whole House Fans Dangerous? **URL:** \ **Category:** Inspecting HVAC Systems\ **Created:** [July 31, 2010, 2:39am UTC](https://forum.nachi.org/t/are-whole-house-fans-dangerous/51434 "2010-07-31T02:39:51Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![jbushart](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@jbushart](https://forum.nachi.org/u/jbushart)\ **Post date:** [July 31, 2010, 2:39am UTC](https://forum.nachi.org/t/are-whole-house-fans-dangerous/51434/1 "2010-07-31T02:39:51Z")
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? ---
**Author:** ![bking](https://sea2.discourse-cdn.com/internachi/user_avatar/forum.nachi.org/bking/32/624_2.png) [@bking](https://forum.nachi.org/u/bking)\ **Post date:** [July 31, 2010, 3:36am UTC](https://forum.nachi.org/t/are-whole-house-fans-dangerous/51434/2 "2010-07-31T03:36:17Z")
We should include something about them since most homeowners would not know. [http://www.wholehousefan.com/consumeralert.html](http://www.wholehousefan.com/consumeralert.html) > **[The Five Biggest Mistakes Home Owners Make When Installing a Whole House Fan](https://ezinearticles.com/?The-Five-Biggest-Mistakes-Home-Owners-Make-When-Installing-a-Whole-House-Fan&id=3341470)** > > This article outlines some very important points you should think about before putting in a whole house attic fan. It also explores the most common mistakes that do-it-your-selfers make when choosing a whole house attic fan, AND good solutions you... ---
**Author:** ![belliott](https://sea2.discourse-cdn.com/internachi/user_avatar/forum.nachi.org/belliott/32/57038_2.png) [@belliott](https://forum.nachi.org/u/belliott)\ **Post date:** [July 31, 2010, 9:15am UTC](https://forum.nachi.org/t/are-whole-house-fans-dangerous/51434/3 "2010-07-31T09:15:25Z")
Too many variables. No easy answer. ---
**Author:** ![wwilson3](https://sea2.discourse-cdn.com/internachi/user_avatar/forum.nachi.org/wwilson3/32/58197_2.png) [@wwilson3](https://forum.nachi.org/u/wwilson3)\ **Post date:** [July 31, 2010, 10:40am UTC](https://forum.nachi.org/t/are-whole-house-fans-dangerous/51434/4 "2010-07-31T10:40:33Z")
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. ---
**Author:** ![mlarson](https://sea2.discourse-cdn.com/internachi/user_avatar/forum.nachi.org/mlarson/32/89225_2.png) [@mlarson](https://forum.nachi.org/u/mlarson)\ **Post date:** [July 31, 2010, 11:07am UTC](https://forum.nachi.org/t/are-whole-house-fans-dangerous/51434/5 "2010-07-31T11:07:00Z")
> [@](#): > > 1. 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. ---
**Author:** ![wwilson3](https://sea2.discourse-cdn.com/internachi/user_avatar/forum.nachi.org/wwilson3/32/58197_2.png) [@wwilson3](https://forum.nachi.org/u/wwilson3)\ **Post date:** [July 31, 2010, 11:32am UTC](https://forum.nachi.org/t/are-whole-house-fans-dangerous/51434/6 "2010-07-31T11:32:37Z")
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. ---
**Author:** ![jbushart](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@jbushart](https://forum.nachi.org/u/jbushart)\ **Post date:** [July 31, 2010, 1:37pm UTC](https://forum.nachi.org/t/are-whole-house-fans-dangerous/51434/7 "2010-07-31T13:37:26Z")
> [@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. ---
**Author:** ![jfunderburk](https://sea2.discourse-cdn.com/internachi/user_avatar/forum.nachi.org/jfunderburk/32/187920_2.png) [@jfunderburk](https://forum.nachi.org/u/jfunderburk)\ **Post date:** [July 31, 2010, 2:02pm UTC](https://forum.nachi.org/t/are-whole-house-fans-dangerous/51434/8 "2010-07-31T14:02:55Z")
> [@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. > [@jbushart](#): > > 1. 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? > [@jbushart](#): > > 1. 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. > [@jbushart](#): > > 1. 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. ---
**Author:** ![mlarson](https://sea2.discourse-cdn.com/internachi/user_avatar/forum.nachi.org/mlarson/32/89225_2.png) [@mlarson](https://forum.nachi.org/u/mlarson)\ **Post date:** [July 31, 2010, 2:12pm UTC](https://forum.nachi.org/t/are-whole-house-fans-dangerous/51434/9 "2010-07-31T14:12:23Z")
> [@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. ---
**Author:** ![dandersen](https://sea2.discourse-cdn.com/internachi/user_avatar/forum.nachi.org/dandersen/32/59398_2.png) [@dandersen](https://forum.nachi.org/u/dandersen)\ **Post date:** [July 31, 2010, 3:25pm UTC](https://forum.nachi.org/t/are-whole-house-fans-dangerous/51434/10 "2010-07-31T15:25:42Z")
> [@](#): > > 1. 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… > [@](#): > > 1. 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. > [@](#): > > 1. 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. ![](https://global.discourse-cdn.com/internachi/original/4X/c/4/1/c41726fa43ed97f41c31b24e450eeb3d22c23d0c.jpeg) ---
**Author:** ![wwilson3](https://sea2.discourse-cdn.com/internachi/user_avatar/forum.nachi.org/wwilson3/32/58197_2.png) [@wwilson3](https://forum.nachi.org/u/wwilson3)\ **Post date:** [July 31, 2010, 8:59pm UTC](https://forum.nachi.org/t/are-whole-house-fans-dangerous/51434/11 "2010-07-31T20:59:45Z")
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. ---
**Author:** ![bdehaan](https://avatars.discourse-cdn.com/v4/letter/b/eada6e/32.png) [@bdehaan](https://forum.nachi.org/u/bdehaan)\ **Post date:** [July 31, 2010, 9:54pm UTC](https://forum.nachi.org/t/are-whole-house-fans-dangerous/51434/12 "2010-07-31T21:54:41Z")
1. When they are off, they represent a penetration in the thermal boundary of the home and contribute to air leakage. > [@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. ---
**Author:** ![wwilson3](https://sea2.discourse-cdn.com/internachi/user_avatar/forum.nachi.org/wwilson3/32/58197_2.png) [@wwilson3](https://forum.nachi.org/u/wwilson3)\ **Post date:** [July 31, 2010, 9:58pm UTC](https://forum.nachi.org/t/are-whole-house-fans-dangerous/51434/13 "2010-07-31T21:58:35Z")
You probably will never see one up then Ben Maybe in the big Smoke in TO ---
**Author:** ![ldapkus](https://sea2.discourse-cdn.com/internachi/user_avatar/forum.nachi.org/ldapkus/32/58272_2.png) [@ldapkus](https://forum.nachi.org/u/ldapkus)\ **Post date:** [July 31, 2010, 11:21pm UTC](https://forum.nachi.org/t/are-whole-house-fans-dangerous/51434/14 "2010-07-31T23:21:32Z")
> [@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. ---
**Author:** ![jbushart](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@jbushart](https://forum.nachi.org/u/jbushart)\ **Post date:** [August 1, 2010, 12:20am UTC](https://forum.nachi.org/t/are-whole-house-fans-dangerous/51434/15 "2010-08-01T00:20:48Z")
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. ---
**Author:** ![jfunderburk](https://sea2.discourse-cdn.com/internachi/user_avatar/forum.nachi.org/jfunderburk/32/187920_2.png) [@jfunderburk](https://forum.nachi.org/u/jfunderburk)\ **Post date:** [August 1, 2010, 12:28am UTC](https://forum.nachi.org/t/are-whole-house-fans-dangerous/51434/16 "2010-08-01T00:28:46Z")
> [@wwilson3](#): > > I just do not see the advantage of sucking Pollen and spores into your house. Here’s the advantage. Turn off the AC. More money stays in your pocket. Less goes to the electric company. [![](https://www.indiatone.com/wp-content/uploads/2010/04/100-dollar-bill.jpg) ](https://www.indiatone.com/wp-content/uploads/2010/04/100-dollar-bill.jpg) 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. ---
**Author:** ![wwilson3](https://sea2.discourse-cdn.com/internachi/user_avatar/forum.nachi.org/wwilson3/32/58197_2.png) [@wwilson3](https://forum.nachi.org/u/wwilson3)\ **Post date:** [August 1, 2010, 1:25am UTC](https://forum.nachi.org/t/are-whole-house-fans-dangerous/51434/17 "2010-08-01T01:25:12Z")
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. ---
**Author:** ![ldapkus](https://sea2.discourse-cdn.com/internachi/user_avatar/forum.nachi.org/ldapkus/32/58272_2.png) [@ldapkus](https://forum.nachi.org/u/ldapkus)\ **Post date:** [August 1, 2010, 1:26am UTC](https://forum.nachi.org/t/are-whole-house-fans-dangerous/51434/18 "2010-08-01T01:26:44Z")
> [@jbushart](#): > > 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. Whatever Mr. Energy Audit Overnight Pro.:p:p ---
**Author:** ![bdehaan](https://avatars.discourse-cdn.com/v4/letter/b/eada6e/32.png) [@bdehaan](https://forum.nachi.org/u/bdehaan)\ **Post date:** [August 1, 2010, 1:29am UTC](https://forum.nachi.org/t/are-whole-house-fans-dangerous/51434/19 "2010-08-01T01:29:02Z")
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. ---
**Author:** ![mlarson](https://sea2.discourse-cdn.com/internachi/user_avatar/forum.nachi.org/mlarson/32/89225_2.png) [@mlarson](https://forum.nachi.org/u/mlarson)\ **Post date:** [August 1, 2010, 1:32am UTC](https://forum.nachi.org/t/are-whole-house-fans-dangerous/51434/20 "2010-08-01T01:32:52Z")
> [@wwilson3](#): > > 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. 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. [Next page](https://forum.nachi.org/t/are-whole-house-fans-dangerous/51434.md?page=2)