# Whole House Fans



## Pete m. (Nov 19, 2011)

Vision49 said:


> Hi All,
> 
> 
> Is there anyone on the forum that has a lot of experience installing whole house fans. I have a good customer that would like a 24" direct drive whole house fan installed but the installation area has a double joist. I've installed maybe 8 whole house fans in the last twenty years but they all have been single joist mounted. I'm not sure if the having a double joist will allow the louver panel to be mounted.
> ...


How are the joists oriented? Why the double joist? Is it because a joist was cut and the header doubled to make up for it?

Pete


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## Vision49 (Feb 12, 2013)

Hi Pete,

The joists are running in the same direction as the pitch of the roof and there are two sets of double joist ....middle of the house. Looks like this is original to the construction of the home nothing has been cut or added. 
I'm sure I can do a joist mount of the fan and frame in the attic sitting on the double joist, it's the louvers I'm concerned with. I know from past experience the middle section just stay shut with the joist in installation while the louvers on the end open up from the draw of the fan. 
I just don't know if having a double joist will disallow the louvers from being mounted to the ceiling.


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## BT Electric (Feb 7, 2014)

The HO should look into a remote mounted whole house fan such as the Airscape Kohlio. They are much quieter than a direct drive ceiling mount and the lovers are mounted above the joists and the joists boxed in and sealed. Very easy install.


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## Vision49 (Feb 12, 2013)

Hi BT Electric,

That looks like a nice product. The CFM's aren't great,but I'm sure the noise level is much less than the standard direct/ belt drive whole house fan. Price of the unit may also be out of the budget always good to have options.


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## bkmichael65 (Mar 25, 2013)

You can always cut any joists in your way and brace them up with headers


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## Vision49 (Feb 12, 2013)

Hi bkmichael65,

I thought about that as well. In this case I would have to cut maybe 24"of one joist in the section where the louvers would go, leaving the second joist running down the middle. I'm not sure if this a very good idea and I don't want to create any structure problems. I think I would have to cut both joists in order to header them off.


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## bkmichael65 (Mar 25, 2013)

If you don't need to cut through both joists, I think you're fine to just cut out the section that's in the way and just attach the louvers and pick up your check. As long as one of the joists is intact, I wouldn't think there would be any structural problems that could arise


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## daveEM (Nov 18, 2012)

Like a Plumber baby. :thumbup::thumbup:

Now electricians are saying cut the joists out of your way.

Why would they have two? Sometimes we don't need to know everything. Especially about other trades. Just accept the fact someone decided two or double was required and keep your little hands off them.


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## Vision49 (Feb 12, 2013)

I don't think cutting out a section of one of the joists is a good idea:no:
not without re-supporting it.


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## 99cents (Aug 20, 2012)

Vision49 said:


> I don't think cutting out a section of the one of the joists is a good idea:no:
> not without re-supporting it.


Agreed. They didn't put in double joists because they had an extra one in the truck.

Cut up that joist and you will be the object of scorn on WoodButcherTalk.


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## Vision49 (Feb 12, 2013)

Not only that, but you could get yourself into financial or legal trouble.


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## MDShunk (Jan 7, 2007)

Careful. All this talk about cutting makes me nervous. Especially since people are saying ceiling "joist", but it may actually be (and more likely is) the bottom chord of a truss. Cut a truss and you just made scrap. Scrap that needs an engineer sealed detail print to prescribe the repair. Not as simple as adding a couple headers like some back yard deck project.


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## 99cents (Aug 20, 2012)

Funny how we trash other trades for minor indiscretions but we think it's okay for us to screw around with the structural integrity of a building. I have seen electricians who have hacked up lumber and, if it was my own house, I would sue the bastards.


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## bkmichael65 (Mar 25, 2013)

I really need to quit pulling answers out of my a$$. A little trip to the university of Google tells me that these joist were either doubled to provide extra strength to mount an air handler on or it is load bearing. It seems that some carpenters are comfortable with bracing the joist on the side opposite of the section that was cut out, while others say not to touch it without an engineers approval. Can the fan be mounted somewhere else?


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## dspiffy (Nov 25, 2013)

BT Electric said:


> The HO should look into a remote mounted whole house fan such as the Airscape Kohlio. They are much quieter than a direct drive ceiling mount and the lovers are mounted above the joists and the joists boxed in and sealed. Very easy install.


How are these different from a gable fan and ducting?

I presume with the lower CFM you could use more than one.


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## Vision49 (Feb 12, 2013)

I finally received some info. The louvers will not work across the double joists and there's no good way to modify them. 
I think installing the unit in a different location makes the most sense or installing a remote unit with ducting.


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## BT Electric (Feb 7, 2014)

The fan vents into the attic and not outside thus moving hot air out of the attic through the ridge vents, etc. This helps cool the house by lowering the attic temperature. As far as CFM's are concerned any volume of air the fan can move above what can be moved out of the vents is wasted. You can have a 5000CFM fan and only 2500CFM of venting area and the 2500 CFM is all that will be moved out if the attic. If the vent area is significantly larger then the airflow out of the attic will not be ideal and will not lower the temperature as well. The Airscape website shows how to calculate the venting that exists. 
I installed one last year and it has worked perfectly. I have enough vent area to move about 3000CFM which matches the fan very closely. 
Hope this helps!


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## bill39 (Sep 4, 2009)

BT Electric said:


> The fan vents into the attic and not outside thus moving hot air out of the attic through the ridge vents, etc. This helps cool the house by lowering the attic temperature.


BT is right about lowering the attic temperature. We love out whole house fan that is mounted in the hallway ceiling.

We rarely use the A/C in the evening except in the dog days of July & August.


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## dspiffy (Nov 25, 2013)

If the responses about "venting into the attic" were directed at my question, I meant, how is the construction of the fan different? In order words, couldnt you simply use a gable fan and some ducting in place of one of these remote mounted fans? That would give more options.

I havent seen whole house fans in a long time. They scared me as a kid. They work well, though, they really shouldnt have fallen out of popularity.


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## BT Electric (Feb 7, 2014)

Sorry dspiffy, I misunderstood your question! They are similar to a gable fan except the fan housing is suspended from jack chain instead of framed to the rafters like a gable fan. This isolates any fan vibration making it very quiet.


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## Fum Duck (Jan 2, 2011)

I didn't read much of the posts here, but I put one in my house and regret it. It will pull in an enormous amount of dust....


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