Roof mount attic fan question

[3rdgendslmech]

The other day in the middle of our heatwave I noticed that the attic fan in the house was making some strange noises. Got up in the attic real quick and it sounded like the windings in the motor were going bad. Attic is around 1000 sqft.

When I first purchased the house the motor was locked up during inspection. So when I changed that motor out I just went to HD and bought a replacement motor. Didn't pay too much attention to detail but about 2 months later this motor had now failed. This time I bought a whole attic vent assembly. What I noticed was on the old original fan the pitch of the blades were different. So when I put in the second motor I put the fan in that matches it.

So today I open the new box, again, had to buy a whole attic fan assembly and I noticed that the new unit, the fan fits the opening better that what I have in my attic. New unit is 14" diameter, I dont know the opening in the house but it looks like the fan is too small for the opening. It still moves air pretty good.

At lowes and home depot all roof mounted fans are 14" but if you buy a gable mount you get a 18" fan. The only difference I see between a gable vs a roof mount is the mounting of the fan itself. If I have a 18" opening in my attic I'm guessing I could buy a gable mount fan, and remove it from the plastic mount and put it in my attic fixture?

 

[Red 17]

Probably. My roof vent and gable vent use the same motor. Bought one at Grainger, then one on line. Numbers were right on the motor. I've seen the "buy the whole thing and throw away the stuff you don't need" approach.

 

[3rdgendslmech]

Probably. My roof vent and gable vent use the same motor. Bought one a Grainger, then on line. Numbers were right on the motor. I've seen the "buy the whole thing and throw away the stuff you don't need" approach.

Yeah that's what I ended up doing with the 2nd one I put in like 7 years ago. Feel like a hell of a waste of metal throwing away a whole lid like that.

Im gonna measure the opening tomorrow but i'm willing to bet I should be using at 18" fan

 

[SGKent]

I never had any luck with those fans lasting. The solution I came up with was to add additional venting to the house on the gable ends and on the soffits, and it is cooler now than when there was a roof fan. My neighbor uses the whirlybird things but every few years one blows off in a wind storm. I added the venting for a whole house fan and it helped with everything else. Also when it is early morning I can turn the whole house fan on and blow the whole attic out. Triangle Fans are really good. http://trianglefans.com/whole-house-fans/ They also make other kinds of fans for venting.

 

[glend123]

My attic fan was always too loud/ vibrating. 2nd one was similar. When i had my roof replaced I just got rid of it. seems just as hot up there now as with the fan.

 

[strutaeng]

I thought most people realized these things were not a good idea by now?

Based on common sense, they seem like they are a good idea, but this article may prove otherwise:

https://www.greenbuildingadvisor.com/article/fans-in-the-attic-do-they-help-or-do-they-hurt

 

[yeldogt]

Remember -- in many cases the attic is cooler because it's drawing in the cool air from the house ... negative pressure. Also bad in any radon area. Plus the cost of running the motor.


They can also create problems with moisture in green grass climates.

 

[Stuart in MN]

Is the existing attic fan vertical or horizontal? The bearings may not last on a gable fan (which is designed to operate horizontally) that's used in a vertical orientation.

 

[3rdgendslmech]

Is the existing attic fan vertical or horizontal? The bearings may not last on a gable fan (which is designed to operate horizontally) that's used in a vertical orientation.

It's mounted on a 4/12 pitch roof. So vertical.

 

[yeldogt]

Also -- In NJ when they do an energy audit to qualify for the rebate and 0% loan .. you have to take them out.

 

[bad_idea]

Is the existing attic fan vertical or horizontal? The bearings may not last on a gable fan (which is designed to operate horizontally) that's used in a vertical orientation.

What he said. Motors have to be designed with proper bearings to be used in a vertical position. This article covers the differences pretty well: https://www.efficientplantmag.com/2018/04/understand-vertical-motor-bearings/

 

[BigGarage]

Is the existing attic fan vertical or horizontal? The bearings may not last on a gable fan (which is designed to operate horizontally) that's used in a vertical orientation.

What he said. Motors have to be designed with proper bearings to be used in a vertical position.

I found this out the expensive way. I bought a 28" whole-house attic fan and mounted it vertically in my enclosed rear porch. The box (Home Depot) did not have info about how it should be mounted (or not be mounted) but when I went online and found the same fan it specifically said mount it only horizontally.

It lasted 1 1/2 summers and then I spent (just checked) $266.89 on a motor with the correct bearings for vertical mount. It's nice to have on warm but not real hot days.

Dennis

 

[rshadd]

I just replaced my roof a few weeks ago and every roofer ( I got 14 estimates) recommended removing the existing attic fan and installing a ridge vent.

 

[SGKent]

I just replaced my roof a few weeks ago and every roofer ( I got 14 estimates) recommended removing the existing attic fan and installing a ridge vent.

that is a good solution too. My folks had one on their home and it was installed right. Weathered 3 hurricanes without leaking.

 

[Red 17]

My house has vents under the eaves, so the idea that I'm pulling the interior air into the attic does not apply to all houses.

And in the relentless heat waves of mid summer, there is no cool air to pull into the house via the whole house fan method.

YMMV

 

[yeldogt]

My house has vents under the eaves, so the idea that I'm pulling the interior air into the attic does not apply to all houses.

And in the relentless heat waves of mid summer, there is no cool air to pull into the house via the whole house fan method.

YMMV

They still create negative pressure -- air pressure is not equal across the space. Air does not know that it supposed to come trough the the vents.

Also the free area nor the static pressure of the vents ever works out w/ what the fan moves w/o resistance.