Undersized vent fan - good for anything?

[JHZR2]

My one garage building has a 1000sf loft, no roof insulation, but it does have a ridge vent. The building is leaky, it is not climate controlled or sealed in any way.

In the last heat wave, it was super hot up there. Natural ventilation via the ridge vent wasn’t sufficient. Metal tools on the loft were hot to the touch, too hot to comfortably hold, and this was well into the evening after the sun wasn’t as strong.

So that brings me to airflow. Because of some work I did on the building, I have a few 3” holes through the upper walls.

This my idea - the $21 50CFM vent fan. I could install 1-4 of them, let’s say, and flow up to say 200cfm.

Sure there are much more expensive fans available, and of course ceiling fans or similar could also be used. But the $21 vent fan is… $21.

Yeah, I get it that it isn’t 5-6 air changes per hour, or 1cfm per sf, which are rules of thumb that I’ve seen.

But if I want to induce some air exchange to manage the heat levels in there under hot summer conditions, would this make sense?

Yes, I could put a box fan in a window. Blowing in, out, or through. But then I have wide open windows with fans in th. Not great when 4” of rain shows in an hour like we had yesterday…

Thoughts? Exercise in futility?

 

[dishdude]

That's like emptying the ocean with a teaspoon. Get a real attic fan or don't bother, those cheap 50 CFM fans can't even keep a small bathroom dry.

 

[Pablo]

That's like emptying the ocean with a teaspoon. Get a real attic fan or don't bother, those cheap 50 CFM fans can't even keep a small bathroom dry.

This.

 

[JohnnyG]

That's like emptying the ocean with a teaspoon. Get a real attic fan or don't bother, those cheap 50 CFM fans can't even keep a small bathroom dry.

Right.
Maybe just a good whole house fan, but I see they are much more expensive.
$279.00 @ Lowe's

https://www.lowes.com/pd/Cool-Attic...MI9p2hvPHAlQMVZIrCCB33sjNJEAQYBSABEgIE4PD_BwE

 

[AZjeff]

Less than 4 of your $21 fans and moves 2338 CFM. You need to draw replacement air from somewhere.


https://www.homedepot.com/pep/iLIVI...exDwHMc_8Yng3Jg370zxIkJqnSSamtpBoCr-EQAvD_BwE

 

[JHZR2]

That's like emptying the ocean with a teaspoon. Get a real attic fan or don't bother, those cheap 50 CFM fans can't even keep a small bathroom dry.

Problem with that logic is that when I put a 1700 cfm box fan on the window it stayed hot. Too much latent heat.

The key would be to just have it on a timer or run it continuously in advance to not let it get as bad as it was. But that said, perfect is the enemy of good enough.

Don’t really want/need to spend a ton, since it’s typically closed and unoccupied, and has been fine for over 100 years.

 

[dishdude]

I was thinking something more like this.

https://www.lowes.com/pd/Air-Vent-1...zed-Steel-Electric-Power-Roof-Vent/1000402231

 

[JHZR2]

You need to draw replacement air from somewhere.

The building is porous.

 

[JHZR2]

I was thinking something more like this.

https://www.lowes.com/pd/Air-Vent-1...zed-Steel-Electric-Power-Roof-Vent/1000402231

Hindsight is 20/20 I just did my roof and should have had one installed.

 

[Nukeman7]

My friend installed one of these through-the-wall fans near the peak of the gable end in his 20' x 16' stand alone un-insulated garage. It made a huge difference in the ambient temperature during the summer months.

iLIVING 18" Wall Exhaust Fan

 

[spasm3]

If its that hot, i don't think 200 cfm is going to do much of anything.

I would think about this.

https://a.co/d/00W3LG1e

 

[IndyIan]

If its that hot, i don't think 200 cfm is going to do much of anything.

I would think about this.

https://a.co/d/00W3LG1e

One of those in the peak of the roof should move a lot of air.
Is there lots of exposed steel roof on the interior side? I think with a steel roof, the thermal radiation from exposed steel will still heat up items in your attic. Maybe try a section of roof rafter channels, then the ridge vents will work better and there's much less thermal radiation too? Or just tack a roll of house wrap across all the rafters, might be cheaper and faster than rafter channels?

 

[Lubener]

If you already have a ridge vent, all you need is a sufficient amount of soffit type vents or something down low so that cooler outside air enters it and dispaces the hotter air exiting out the ridge vent.. You don't want to use a power ventillator fan up high along with a ridge vent.

 

[AZjeff]

The building is porous.

I put gable fan in our previous house. At the other end I put in several more gable vents to encourage the hottest air under the roof to go out the fan. You say it's a loft, you have to look at it and figure how to get the most hot air out. Letting air come from everywhere may not be the best way.

 

[JHZR2]

One of those in the peak of the roof should move a lot of air.
Is there lots of exposed steel roof on the interior side? I think with a steel roof, the thermal radiation from exposed steel will still heat up items in your attic. Maybe try a section of roof rafter channels, then the ridge vents will work better and there's much less thermal radiation too? Or just tack a roll of house wrap across all the rafters, might be cheaper and faster than rafter channels?

It’s not a steel roof. It’s a new shingle roof on new plywood decking.

Enclosing the rafters and roof would just make that part hotter/shorter life, no?

If you already have a ridge vent, all you need is a sufficient amount of soffit type vents or something down low so that cooler outside air enters it and dispaces the hotter air exiting out the ridge vent.. You don't want to use a power ventillator fan up high along with a ridge vent.

The building has a large opening to get up to the loft, and there are 8 x 3” holes drilled in the walls for some structural work I had done. It is cool downstairs.

Do I care if the ridge vent is doing anything but giving an exit path for the absolutely hottest air?

I put gable fan in our previous house. At the other end I put in several more gable vents to encourage the hottest air under the roof to go out the fan. You say it's a loft, you have to look at it and figure how to get the most hot air out. Letting air come from everywhere may not be the best way.

I’ve tried a fan in one window out the other. I’ve tried a fan up the stairs to the loft. I’ve tried windows open.

I think the key is that I’ve done all these things after the thermal mass got too hot. My key point is to keep enough ambient air coming in to provide some mixing and cooling, but not to much to introduce excess moisture, dust, etc.

 

[oilboy123]

I read something talking about putting a reflective material under the roof. They say the heat in say an attic like mine radiates through the roof then absorbs into the ceiling/insulation. Then that radiates through the ceiling into the house all day into the later evening. At which time it is dissipated. Then the next day rince repeat.

I have a standing seam roof with a ridge vent. Also sofit vents that seem OK on size. But the attic is a thermal nightmare when the the temp gets over mid 70s. I think the brown/bronze colorof the roof contributes to the heat.

I'm still researching this. I saw something that said installing right under the roof on sheathing would not work. That there needs to be an air gap, or it won't work. I would be installing on the roof framing under the roof sheathing. At least that is what I have been reading.

The below is something I'm looking into. I might still do other ventilation mods. It sounds like using the fan is getting rid of heat that has already been allowed to enter the attic. Where the reflective barrier is preventing the heat from ever entering the attic in the first place.


Try searching "Radiant barrier under roof reflective material"

:Reflective roofing insulation
Reflective roofing insulation is a reflective material installed at or near the roof deck to reduce heat transfer caused by solar radiation, functioning as a roof radiant barrier that helps control attic heat gain.

 

[vwmaniaman]

A gable vent fan helps a lot on the opposite end of the roof from prevailing wind. Wind helps to push out the heat.