Solar Attic Fan and expected temperature reduction

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Old 05-28-20, 07:02 AM
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Solar Attic Fan and expected temperature reduction

I have 3rd car garage that has been re-purposed as a media room, and so I'm trying to see if a roof mounted attic fan will help reduce the temperature in this room during summer months. Some details about the garage and attic above:

- Approx size - attic is for 3-car garage so roughly 20x30 or 600 sq. ft.
- Garage is finished throughout with drywall - no exposed beams on ceiling or walls
- There is a wall built out between the 2car and 3rd car portions of the garage - and a door of course. Also there is a 'fake wall' covering the garage door on the inside 3rd car part, which adds some level of insulation but is mostly there for esthetics
- Garage ceiling is about 8.5'
- The attic roof is pitched and at peak is about 4f't from the ceiling.
- Currently there are no vents at all - there are 2 solatubes in the attic but nothing to drive hot air out of the space. The garage firewall separates the garage attic from the main attic for the house (which has several vents)
- Garage faces due north, so primarily gets afternoon/evening sun
- There is 'some' insulation above the 3rd car garage portion of the attic where I have the media room
- I live in coastal Southern Calif

The insulation in the 3rd car garage/media room walls/ceiling is definitely helpful, also this room is towards towards the inner part of the house and doesn't have an external wall taking the afternoon sun. I haven't measured the temperature difference but I'd guess at least 5-10 degree difference when the sun is hitting the garage in the afternoon - between the 2car and 3rd car portions of the garage. Anyhow - sorry for the details but thought I'd be thorough..

Any thoughts on how much temperature cooling you'd expect from one of these Roof Mounted attic fans is greatly appreciated
 
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Old 05-28-20, 07:49 AM
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I do not think you will gain much if anything with just a roof fan.
You also need a way for air to get into the garage attic either a gable vent or soffit vents.

Before I did anything I would get one of those hand held remote temperature sensing guns. They are fairly cheap.
Then find out where the hot spots in the room are.

 
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Old 05-28-20, 08:32 AM
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Currently there are no vents at all
Are you sure about this? Unless you have insulated roof, your house is built wrong.
There should be vents at soffit for intake and gable or ridge vent for exhaust.

Attic fan won't help much if there are no intakes. Without proper intake, it will just pull air from conditioned space through any gap it can find.

Install some vents at soffit, then either install ridge vent or attic fan. It will help a lot if your attic was not properly vented as you say.
 
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Old 05-28-20, 09:00 AM
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Thanks Manden - and yeah I have some temperature sensors so I can track things throughout the day in this 3rd car garage media room.. So far this month isn't bad but come July/August it'll probably be upwards of 95F or so in this room.

I get your point though - I need some type of an intake of cooler air in addition to something forcing out hot air.. Since I am using this space as a media room, I have already blocked out the 2 Solatubes to minimize ambient lights.. Maybe I get a roofing contractor to remove the Solatubes - replace one with a Soffit vent and the second one with a Roof Mounted Fan? There isn't a side wall to support the gable vent on the side of my garage so my only option is the Roof.

 
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Old 05-28-20, 09:36 AM
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@lambition - I will double-check this in terms of vents - the home was built in 1968. There was an addition done in the 90's or so - this added square footage behind the garage and the construction made the roof pitch higher to accommodate extending the roof for new square footage. The firewall between garage and house didn't move but got taller..
 
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Old 05-28-20, 11:26 AM
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You cannot use your solar tube hole as intake. That is too high. Depending on how high it was mounted, might not be suitable for exhaust either.
Soffit vents go on the soffit. If you will be hiring roofing contractors, ridge vent might be a better solution. It is a passive venting that doesn't require any fan. Usually that is enough for most houses.

This is the basic idea.

 
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Old 05-28-20, 12:17 PM
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Ok gotcha @lambition. I was confusing Soffit vents with Dormer vents.. Though turns out the garage has neither. I do see some 'soffit-like' vents (see attached image) under the eaves for the non-garage living spaces. However, there are currently none of these in this garage portion of my house. So no air intake or exhaust.

BTW - the room addition I was referring to is pretty interesting. As I mentioned the roof-line of the house was raised to cover the additional sq footage. However, the old roof line is still intact within the attic

 
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Old 05-28-20, 03:01 PM
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You seem fixated on a fan.
I do not know how much advantage it would give you.
Hot air rises so as shown in lambition's drawing it removes hot air from the attic naturally
The money is probably better spent on more insulation.
Also insulating those solar tubes
 
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Old 05-28-20, 03:30 PM
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Haha - not so much fixated as uneducated.. I guess I was mostly looking at that since I've got the holes in my roof already due to the Solatubes. Rather than make new holes in my roof I was hoping to replace one of the Solatubes with a roof mounted fan or maybe a Dormer vent.

But you guys have convinced me that it won't do much unless I can get some cooler air into the space first. For starters, I'm gonna beef up the insulation over the 3rd car garage and also see about adding some of those vented sections under the eaves of my garage
 
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Old 05-29-20, 07:02 AM
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You might be able to replace the solatube with a fan & add a dormer vent for intake. You would have to remove the tube & patch the ceiling.
 
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Old 05-29-20, 09:24 AM
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Kinda thinking - as my goal is to try to get this converted 3rd car garage room cooler - plus it sounds like the lack of ventilation in the attic is a code violation and could result in mold? .. Maybe the following makes the most sense:
  • Dormer Vent - provides much-needed exhaust/ventilation in the attic - hopefully replace a Solatube to minimize more holes in my roof
  • Whole House Fan - Intake in the ceiling of the 3rd car garage - can pull cooler air into room and force into the garage attic
 
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Old 05-29-20, 12:18 PM
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I don't know how high your existing solar tubes are, but if they are not high enough (close to the ridge), it may not to much good. It still needs a intake to actually circulate air in the attic.

If your roofing is not too old, it won't be too hard to repair the hole and still match the color.
I have 10+ years old roofing, when I removed chimney I was able to find exact same shingles at roofing store. Existing roofing has gotten much darker from years of dusts and mold. After bleaching and some scrubbing, I was able to match the color good enough. Not so noticeable.

Poorly ventilated attic can result in mold, but it really depends on your area. If you live in dry area, mold is unlikely to grow.

Whole house fan is good for ventilation of whole house. But, that is not for keeping the house cool.
It is a good option when not running AC, but you want to keep cool air inside when you are running AC.
 
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Old 05-29-20, 02:33 PM
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@lambition - good callout reg'd the whole house fan. They are great during the evening/night but I wouldn't be running it during the hot parts of the day - so other ventilation would be preferred.

Posting a satellite aerial view of my house - I also added some lines/text to show the Solatubes, Garage, and the Room Addition done a while back.. The section between the Room Addition and Garage is where the roof-line was changed, so there are some internal structures from the old roof-line in there. That main external roof 'Apex' at the back of the garage is not actually visible from inside the attic due to the internal roof structures from the original home build-out.. I'd estimate the internal apex as seen from inside the garage attic is close to the end of the overlay text 'Garage'.

A couple of other callouts - I am in Southern Cal coastal - so we don't get too hot or too humid
 
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Old 05-29-20, 03:33 PM
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You might be able to replace the solatube with a fan
I had one of these a couple houses ago, the way they are installed is like a roof vent, you would have to tear up a good portion of the shingles just to get the bubble off, there is no frame that a fan would attach too,

I just dont see this as a viable solution.
 
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