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Old 10-21-2009, 10:41 AM   #1
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Garage Ventilation Question

I am new here just having found this site, but I am amazed at the information here and the willingness to guide DIYers in the right direction. Glad I found the site as I am about to start a basement finishing job soon and I have already found answers to some questions that I had. Now to my current questions;

I have a 26X28 attached garage at my house. The garage walls are insulated along with having insulated doors. The walls are sheetrocked, painted and has baseboard so really a finished look. The house is 8 years old. There is no HVAC run to the garage area and no return there.

In the summer when it is hot outside and we pull a vehicle into the garage, the heat from the engine just adds to the heat already in the garage and it makes it really hot in there. It will stay hot long into the night with the heat coming from two warm vehicles and I am sure that a certain amount of that heat transfers into the house through the walls.

I had thoughts of installing some type of roof ventilation fan inside the garage, possibly operated by a thermostat which would come on at a preset temperature, then shut off once a comfortable level is reached. I also have a pull down staircase in the garage and a floored 16X28 area overhead so access to this area is in place. I do also have a constant roof ridge vent which is easily seen from this floored area. Access to the area directly over the garage is good and electricity to this area is already there for 120 volts that operates lighting for the floored area.

Iíd like some thoughts on this, and if for some reason I havenít thought of, tell me if this is a bad idea. If itís a good idea some recommendations on what size of exhaust fan/thermostat would be needed to ventilate the area. Iím much more concerned with the excessive heat than anything. We never have the cars running any longer than necessary inside the garage and we always leave the doors open a short time to exhaust the car fumes before closing them. In the winter this isnít really a problem, but here in North Carolina it stays warm to down right hot about 8-9 months of the year. Thanks for any advice you could give on this.


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Old 10-22-2009, 09:02 AM   #2
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Just so you know you're not crazy, I have the same problem

My 3 car attached garage is finished the same as yours and when you open the door to the garage in the evening you can feel the heat.

I have a bonus room above the garage so it's not easy for me to add a fan of any kind.

I wonder if you could add a bathroom exhaust fan? Not sure how you would run it based on the temperature though.



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Old 10-22-2009, 12:51 PM   #3
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Years ago (30) the FHA used to require a 4x16" inlet on a low sidewall in the garage. And the same size outlet on the high opposite sidewall, near the big garage door to let fumes (exhaust ) escape. I see this is no longer required by them now. They sell specific exhaust garage fans now. I would ask your local building department about them. They may have to be flash resistant (remote motor), like in automotive paint spraying, but I do not know. Be careful if you have any gas appliances (furnace, hot water tank, etc.) when using forced ventilation, to not draw the pilot light flame out. Long after parking the water on a hot car turns to moisture vapor in the cooler air and wants to go to the warmer house walls.This is similar to venting an attic with a fan which also can cause problems: My point being, research this and please let us know how your solution works.
Be safe, Gary
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17,000 dryer fires a year, when did you last clean the inside of the dryer near motor or the exhaust ducting?
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Old 10-22-2009, 07:06 PM   #4
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Thanks for the replies. I have spoken to a building inspector by phone and he is willing to come by and look at my situation to try and make proper suggestions. I will report his suggestions once he gets a chance to visit.

Some good points brought out in the previous posts so I'll ask some specific questions to the inspector on those. Hopefully he will get by within the next week. If there are any other suggestions keep them coming.

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Old 10-22-2009, 07:10 PM   #5
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Do you have soffit vents that ventilate the area over the garage?
Anu insulation w/venting against the roof rafters to keep the days heat from entering this space?
How much insulation between the garage & the attic area?
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Old 10-22-2009, 09:24 PM   #6
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With an engine being 30% efficient, you might have to dissipate 25 kw at first, dwindling down to nothing in a few hours.
How quickly do you want the air to cool how many degrees? In principle, knowing the specific heat of iron and air, the CFM req'd could be calculated.

Or you could add a wall between the house wall and the garage and move outside air just through the space between your wall and the house wall with a small fan. Internal 1x2 partitions would route the moving air in a serpentine path; like a heat exchanger. In effect, you'd have a wall that insulates perfectly as long as the fan runs.


Last edited by Yoyizit; 10-22-2009 at 10:19 PM.
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