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gt500 · Jul 14, 2005, 04:11 PM

I recently installed a wall mounted exhaust fan (about 260 cfm) in a 2 car garage in Arizona (20x20x10high). I run this fan periodically to remove exhaust fumes and to suck out hot air. My garage is fairly tight as far as the seals are concerned and I've determined that I need a fresh air vent in order to replace the air I'm drawing out with the exhaust fan. I also have a gas fired water heater in the garage that cuts out occasionally because it doesn't have any oxygen to run (I'm assuming that is the case) as I've drawn it all out with the fan.

My questions are what size fresh air vent do I need? Also, is there a product out there that I can use to install in the wall easily as one piece. Ideally, I would like something with a filter, vents that can be closed when it is cold, and a screen to keep out critters and bugs.

labman · Jul 14, 2005, 09:26 PM

I would look at foundation vents. They present a finished appearance, are screened, and some can be closed. I would trust myself more than the thermostatically controlled ones, and buy a manual one. My furnace needs 40 square inches free opening. The foundation vent I installed in my crawl space for it was rated at 50 sqin, which should be more than enough for the hotwater heater. However, I have no idea how adequate it would be for the fan. You could try adding one, and if you still had problems, add a second.

Frank Mangrum · May 13, 2012, 03:10 PM

Originally Posted by gt500

I recently installed a wall mounted exhaust fan (about 260 cfm) in a 2 car garage in Arizona (20x20x10high). I run this fan periodically to remove exhaust fumes and to suck out hot air. My garage is fairly tight as far as the seals are concerned and I've determined that I need a fresh air vent in order to replace the air I'm drawing out with the exhaust fan. I also have a gas fired water heater in the garage that cuts out occassionally because it doesn't have any oxygen to run (I'm assuming that is the case) as I've drawn it all out with the fan.

My questions are what size fresh air vent do I need? Also, is there a product out there that I can use to install in the wall easily as one piece. Ideally, I would like something with a filter, vents that can be closed when it is cold, and a screen to keep out critters and bugs.

I would be more concerned with what is going on with the waterheaters exhaust gases when it is operating along with the exhaust fan. Do you operate the exhaust fan with the doors closed in the garage? If so you could most likely be pulling exhaust gases from the water heaters flue into the room which contains carbonmonoxide if the water heater has an open draft hood and using garage air as combustion air to water heaters burners. If this is the case, this exhaust fan should not be used at all in this environment- Remember carbonmonoxide is deadly!