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Safety -- Make sure you are safe! |
2011-12-04, 9:44pm
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Member
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Join Date: Nov 22, 2011
Posts: 45
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Garage ventilation and gas water heater
Hi all,
I've read so many threads here and think I have a handle on the exhaust system I want to install in my garage. It will be on the far side of a two car garage from my gas water heater and dryer, vented outdoors, directly through the wall. I have one question, and please forgive me if it's already been answered, but I couldn't find it.
Do I have to worry about a 600-1000 cfm squirrel cage fan pulling the exhaust from the dryer and water heater across the room?
Thanks for any opinions.
Cheryl
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2011-12-05, 8:20am
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Gentleman of Leisure
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Join Date: Jun 10, 2005
Location: A Little Bit West of Yosemite Valley
Posts: 5,200
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Quote:
Originally Posted by Cherylka
Hi all,
I've read so many threads here and think I have a handle on the exhaust system I want to install in my garage. It will be on the far side of a two car garage from my gas water heater and dryer, vented outdoors, directly through the wall. I have one question, and please forgive me if it's already been answered, but I couldn't find it.
Do I have to worry about a 600-1000 cfm squirrel cage fan pulling the exhaust from the dryer and water heater across the room?
Thanks for any opinions.
Cheryl
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Yes... The solution is to have a large source (volume) of makeup air (assuming large door will be closed most of the time) so there is less of a chance of "flue reversal" in water heater vent....
Dale
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San Francisco - A Few Toys Short of a Happy Meal
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2011-12-05, 9:19am
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Member
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Join Date: Nov 22, 2011
Posts: 45
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Thanks for responding so quickly Dale, I really appreciate your expertise and willingness to help.
If I open the roll-up garage door 6-8 inches while I torch will that do it? My walk in door is next to the exhaust fan. Great for walking out to turn off the propane tanks which will be outside, but not for makeup air.
If the roll up isn't sufficient, the alternative I can fairly easily do is install a small window in the wall next to the garage door.
I also plan to install a CO monitor as a bit of insurance.
Thanks again.
Cheryl
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2011-12-05, 11:33am
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Curmudgeon Engineering
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Join Date: Feb 15, 2006
Location: Near Seattle, WA
Posts: 1,723
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The CO monitor is always a good idea. The window is also a good option if for some reason you don't want to use the rollup. The rollup should give sufficient volumn of makeup to prevent pulling the gas appliance exhaust into the garage.
To check it out fire up your vent system with the rollup open to where you think it should be enough, light your torch, then peek into the water heater chamber and observe the pilot light or the flame when it is running and see if the little candles are flickering or are leaning toward to opening such as if they would be if they were being sucked toward the opening. Some gas appliance vents have a little triangular 'hat' thing in the vent pipe just above the heater. Hold a sheet of tissue paper near this and see if it is sucked toward the pipe (good) or away (bad) and open your roll up more to compensate.
That sounds backwards but the reasoning is; when running normally the WH vents hot gas up the pipe. This hot gas will cause some air outside the pipe to be sucked into the pipe via the little triangular thing (sorry I don't recall it's name). If your vent system is drawing air or gases from the WH vent pipe then the tissue will be pulled away from the pipe.
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2011-12-08, 11:59am
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Member
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Join Date: Nov 22, 2011
Posts: 45
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OK, I think I have that part down. Now another question... It seems there is a sea of information out there. I am having a hood built by a metal guy and can have basically anything I can afford.
If I do a barley box type hood, is there an "ideal" dimension? Several people talked about feeling claustrophobic working in these, but one also mentioned having to add the sides later because of flame stability issues.
If I go with a standard "Hanging Hood" type arrangement, am I asking for trouble with cross ventilation later (using garage door for makeup air)? It sounds like there might be issues with the vapors being blown sideways before they get up to the hood, if I read and processed the info correctly.
If I do use the hanging hood, is there an ideal size for that?
Thanks again for your input. I'd hate to have this thing built and then find it won't work.
Cheryl
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2011-12-08, 12:16pm
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Curmudgeon Engineering
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Join Date: Feb 15, 2006
Location: Near Seattle, WA
Posts: 1,723
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In my opinion;
The hood size is dictated by the bench size. I like to have about 6" to 8" more bench than hood if that makes sence. Ie. if the bench is against the wall and 48" deep to the wall then the hood would be 42" to 40" deep. The width is determined by the working envelope of your work area. It should be wide enough to cover a comfortable span. As for the sides they can be full coverage of modified such as mine below.
Imagine the end of your vacumn cleaner hose. The air rushing in comes from all around the opening. As you get farther from the opening the air slows down and looses force. The air being sucked up is made up from all directions also. Problems with cross ventilation are not common but problems with eddy currents and swirly currents are. That's one of the main reccommendations for side 'curtins'.
You can see my sides are about 6" shallower than the bench and are triangular. They are also removable so I can set up torches on the end of the bench. The bottom edge of the hood is just below the top of my head.
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