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Inspecting HVAC Systems Topics include heating, venting, and air conditioning inspections.

 
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  #1  
Old 1/3/08, 11:01 AM
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Default Draft fan & gravity vent

I know that I have run across this before and never thought about it, but yesterday I ran across 3 draft fan induced furnaces and a gravity vent water heater connected to the same flue. The flue size looked OK (was bigger at each connection). It got me thinking though, that couldn't the draft fans cause a back draft at the water heater draft diverter. I don't recall ever hearing that you cannot connect both kinds to the same flue.

draft-fan-and-gravity-vent-p1027511.jpg

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  #2  
Old 1/3/08, 12:43 PM
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Default Re: Draft fan & gravity vent

Gravity vented appliances and induced-vent appliances can share the same flue system.



IF YOUR INSPECTOR IS NOT USING THERMAL IMAGING, YOU'RE NOT GETTING THE WHOLE PICTURE ®
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  #3  
Old 1/3/08, 12:53 PM
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Default Re: Draft fan & gravity vent

Shouldn't the smallest appliance (water heater) be "above" the others? This one seems to be "after" the others, but not "above" them. I'm not arguing the point, because I don't know, but it does look like the furnaces could push their exhaust down to the water heater.



Mark Nahrgang
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Home Inspections for Springfield, Dayton, and surrounding OH areas.
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Old 1/3/08, 1:04 PM
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Default Re: Draft fan & gravity vent

As long as the appropriate fittings are used, and the vents are sized and sloped properly, there's not an issue.



IF YOUR INSPECTOR IS NOT USING THERMAL IMAGING, YOU'RE NOT GETTING THE WHOLE PICTURE ®
Jeff Pope
JPI Home Inspection Service
Santa Clarita CA
(661) 212-0738
Santa Clarita Home Inspection
http://www.MyInspector.net


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Old 1/3/08, 1:28 PM
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Default Re: Draft fan & gravity vent

Jeff,
Do you know what the proper slope should be? I don't recall.
M.



Mark Nahrgang
www.DaytonSpringfieldHomeInspector.com
www.HeyMark.info

Home Inspections for Springfield, Dayton, and surrounding OH areas.
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  #6  
Old 1/3/08, 2:46 PM
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Default Re: Draft fan & gravity vent

1/4 inch per foot minimum rise. . .



IF YOUR INSPECTOR IS NOT USING THERMAL IMAGING, YOU'RE NOT GETTING THE WHOLE PICTURE ®
Jeff Pope
JPI Home Inspection Service
Santa Clarita CA
(661) 212-0738
Santa Clarita Home Inspection
http://www.MyInspector.net


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  #7  
Old 1/4/08, 12:41 PM
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Default Re: Draft fan & gravity vent

Did you check for back drafting?

The flue pipe must be the diameter of the largest appliance plus 50% of the other attached appliances.

I don't like the looks of galvanized gas pipe or the extension cord power supplies to the furnaces that are not protected. Or the number of unsupported fittings in the flue configuration.
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Old 1/4/08, 8:19 PM
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Default Re: Draft fan & gravity vent

Every one of the furnaces also had flexible hose through the enclosure too.

I did check for any obvious back drafting at the water heater when at least two of the furnaces were running.

Thanks for the replies.
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