Draft fan & gravity vent

[Ralph Brady]

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.

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Thanks

[Jeffrey R. Pope]

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

[Mark Nahrgang]

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.

[Jeffrey R. Pope]

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

[Mark Nahrgang]

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

[Jeffrey R. Pope]

1/4 inch per foot minimum rise. . .

[David A. Andersen]

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.

[Ralph Brady]

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.