Thread: Gas Furnace combustion air intake

This 90+ gas furnace is using combustion air from the garage and is located near the water heater flue pipe. My concern is the potential for the air intake to draw in flue gases from water heater.

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Originally Posted by Trent Tarter

This 90+ gas furnace is using combustion air from the garage and is located near the water heater flue pipe. My concern is the potential for the air intake to draw in flue gases from water heater.

And if that did happen what would be the problem?

The Cat IV furnace intake is for combustion air and not for air that will be introduced into the living space of the home.

Thanks Scott, I just don't see it done like this very often.

That's not a proper way to support the thermal expansion tank, but I'm sure you wrote that up already.

If the furnace is pulling in combustion gases from the water heater then I'd be looking at the W.H. for drafting concerns. Also, combustion gases are very corrosive and wreak havoc on heat exchangers.

I would check that combustion air to garage space is OK for combined BTU's of furnace and H2O heater. By volume it would require a rather large garage to meet the combustion air requirement.