How to slope air intake tube on sidewall venting job??

alanmuller · June 11

It's usually given clearly that the exhaust should be sloped back to the appliance. I've done the same with intakes. But recently I encountered a job where a good bit of intake tube condensate was running into the furnace where it clearly did not belong—soaking the gas valve and wetting down wiring. The intake runs through about 4 feet of cool basement and

I'm thinking that warm humid outside air is getting drawn in via the house ventilation fans. This system has been in place for over ten years without this problem being observed before.

I could rework the intake tube to slope away from the furnace but should this be necessary? seems to me it should not be unless there is a defective heat exchanger.

Any advice?

pecmsg · June 11

how are you drawing in air in a sealed system?

If the heater is not running no air should be moving between the intake and exhaust.

Is the heat exchanger compromised?

JUGHNE · June 11

I usually put a wye clean out in the horizontal pipe near the furnace.

The plug points towards the furnace and down. Then drill a couple of 1/4" holes in the plug. Any moisture flowing toward the furnace will collect there in the angle of the wye and drip out as an indicator.

Also this plug is only finger tight and can be removed temporally to allow inside air for combustion if the inlet is closed up for any reason. Also to test the inlet pipe for blockage.

Mad Dog_2 · 1:06PM

Every manufacturer could have different requirements, but I prefer to keep air intakes pitched away from unit to keep the water from a down pour and even snow away from the unit. Mad Dog

How to slope air intake tube on sidewall venting job??

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