Thread: May PVC vent route downwards?

Is the PVC exhaust vent for a high efficiency gas furnace allowed to run downhill? The one I inspected today has 3 elbows and about 2' downward pitch in around 10' of run. Is this allowable?
Thanks for any replies.

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Only if you mean downhill toward the unit (which you do not).

That running trap on the condensate line is not allowed either.

Does that vent go down and into the clothes washer standpipe or vent stack? Sure looks like it might.

No, that is the rear wall of the house; it discharges through the wall to air. So at least the condensate is outside at that point. What I was worried about was the induced draft fan having to push against that downslope, especially after those 3 elbows.

Is that exhaust? I think it is air intake.

Patrick

Good question! Looks like a combustion air supply. Most (all I can remember at this time) exhaust lines I've seen are 3" PVC.

It is definitely exhaust; it is the discharge from the induced draft fan. The intake is simply a PVC grate sort of plug on the opposite side; it is using room air for combustion. (This is in a tuck-under garage, along with the laundry as someone noted above.) I am noting it as a questionable installation which needs to be blessed by someone with a mechanical license. And while I realize the fan forces the draft through the furnace and that this is much cooler than a typical mid-efficiency unit, my concern is that the extra power that will be required to force that warm air back downwards would slow the overall flow through the heat exchanger.

Originally Posted by Linda Swearingen

No, that is the rear wall of the house; it discharges through the wall to air. So at least the condensate is outside at that point. What I was worried about was the induced draft fan having to push against that downslope, especially after those 3 elbows.

Linda, no problem with the " induced draft fan having to push against that downslope".

The problem with sloping toward the outlet is the condensate. In cold weather, the condensate will freeze, causing a giant icicle at the exhaust termination. This icicle will continue to grow, and will eventually cause blockage at the outlet, causing the furnace to shut down and produce no heat when the occupants need it most. The colder the weather, the farther back in the pipe the water starts to freeze.

Generally (I say this because there's always some exception out there), the vent should slope all the way back to the unit, causing the condensate to drain back to the unit and through its condensate management system.

Assuming it is the exhaust of a cat 4 furnace it is wrong however as someone commented before, it does look to be in the position where I see the air intake more often.
The exhaust and air intake should both be run to the outside.

You want the same atmospheric pressure for both and do not wish to create a negative pressure inside the utility area where it has potential to cause back drafting of the Water heater unit for instance.
Another concern I see is the laundry facilities as chemicals such as bleach can compromise the HVAC equipment and cause performance /safety issues.
I recommend you have a HVAC tech come in and examine this situation.
See my graphics taken from a Rheem cat 4 furnace install manual.