Thread: Direct Vent Furnace Venting Downhill

I have never seen a direct vent furnace venting downhill like this. I reviewed the Ruud Installation Manual and didn't find where they specifically ruled this out, but in reviewing a few other direct vent appliance manuals, I saw wording such as "vent piping cannot under any circumstances be run downhill".
And oh yes..this is installed in a bedroom closet with louvered doors right next to a CAT 1 water heater and as vented the furnace is not obtaining all combustion air from the exterior.
Does anyone know if a downhill vent run like this is ever acceptable?

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Nothing?

Horizontally -o.k. - Upwards - o.k. - but downwards?

Is this something you pros see all the time?

No opinions?

Originally Posted by David Tontarski

I have never seen a direct vent furnace venting downhill like this. I reviewed the Ruud Installation Manual and didn't find where they specifically ruled this out, but in reviewing a few other direct vent appliance manuals, I saw wording such as "vent piping cannot under any circumstances be run downhill".
And oh yes..this is installed in a bedroom closet with louvered doors right next to a CAT 1 water heater and as vented the furnace is not obtaining all combustion air from the exterior.
Does anyone know if a downhill vent run like this is ever acceptable?

The Rudd manual will be the one to go with.

Thinking about it logically, the exhaust air/gas is being forced out by a fan so it does not depend on gravity. So logically it should not be an issue. But...... then we have to deal with the condensation that is a major byproduct of a CAT IV furnace. With the flue going downhill or a negative slope how will the condensation be disposed of? It won't be and it will collect in the lowest part of the flue and will eventually form a blockage or trap.

So, I would have to say that it is a bad idea and it is not allowed. If you want documentation to back up such a statement you might need to call Rudd and I bet the can email a document that says so.

Ruud was no help, but I was able to speak to someone at Rheem (Arkansas), and he verified that this was wrong and cited their 1/4" per ft. pitch upwards rule for all horizontal pipes as the documentation for citing this as disallowed.

And.....he requested photos of the install, and had already spoken to someone higher up in the organization about this.

Perhaps someday soon we might see the Ruud/Rheem install manuals call this out more clearly, as some other manufacturers of direct vent appliances are currently doing.

(kind of like McDonalds having to tell people their coffee is hot, but who knows it might actually prevent a mishap someday)

Thanks for you input Scott.

The water heater in bedroom is a code violation. Recomend fixing asap.

Simple "fix". Take the bed out of the bedroom.

rick

David, you did the right thing first by consulting the listed instructions then the mfr. directly. That covers if it is *acceptable* or not. Then you have the functional aspect. Here, you would be concerned with the condensate forming a trap and the additional elbows adding flow restriction. Another problem could come at the exterior wall. You have the potential for an ice blockage if this is draining towards the vent termination.
HTH,
Any more pics of that WH venting?

My biggest question is, if the water heater venting can go up, why couldn't the furnace venting? If the PVC has the proper drain tee installed at the bottom of the lowest point the system may run correctly but, every manufacturer I have delt with specifies a 1/4" pitch back to the unit.