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Cat 4 Termination for Direct Vent


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I looked at a Cat 4 furnace on a 3 story bldg. for a 2nd story condo. 10 yr old furnace and rehab. The exhaust was going out horizontally through an adjacent wall and the combustion supply was coming through the roof (I think). It was direct vent (2 pipe) so I cannot imagine why this was done.

The exhaust and supply are supposed to be near each other. Nothing bad seems to be happening. Would you make a big deal out of this or just say this isn't the way it's supposed to be?

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Just a WAG....

The installer dweebed out and mixed up the intake and exhaust. I've been seeing installs where they've finally gotten smart enough to take the exhaust out the roof, but to save a penny they put the intake out the side. When the furnace went in, the guy never checked the pipes to see which was which.

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The intake and exhaust don't have to be near each other, just in the same atmospheric zone. Outside would be the same zone.

No idea why the two pipes in two directions, though. Seems much more expensive. Sounds like the installer isn't up to speed on those furnaces. . . ?

The Tappan instructions say not closer than 18" no further than 36" for vent termination. I think. I'll have to double check.

Why atmospheric zone? Why wouldn't they just say "outside" or "within the mass of air that surrounds the earth"?

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I'll guess it has to do with balancing the venting process. I don't know whether to make a big deal out of this since I have not seen this before.

The colder the climate the farther the spacing should be but within limits.

The furnace in question is a Tappan FG6RC.

There are many things wrong with this installation. This was just one.

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I got this reply from an HVAC forum and it makes sense.

"The real world issues with terminating a high eff furnace flues in different pressure zones is that they will be subject to different airflow patterns. Wind on one sie and not the other will cause pressure switch waffling, nuisance board lock outs, and depending on how well they are run, water accumulation in the flue(s) which can cause the furnace to shut down and/or improperly burn. Another common issue with running them to different locations is that they will rarely be of equivalent lengths-presenting many of the previously mentioned problems"

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I got this reply from an HVAC forum and it makes sense.

and depending on how well they are run, water accumulation in the flue(s) which can cause the furnace to shut down and/or improperly burn.

I don't understand this part. It sounds more like an indictment of a poorly installed flue than a problem of running the flue and intake to different areas. Am I missing something?

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Sounds like the installer isn't up to speed on those furnaces. . . ?

Chicago is the land of confused HVAC installs. We look at a lot of joints that were originally steam or hydronic, that were converted to condos or apartments a while back when no one cared; tech's stuffed equipment in any old place it would fit, even kitchen pantries with the return located in the kitchen. Ducts hidden in cheesey soffits, lousy air flow, vents into ventilation shafts, all sorts of crap.

I'm betting this is one of those kind of places.

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