Thread: Direct Vent Flue

This is a Bryant (or BDP) Plus 90 furnace, direct vented through the roof. The roof termination did not look right to me at all. I cannot find an actual installation manual from Bryant on line, and there was nothing at the house.

The vent was two 2" PVC pipes joined into a 4" PVC pipe. The back of the furnace was blocked from view by some fiberglass insulation, so I couldn't see the transition coupling. Does anyone have a photo of a correct furnace flue cap for a direct vent Cat IV furnace?

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Jim,

I would say it is not correct based on at least three/four things:
- there is no way that open space would be allowed to face vertically to rain as it would be direct tremendous amount of water back into the furnace (having just gone through 3 days of about 15" of rain, that would be full of 15" of water if that had been here)
- that is a Type B Gas Vent cap and Type B Gas Vent is not allowed to be used with positive pressure systems
- that looks to be Type B Gas Vent inside the outer sleeve and Type B Gas Vent is not allowed to be used with pressure systems
- as I recall the vents for those furnaces are plastic to resist the corrosion build up and that is metal

I am sure that there are many more things wrong with it which people with more knowledge of those types of furnaces will point out.

Also, that is that 4-sided top for, hopefully not for another gas appliance and hopefully not for a clothes dryer - those are not really much good for anything.

I think this is what your looking for.

I see several problems with that installation.
Carrier/Bryant allows for the concentric vent kit shown in the attachment. Notice, the inner vent pipe in the allowed concentric vent is one piece. This eliminates the risk of pulling exhaust gas back into the combustion air, unless the pipe is physically broken. The picture of the installation shows several seams; any of which could leak and allow vent gas to be pulled back into the combustion air
A cap on the vent ( I hope that the inner pipe is the vent). This will contribute to condensation collecting around the outlet and freezing. This freezing will cause nuisance pressure switch trips, and lock-outs of the furnace. No heat, at the time it's coldest outside.
I would be very interested to see how the two pipes were brought together using B-vent. I know of no "pre-made" coupler designed to acheive this. This type of coupler would defeat the initial purpose of of the B-vent.

Originally Posted by Jerry Shipman

I think this is what your looking for.

Jerry S.,

I see a problem in that drawing (a few, but this one specifically):

The drawing shows the "vent" out the top, the "combustion air" into the bottom, then states "Maintain 12 in. (18 in. for Canada) above highest anticipated snow level. Maximum of 24 in. above roof."

Is that is saying that there is only 6" of snow on a roof in Canada?

Or that *if there is more than 6" anticipated snow level* *do not use* - which would mean there are many areas of this country and Canada, where that could not be used.

Heck, where we lived when I was a kid, 40 miles south of Buffalo, NY, we had more snow on the roof than that.

Then there is the "vent" discharging vertically up and open to the rain ... and snow? Just seems like a dumb idea to me.

I've found videos and all sorts of install instructions but just where is the rain going in these things? Sorry for the silly question

The drawing is directly from the Carrier/Bryant installation manual.
Yes, if anticipated snowfall would require the vent to be more than 24 inches from the roof to the bottom of the rain cap, it should not be used for a roof termination. It can still be used for a sidewall termination.
The open vent is not an issue, as a condensing furnace is designed to drain water back to the furnace, and out through the drain. Condensation from the running furnace will actually produce and return more water back through the furnace than a heavy rain would.
Also, looking at the original installation and the gravel roof, is this a residential dwelling, or commercial? If it's not a home, why are they using a residential furnace in a commercial application?

Originally Posted by Jerry Shipman

The open vent is not an issue, as a condensing furnace is designed to drain water back to the furnace, and out through the drain. Condensation from the running furnace will actually produce and return more water back through the furnace than a heavy rain would.

You are, of course, referring to normal conditions.

I am questioning that aspect based on above normal conditions because "normal conditions" only represent 'the average', meaning that if 50 is normal, then you might vary from 0 to 100, which is quite a bit of variance to allow for.

I can see snow clogging that vent during blizzards, at least like some I remember seeing and being in.

Currently, right next to us in parts of Daytona Beach, they have had 24" of rain in 5 days (as of last night) and here in Ormond Beach we have had 17" of rain in that same time, with another 4" expected today and tomorrow. I am glad we live in a higher area on a ridge of sand, the road and yard floods, the rain lets up for a few hours, and the water drains down to dry street again, then floods again as the rain comes back. Other areas not far from here are flooded with 2 feet of water in the houses. This is the most rain on record for this area not associated with a tropical storm, and maybe the most on record even when associated with a tropical storm - the news last night said they are going back and reviewing the records to find out.

I suspect this much rain would not be handled well by that vertically facing vent. Just my opinion.

Although not likely, I would say that it is possible a heavy blizzard could clog the vent. Remember, the vent gas is much warmer than the snow, causing it to melt faster than it could collect.
As far as rain, a properly drained furnace can easily handle and dispose of several gallons of condensation per hour. You won't get near that amount of water in a two or three inch vent pipe.

What total scumbags. To me it looks like they tried to make their own concentric fitting. Write-up it as D&H and make their life hell.

Brian that goofy looking sleeve as an air intake is what they are speaking about

Maybe it is just a sleeve, still wrong but a sleeve. Who would run PVC then change to metal? You did say you could not see the transition. Maybe the PVC was plumbed out elsewhere ?

I questioned whether a B vent was in use on a job last week, but could not locate any other termination. I pulled the rain cap only to find that it was capped off inside (they were using the fireplace flue--oops).

You may be able to pull the rain cap and peek down the flue.

Meanwhile, today I'm pondering this arrangement: Cat I furnace vented in single-wall, had to stick my camera up at arms length along the side of the utility closet and aim where I though it should be entering the wall...