mid-level efficiency?

It had a sealed combustion chamber but a metal vent. Is this an acceptable installation? I called clearance to combustibles.

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It may be OK Kenton.

See page 6

http://www.slantfin.com/documents/305.pdf (PDF)

Too freaky for me with that manifold contraption.
They just love tempting fate that it will not leak into the air intake.
Reminds me of those concentric vents.

Anyway the first thing I noticed was the slope on the exhaust.
Does not look like 1/4" per foot to me.

I don’t like the negative slope of the combustion air intake nor the foil type dryer’s vent pipe.

It looks like they have the connections reversed according to the pdf drawings that Michael provided. The exhaust should be in the center not the outside.

I think you are right. Direct vent type usually sends the exhaust through the center and combustion air in the outer ring.

Most of the concentric direct vent exhausts, I believe, are zero clearance and UL listed. That’s a lot of stainless steel vent pipe they have there $$$.

The exhaust does go through the middle.
It is the schedule 40.

Also… there’s plastic pipe meeting that manifold fairly close to where the metal exhaust vent meets it. It looks like heat transfer might melt the PVC.
This vent terminated within a foot of an operable window, which says to me that the installer was not qualified or didn’t care about proper installation.

Thanks Mike, that diagram makes it appear to be a sort of HRV, which seems like a good idea, but I’m not sure about the PVC, plus, to act as an HRV, the vent pipe would have needed to make a 90-degree turn just inside the manifold.

Too much guesswork here. Time for a specialist evaluation.


Looks that way to me too.

That doesn’t make any sense to me, Bob. Why install a PVC exhaust and a metal intake?

They wouldn’t spend all that money for a 3 inch stainless steel “intake” vent. The condensation tap and drain line is another clue that the stainless pipe is the exhaust vent. This boiler does specify stainless steel for the exhaust (I guess gas temps are still too high for PVC on this unit). PVC is specified as OK for the intake. They have definitely made the connection to the concentric terminal inside/out on this. Also should be minimum of 4 feet from the window.

If it needs a metal exhaust ,then it makes no sense to use a PVC air intake either.
The exhaust must get awfully hot if it must be metal.
Why would you surround plastic with hot metal and poisonous gas.?

Good catch. Sometimes you just have to be there. :wink:

Natgas has been in our area for only 8-10 years with not much showing up in inspections. Have not yet seen a concentric terminal for gas but have seen many for oil boilers/furnaces. They have been in use for 10-12 years and are known as sealed combustion / direct vent systems. They work well if properly located and installed. There’s a list of 12 “shall nots” for the vent outlet. Here’s a few:

A vent shall not terminate:

- under a veranda, deck or porch

- less than 3 ft from an inside corner of an L-shaped structure

- within 6 ft of an operable window, door, or mechanical air supply to any building including soffit openings

- within 6 ft of any combustion air inlet, unless the appliance is otherwise certified

BTW, the direct vent condensing units are considered “high efficiency”.

Because the manufacturer of the UL listed device said it needs a stainless steel vent and specifically not to use plastic for the vent. It was stated pretty clearly in the installation guide.

Properly installed, the intake air will pass through the outer ring of the concentric, not through the center - this one is configured inside out.