Thread: B-Vent Installed Horizontally Outside House

The installation was a 2 year old 80% efficiency gas boiler with an aftermarket sidewall vent assist fan up at ceiling level in the basement. The B-vent was routed to the exterior through the poured concrete foundation wall, beneath the rear exterior deck, and the total exterior length of the flue pipe run beneath the deck was about 10-12' with a 90 degree elbow in the run. It had inadequate clearance beneath some of the deck framing and condensate staining was showing up on a couple sections of the flue pipe beneath the deck which is not a surprise.

I'm fairly certain this horizontal installation and routing through the foundation wall with no thimble is wrong but wanted to make sure as I couldn't find any references that specifically state the flue pipe cannot be installed horizontally. I did read in a previous thread that Metal-Fab does allow for exterior installation.

Thoughts?

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Originally Posted by Nick Ostrowski

The installation was a 2 year old 80% efficiency gas boiler with an aftermarket sidewall vent assist fan up at ceiling level in the basement. The B-vent was routed to the exterior through the poured concrete foundation wall, beneath the rear exterior deck, and the total exterior length of the flue pipe run beneath the deck was about 10-12' with a 90 degree elbow in the run. It had inadequate clearance beneath some of the deck framing and condensate staining was showing up on a couple sections of the flue pipe beneath the deck which is not a surprise.

I'm fairly certain this horizontal installation and routing through the foundation wall with no thimble is wrong but wanted to make sure as I couldn't find any references that specifically state the flue pipe cannot be installed horizontally. I did read in a previous thread that Metal-Fab does allow for exterior installation.

Thoughts?

Can't read the UL listing info on the pic/label (too blurry).

Everything (limited ability to see what's in photos) seen & described looks and reads as wrong in selection, application, and execution.

Metal-Fab Model O 3-6" B-Vent Installation UL Listing MH7860 Instructions (can't read label info at this end):

GENERAL:
The Model M and MO Gas Vents (B-Vent) have been designed for use with gas burning Category 1 appliances. A Category 1 appliance operates with a non-positive vent static pressure and with vent temperature that avoids excessive condensate production in the vent.

SAFETY:
CAUTION: UL listing is based on using B-Vent components supplied by Metal-Fab, Inc. Performance may be affected and a safety hazard created if parts shown in these instructions are not used.

1. Metal-Fab B-Vent pipe and fittings were designed and are listed to form a continuous passageway from the gas burning appliance to the vent termination ABOVE THE ROOF, including the vent cap.

5. For horizontal runs, maintain a pitch or rise from the appliance. Minimum rise is 1/4 inch per foot.

6. ...For installations not covered by the above, ...the lowest discharge opening of the vent cap should be at least 2' above the highest point where it passes through the roof, and at least 2' higher than any portion of a building within 10' horizontlly....

7. Vent sizing is DEFINED BY TABLES IN NFPA 54 (ANSI Z223-1, 1999), or contact your Metal-Fab supplier. Install in accordance with these instructions and local code requirements.

10. When installing exterior vent, not enclossed by the structure or chase, consult locl gas utility, applince mnufacturer, and/or authority having jurisdiction.

11. If power vent fan is used, make sure it is located at the terminus (exhaust end) of vent system, so as to maintain negative pressure within the vent.

Thanks for the info HG.

How about vent slope? Was that maintained? Galvanized steel through concrete will get eaten up.

Pipe had zero slope. I noted that in the report as well as the pipe being encased in the concrete foundation wall, condensate staining, in contact with deck framing, etc.

How many times do we wonder if the installer was stupid, ignorant, or just didn't give a dang as long as he or she got a paycheck?

It's funny because as I was looking at this, 1/2 of me is saying to state it's all wrong but the other 1/2 is saying to hold back just in case the manufacturer has some provision allowing it. It was so out of the norm I figured I had to give it a chance to possibly be correct.

Nope.

Originally Posted by Nick Ostrowski

The installation was a 2 year old 80% efficiency gas boiler with an aftermarket sidewall vent assist fan up at ceiling level in the basement. The B-vent was routed to the exterior through the poured concrete foundation wall, beneath the rear exterior deck, and the total exterior length of the flue pipe run beneath the deck was about 10-12' with a 90 degree elbow in the run. It had inadequate clearance beneath some of the deck framing and condensate staining was showing up on a couple sections of the flue pipe beneath the deck which is not a surprise.

I'm fairly certain this horizontal installation and routing through the foundation wall with no thimble is wrong but wanted to make sure as I couldn't find any references that specifically state the flue pipe cannot be installed horizontally. I did read in a previous thread that Metal-Fab does allow for exterior installation.

Thoughts?

This is also wrong because it appears the horizontal run is longer than the vertical. There is definitely a need for a thimble of some kind as it passes through that masonry.

Ashley Eldridge
CSIA Director of Education
Chimney Safety Institute of America (CSIA) | Plainfield, IN