Question about B-vent termination and CO
We have a three story duplex right outside Philadelphia thats heated by a gas boiler and convectors. Separate gas water heater and gas boiler (Williamson GWA 140N-S, 140K BTU) exhaust into the same flue in the basement laundry room, which is run outside through the basement wall and up the back of the house through 6” B-vent before terminating roughly 6 feet from the third floor bedroom window. The bedroom window in question is in a shed dormer on the back of the house.
I’ve attached a photo of the vent running up the exterior wall, and a link to a video from the 3rd floor bedroom window showing the vent in action.
I’ve never liked this setup as I suspect the system is exhausting too close to the window and/or not high enough above the shed dormer roof/main roof ridge. Depending on the wind, exhaust gets blown against the window and/or the shed dormer. I occasionally get low level CO readings up in that room using a low-level detector. I’ve taken readings in the boiler room and no CO is detected.
This setup, while ugly and probably not ideal for other reasons, is very common in this area, as when these homes were built in the 20s and 30s they all featured central plant steam heat piped into the house directly. They were all laid out to reflect that they supposedly would never need boilers or furnaces. Thus the chimney is on the other end of the basement from the laundry room where the boiler is located. These homes all had to be retrofitted with exterior metal flues in the 70s when the steam plant company abandoned operations.
What can we do about this? Extend the b-vent higher with roof brackets? Power venting?
Thanks in advance.
Comments
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First of all, that B-vent does not meet code requirements. it is obvious that there was no municipal permit issued for this install, or the local inspector is clueless.
Secong big No No is that B vent should not be exposed to the outdoor temperature for the entire vertical distance. And there are several other things that are wrong. I will make a diagram of what might be a better design.
BRB
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Yeah, my understanding from talking with local building and code people is that when the old steam plant abruptly ended operations in the early 70s suddenly tens of thousands of people in this area were without heat and the local utility company and the state utility commission had to scramble. So they slapped these things up fast and they’ve basically been grandfathered in/ignored even though no one likes them.
Anyway, thank you very much for your time and feedback. Let me know if I can provide any additional information, photos, etc.
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Here is the lowest cost fix
Here is an instruction guide for one manufacturer of B-vent. all the others are about the same. The diagram on page 5 figure 11 shows you basically what I have drawn for you. H&C B-Vent. the reason this has worked for so many years is the higher exhaust of a steam boiler, But when you get extreme cold or if the wind is in a certain direction, you can have down drafts that can put Carbon Monoxide inside your home, even if the windows are closed. The top of the vent MUST be at least 2 ft above any obstruction within 10 feet. The peak of your roof might be too close so you need to at least 2 ft higher than that. Just that pipe may not have enough support above the roof line to get a pipe up that high so the enclosure should be affixed to the building in such a way that it will support that long vent pipe above the roof line.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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I appreciate you taking the time to diagram that out. You’re proposing we build another chimney — albeit an insulated one — on the back of the house, basically, which makes sense.
I’m visualizing how that might be done. Unfortunately the house has shallow eaves; the overhang is shallower than the 6” B-vent is wide, so running the whole thing through the roof isn’t feasible. Seems like we’d have to bump the new “chimney” out to clear the gutters entirely and make it tall enough to terminate above the main roof ridge.
Ugh.
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Same vent pipe with a plywood enclosure (like T111 siding) that has 1.5" foam sheathing glued inside it to form an insulated enclosure for the B-vent. A decent carpenter can notch out the eaves so that you do not need to have so many 90° turns. Then make a chimney covering out of plywood to support and insulate some of the B vent above the roof line until you get high enough to top the B vent chimney above the peak of your roof.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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building a chase and sealing it to a brick building will be a bit of a task
A power vent out the side might be an option if you can get clearances from openings and windows
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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Yeah and the dryer vent would have to be moved since it’s literally right next to the b-vent. Also since it’s a duplex we share a common gutter with our neighbors so I’ve have to get my gutter guy out to see how he’d handle it.
All told it’s not like building the pyramids or anything but if there’s a simpler solution I’m all ears even if it costs a little more.
What are the required window and door clearances to power vent out the side?
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Probably better to ditch the boiler and put in a MOD CON
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FYI, here's a previous discussion of required clearances for power venting. You'd have to confirm with the experts for your situation, but in this case the required clearance was 4 feet from operable windows. They were using a large capacity vent because they had multiple boilers and water heater(s). Your requirements may be more modest.
They used a Field Controls SWG-8 based on their large BTU requirement. You would probably be able to use something smaller like an SWG-4.
https://www.supplyhouse.com/Field-Controls-SWG-4HD-4-Power-Venter-170000-BTU
The installation instructions for the entire line of Field Controls SWG power vents say a minimum of 4' clearance to windows above or to the side. So that glass block window to the side may be your problem. If you could locate the vent "above" that block window, then you only need 1 foot clearance to windows "below."
So if you could get 1' above that block window and stay 4' below the other window above, you might be good. Worst case, you might need to knock out that glass block window and brick it over.
I am not a heating pro, just a homeowner/engineer, so you should confirm everything with a heating pro here.
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If it is solid glass block and is not an operable window it shouldn't be an issue.
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I thought this was steam based on what @FrankMaraschino said: "Yeah, my understanding from talking with local building and code people is that when the old steam plant abruptly ended operations in the early 70s suddenly tens of thousands of people in this area were without heat and the local utility company and the state utility commission had to scramble. So they slapped these things up fast and they’ve basically been grandfathered in/ignored even though no one likes them."
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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There are two different charts on the clearance form open windows and doors and air intake openings. One is for direct vent when you have the combustion air drawn from outside and the exhaust gas both from the same pressure zone of the building. This is not the case for you.
The second diagram is when you have a power vent situation where the combustion air is drawn from within the building and you have a fan the forces the exhaust out of the building. Like an SWG-4
Here is one example of that diagram
this information comes from Field Controls Venting manual It appears that the basement glass block window with the center vent opening will need to be permanently closed. The best way is to have 2 more glass blocks installed where that vent is located.
the photo on the right would be acceptable as a permanent closure.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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my understanding of the code is
IF the window can be opened meaning NOT putting a screw in to say it can’t then it’s NOT allowed!
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A direct vent appliance is the best option as it reduces the required clearances down to one foot from four feet that would be required with a power vent . it will also take care of any combustion air required as the second pipe is bring outside air into the appliance for combustion
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