Thread: Power Vent utilizing "B" Vent

Ran into this one yesterday. Lennox boiler with a power vent. Single wall vent pipe connected to the power vent, transitions to a "B" vent, runs horizontally approximately 16 feet between the floor joists and exits the exterior wall.

I called it out for clearance to combustibles and improper venting material, but I've never seen a set up like this before. What do you think?

Similar Threads:

• Vent Tee
• Crawlspace vent fan
• Kitchen vent
• That dread Exhaust Vent - Texas gang
• Roof Jack w/ Neoprene Boot At B Vent

You probably know this, but induced draft is still Category 1 and a B-vent is required. The label on the boiler should specify. Clearances to the gas vent pipe are wrong as is the termination at the exterior (assuming Cat.1). If a forced vent, then the B-vent is wrong. Best to defer.

Label on the boiler said to install the vent in accordance with the installation manual
Of course the manual wasn't there. To me the vent appeared to be a power vent, not an inducer, but I could be wrong. The single wall pipe was pretty hot. I figured the B vent was incorrect, most likely should have been a special vent, sealed stainless steel with proper clearance, but couldn't be positive without the manual.

The single wall vent connector clearance is 6" and the B-Vent clearance to combustibles is 1" the B-Vent should have terminated through a wall thimble and an exterior termination kit. I can't see when the B-Vent started but assume it is between the floor joist at some point. You are correct that the clearances are wrong and it needs to be corrected by an HVAC professional.

Originally Posted by Dan Hagman

I can't see when the B-Vent started but assume it is between the floor joist at some point.

Between the floor joist in the second picture, just past the elbow.

Originally Posted by Ken Rowe

Ran into this one yesterday. Lennox boiler with a [color=red]power vent[/color=red]. [color=red]Single wall vent pipe connected to the power vent[/color=red], transitions [color=red]to a "B" vent[/color=red], runs horizontally approximately 16 feet between the floor joists [color=red]and exits the exterior wall[/color=red].

I called it out for clearance to combustibles and improper venting material, but I've never seen a set up like this before. What do you think?

If the vent is under positive pressure then the venting must be listed to UL 1738. It is a problem as unlisted venting (single wall connector, for example) is not approved for positive vent pressure. You can use an 'inducer' that gets draft going but the draft does become negative as it warms up still requires vertical venting.

Power vents must have a draft proving switch and must be interlocked to the gas control.

Sidewall venting must be under positive pressure. If it measures negative vent pressure then it must vent vertically.

Perhaps if the "power vent" were installed OUTSIDE but you'd still hve rise vs. run problem indoors and require interlocking & proving switch.

If neg pressure can not vent through side wall. Rise vs. run problem, and failure to maintain minimum overall rise from the appliance, in addiiton to what was already mentioned. "B-Vent(ing)" system instructions defer to NFPA 54, NFGC, or by its ANSI designation. Failure to overcome snow ground cover depths for the region, failure to elevate above vertical wall at termintion when within required clearnces, esp. at grade, occupied surfaces such as walkways, decks, patios, and roofs, etc. 1 or 2" within 8' verticl for less than 12" b-vent for flat ares, for MN, IIRC. No proper termination, sidewall open horizontal termination not allowed (no open ended vent period. No protection from prevailing winds reverse draft & blow-out.

That appears to be an induction fan to me. I think only high efficiency Lennox boilers have a power vent and that doesn't appear to be one of their high efficiency units, but I don't see a lot of boilers around here.

The B pipe in a power venting situation draws in cool air through the outer pipe to cool the
heated gases when burner is operating. I see the problem here of vent gases maybe being sucked back into the return venting outer shell. I wonder if past residents had headaches?

Hi Ken;

Sidewall venting of a fan assisted appliance is not common, but sometimes acceptable. I'm not saying the B vent is acceptable, but sidewall venting sometimes is.
In my area, I run across this set-up once or twice a year.

Sorry for the one blurry photo!

Originally Posted by james hiatt

The B pipe in a power venting situation draws in cool air through the outer pipe to cool the
heated gases when burner is operating. I see the problem here of vent gases maybe being sucked back into the return venting outer shell. I wonder if past residents had headaches?

No it doesn't, and its not "B pipe" its "B-Vent".

Probably not the exact unit:
http://www.lennox.com/pdfs/installat...WB8-IE_IOM.pdf
Looks like the install is half right, based on a quick read, page 13 covers "optional horizontal venting with power venter" with single wall and B-vent pipe, and the need for sealing the joints and p. 10 calls for the wall thimble. Some of the installation will be based on the Power Venter used.

Originally Posted by Mike Kleisch

Probably not the exact unit:
http://www.lennox.com/pdfs/installat...WB8-IE_IOM.pdf
Looks like the install is half right, based on a quick read, page 13 covers "optional horizontal venting with power venter" with single wall and B-vent pipe, and the need for sealing the joints and p. 10 calls for the wall thimble. Some of the installation will be based on the Power Venter used.

I disagree, its (what the OP pictures and describes) 100 percent wrong. It is a Cat I boiler improperly vented as Ken Rowe pictured and described. There is NO power vent, baro damp, or interlock to same present as pictured, thats an inducer. No rise, SW connector and offsets clearance violations, Type B Gas Vent improperly installed and improperly terminated.

No provisions to protect boiler from the forming condensate, which WILL form in such a set up in Minnesota installed like this (basement boiler improperly sidewall vented, barely above grade, insuficient rise, lacking power vent, completely improperly terminated, through the bsement wall just above the cold sill plate, from forming, especially after a good snow fall or two and the wind is blowing, even if it is on the south or east side, or south-east side of the house.






Boiler is and as an orphan and should be b vent or special gas vent all the way from inducer fan outlet or the SW increaser from the inuducer fan outlet to a correctly installed as per NFPA 54 and vent mfg. instructions, or IF using side wall venting, sealed b-vent from same or special gas vent to a power vent which goes outside and requires interlock and baro dmp.

That wall/fence alcove and failure to terminate correctly makes for prime blow-back, esp. during the heating season (when the snow is really piling up) in Minnesota.

The OP said power vent and a Lennox unit. I just did a quick google of Lennox Boiler with a power vent and found these instructions. Based on a "QUICK" read simply said it looked half right and mentioned a couple items that looked wrong. These instructions covered basic inducer and power venter connections, with additional instructions based on the power venter used. Yes, there are issues, but I could not say if it is 100% right or wrong based on the one photo and not knowing what unit is installed.

You can clearly see the inducer fan, it is a Cat I, and as pictured and described is 100% wrong, single wall unlisted galvanized vent connector within 6" of sill plate is always 100% wrong, this isn't a dryer duct (as CLAIMED by Ken Rowe, the OP!). Therefore yep 100% wrong in the unpitched horizontal vent connection, SW elbows/offsets to (as claimed by the OP) Type B Gas Vent through the wall horizontal and without termination period.

Single walled vent connector and B-vent are NOT approved for positive vent pressure-period! This does appear to be an induced draft CAT I appliance, which means vertical venting. Regardless, B-vent can NEVER terminate horizontally like that and yes, clear fire hard and no listed termination. Some appliances are approved for use with a horizontal wall power vent that sucks the fumes out but never blow it out with B-vent or single walled.

Its fan induced negative pressure vent boiler. With side wall venting, it needs power vent mounted on the wall (something like this Field Controls Product Gallery : Combustion Air : Combovent_Angle ) and single wall between (it will be negative pressure). Also power vent needs to be 12" over anticipated snow level.

Originally Posted by Zibby Bujno

Its fan induced negative pressure vent boiler. With side wall venting, it needs power vent mounted on the wall (something like this Field Controls Product Gallery : Combustion Air : Combovent_Angle ) and single wall between (it will be negative pressure). Also power vent needs to be 12" over anticipated snow level.

Its parallel and too close to uninsulated outside wall plate, sill plate and rim,above grade block basement and does not share with any other appliance. It should be (IF power vent installed to SUCK it out at outside wall) b-vent or special vent all the way from the inducer outlet to outdoors. Without a power vent at the end, it MUST be vertically vented and terminated above the roof.

I'm a little late to the party on this one, but am digging into the allowable uses for a power vent or added in-line draft inducer, vent materials allowed, etc.


What are your thoughts regarding this companies product recommendation for single wall vent? http://www.tjernlund.com/Tjernlund_8504003.pdf

As far as sidewall venting, it looks like this same company recommends single wall vent pipe:
http://www.tjernlund.com/Tjernlund_S...it_8500594.pdf

So far, the only vent type I've found that is rated for Cat 1,2,3&4 venting is the Selkirk Saf-T vent: Selkirk: Saf-T Vent EZ Seal


ADDED: Under their FAQ section, they indicate that their in-line draft inducer is allowed to be used with B vent. I've contacted Selkirk and Dura-Vent to get their take. (did so earlier today)