Direct Vent Pipe for B-Vent Fireplace?

[franticvike]

Hi,

New member and very much appreciate any insight.

I recently removed my brick chimney as part of a larger renovation. I've kept the frame of the hearth and am installing a zero clearance fireplace.

The fireplace I have is a Kingsman ZV3600N. It's a "Vented" or B-vent model with a 4" attachment point. Down the road I plan to replace it with a double sided or see through unit, which will be direct vent.

Ideally, I'd like to install the venting now that will be required for the direct vent model. My question is whether I can use (as is or modified) a direct vent duct/pipe system to vent the B-vent fireplace?

Based on the pure sizing of the parts it seems like it should be possible (the 4" b vent is the same size as the exhaust air vent on a 4" direct vent). Could I also install now a 5" direct vent and down size to attach to my 4" B-vent?

Thanks

 

[Tech Guru]

No, if an appliance is B Vented it need to be installed with B Vent (or a aluminum liner within a masonry or metal chimney - which effectively becomes B Vent by definition). Direct Vent pipe is not certified as B Vent, AFAIK no manufacturer does this - most will make a B Vent and a Direct Vent pipe as separate systems (I only use the term 'most' as some don't manufacture B Vent at all). You'd also have to potential for someone trying to install a Direct Vent sidewall termination on a system that requires natural draft/chimney action.

 

[franticvike]

Thanks Tech Guru. I've received the same answer from a few people, but I'm struggling to rationalize it. The "exhaust" portion of the direct vent conduit is doing the same job as the "B" Vent pipe, no? Is there a difference in exhaust temperature?

Anyway, my installer wouldn't play my crazy game, so I've had the proper "B" venting installed through the roof.

My question now is with the point where the "B" vent penetrates the roof. The underside of my attic is insulated with spray foam. He cut everything back at least an inch, but it's a fairly large opening that he created for the boot. Can I fill that opening with rock wool insulation or the like?

 

[Tech Guru]

Sorry, been a few days since I've been online here. Just to get it straight, it sounds like your are detailing that the installer has cut the spray foam insulation back 1" around the B Vent pipe where it penetrates the roof. That is the correct thing to do. Officially that area should be left as air space around the B Vent pipe, which requires a 1" clearance unless otherwise specified by the fireplace manufacturer. It would not be wise to fill that space with anything, however, if you do, make sure it is a non combustible insulation.

 

[franticvike]

Got it, thanks Tech.