Connect B vent stove to class A chimney

[nmr]

I have an existing stove I don't think is installed correctly. It's a Regency U38 vented with 4" single wall pipe to a Metalbestsos SS 8" chimney. The stove is a 4" B vent stove.

I want to fix it so that it can be moved closer to the wall, and have it be 100% by the book.

Can it even be done while still following the manufacturer's instructions? Biggest problem I see is I can't find a listed way to go from the chimney to B vent. The Selkirk chimney pipe are all listed for DSP, AFAIU B vent won't connect.



These are the stove venting instructions:

A four inch diameter vent is required. B-Vent, Class A or Masonry with an approved liner are all acceptable

 

[nmr]

Called Regency today, Barjit told me that single wall pipe is acceptable with the U38, and gave me an email address to reach the tech team at regarding connecting the stove to class A. I have emailed them and will update.

I am not sure I trust him RE the single-wall, but the manual is not written clearly enough to refute it either. In any case, I want to locate the stove closer to the wall, so I would like to use a vent with better clearances.

 

[nmr]

Heard back from the tech support line.

1. Single vent was never approved. We only list b- vent as an approved method if using rigid venting.
2. If trying to tie into a class A chimney you would require a 4-inch flex which would run from the appliance to the top of the termination where the wood termination cap is located.
3. You would need to purchase a 590-930 decorative collar which affixes to the top of the appliance.
4. You would need to purchase 6-inch single wall pipe which is decorative only and to hide the flex venting which would attach to the 6-inch decorative collar at appliance and to the ceiling level where the metalbestos chimney is located. What you will need to locate is the transition piece from 6 inch single wall pipe to the metalbestos class A chimney as we do not supply this but would look similar to below and depending on the size of the class A chimney.

So single wall is not listed for use. Not a huge surprise there, but Regency should get its first line support straightened out.

I don't understand what the "wood termination cap" is. I think it could either be where the prefab chimney terminates in the ceiling above the stove, or where it terminates above the roof, I am leaning towards the latter.

So basically I think I would just be using the Metalbestos SS chimney as an expensive conduit to run a flex liner through, which is fine with me if that's the case.

 

[nmr]

Called Selkirk, asked them basically the same question: how to connect the stove. Spoke with a gentleman named Price in technical support. Notes not in chronological order:

• Me: I Have Metalbestos SS chimney, B-vent stove, both existing
• Price: Metalbestos SS was made 70s through 1983
• Price: at the chimney stop they made two adapters:
  • Stove pipe adapter (about 12" long)
  • Chimney pipe adapter (short and with a crimped end)
• Price: Single wall pipe doesn't need 18" clearance for gas, gas single-wall pipe only needs 6"
• Me: Can run b vent from chimney to stove?
• Price: Yes
  • Connect to stove with b-vent then go up and put increaser at the top, 4" to 8"
  • Low profile increaser would work, 4" to 8", part number is 4rv-i8 product code is 104308
  • Cut down the stove pipe adapter, Then use sheet metal screws to attach the increaser to the adapter

Cutting the stove pipe adapter is a little more hodge-podge than I was hoping for, but after speaking with Price I got the vibe that he knows as much as anyone about this stuff and his instructions will be as safe and as by-the-book as is humanly possible, so I plan to proceed this way.

 

[nmr]

Here is the part that Price was speculating to be a stove-pipe-adapter.

It is a 2 piece construction, looks like the two pieces may have just been glued together with RTV. The angled flange on the part roughly matches up with a similar 1/4" angled flange on the finish-support-plate. It sort of looks like this may have been designed to drop into the 8T-FSPR from above, as the flanges don't align very nicely for screws when inserted from below.

There is also pictured a 4-8 increaser which attaches to the bottom.

Here is a close up of the seam inside the adapter, the black crusty stuff is what I am thinking is RTV.

 

[nmr]

I ran the B-vent-to-chimney plan past Regency support and they stressed the need for 4" vent all the way to the outside for the purposes of draft.

When I spoke with Price at Selkirk he asked me how the existing stove was drafting. I said 'fine,' but I am not confident. I only used it a handful of times last winter, and I don't know what bad draft looks like. We have a CO detector, which never went off, and the stove always seemed to have a healthy fire that was keeping things warm. The stove is has separate combustion air input, maybe that improves the draft enough that it was never a problem previously?