1" ventilated air space

[TahoeJim]

Hi.
I've been reading posts on the forum about safe stove clearance, and have a question.
Current stove is NOT installed with safe clearance. If I'm understanding what I've read so far, I can potentially get less than the generic 36" clearance by having a 1" ventilated space. (House is 2nd home 4 hrs away so I don't have access to the stove manual right now but will look up specs when I can).
Current hearth wall is stone veneer on raised (false) cement board wall as pictured. There's an enclosed hollow space between the hearth wall and the actual drywall.
This is an enclosed air space, but *I think* if I cut vents in the top and bottom, it would become a ventilated space... am I understanding correctly?
Also, are clearance dimensions measured to the nearest flammable surface (drywall/studs) or to the nearest surface (stone veneer)?

Many thanks for your expertise!

(btw, I'm also aware I need to switch to a double wall pipe because of the wood mantle... )

 

[begreen]

Clearances are measured to the nearest combustible. In this case, it would be the drywall and studs.

Is this the Hearthstone American Heritage? If so, does it have the optional rear shield attached? Does the manual permit reduced clearances per NFPA 211?

 

[TahoeJim]

Thanks @begreen . I don't know the model (will get model and manual on my next visit), but it does look most like the American Heritage (8020) photos online
It does have a rear shield attached to it.
If it is an 8020, then it looks like the heat shield will allow for 12" corner clearance instead of 18", and there is something in the manual about "With Rear Heat Shield AND NFPA 211 Protected Surface" as you mention that reduces the clearance restriction to 5" (https://1q4gfb42pami41tumh2vps5s-wp.../2020/12/hearthstone-heritage-8020-manual.pdf)

I'll admit I'm still confused about what constitutes an "NFPA 211 Protected Surface".

 

[begreen]

It will be important to identify the stove. If it's an 8020 that is an early Heritage model. The manual I have for the older American Heritage 8202 says 28" corner clearance without the shield and 18" with the rear shield. There is no clearance reduction per NFPA 211 mentioned for that stove. If it's the 8020 then 12" to the corner with the rear heat shield. If so, you may be ok without modification with what appears to be about 6" of masonry on the wall. Per NFPA 211, 3.5" of unventilated masonry achieves a 33% reduction.

The other thing to check if the stove pipe is single-wall is 18" clearance to combustibles like the mantel. Double-wall stove pipe drops this down to 6".

 

[TahoeJim]

Thanks again @begreen . I do intend to identify the stove in a few weeks when I'm back up there.
How does one stove achieve an NFPA 211 reduction and another (virtually the same stove) not earn one? I get they are different models so I'm guessing there are different materials or construction process I guess? Though I'm not sure how much the stove changed from 8202 to 8020....
And If it is an 8202 and there's no NFPA allowance then I guess it doesn't matter if that masonry wall is vented or not, right? It needs 18" no matter what?

My 'sweep's inspection also noted the mantle clearance so I'm planning on switching to double wall for that; or I need to change the mantle to stone.

 

[begreen]

How does one stove achieve an NFPA 211 reduction and another (virtually the same stove) not earn one?

Testing and documenting the results. My guess is that Hearthstone got some high demand to reduce clearances in order to be more competitive and the new version is the result. I don't know this stove well, but inside the two are quite different. The 8020 has 3 tube secondary rack and the American does not. They may have added thicker firebrick inside to reduce the radiant heat and increase the firebox temp for a cleaner burn.