Alcove digest

[rustyneil]

Hi folks, I'm a new member in the process of converting a masonry fireplace and chimney in an exterior wall into an alcove for a freestanding wood stove. Reading through many posts here has been very helpful and I'm grateful for all the knowledge that has been shared. Before presenting my own project for feedback I thought I'd try to summarize what I've learned about alcove construction in general - both to correct any misunderstandings and hopefully offer a useful starting point for others.

Stove considerations

• make sure the stove is approved by the manufacturer for alcove installations, with documented clearances in the manual.
• if possible, submit plans to the manufacturer for them to review and approve.
• convective stoves or soapstone and other heat retaining stoves tend to be better suited for alcoves because of lower radiant heat.

Clearances

• This essential hearth.com primer summarizes the need to pay careful attention and adhere to all minimum clearances for stove and stove pipe.
• heat shields may facilitate reduced clearances per NFPA 211 guidelines if allowed by the stove manufacturer and local building codes. Most stove manuals allude to these guidelines but don't offer much specificity. See wiki on NFPA wall clearance reductions.
• masonry or fully non-combustible alcoves may have greatly reduced clearances if they are freestanding from any combustible materials.

Alcove geometry

• The general advice seems to be to avoid putting stoves in alcoves if possible because of reduced air flow around the stove and reduced radiant heat to the room.
• Alcove designs based on aesthetics, space limitations, or other concerns will need to balance these considerations with reduced thermal performance.
• the bigger and more open the alcove, the better.
• like any stove, the more centrally located within the house, the better.
• the further forward the stove can be located within the alcove, the better.
• Don't let all the pretty pictures of alcoves you see online skew your expectations - just because someone built it and it looks good doesn't mean it's functional or safe!

Materials

• alcoves should be constructed with noncombustible materials wherever possible.
• best practice is to construct walls as heat shields around the stove to protect adjacent framing and combustibles (see 'clearance' refs above). This often involves an air gap within steel studs supporting durarock and a noncombustible finish. An air gap at the top and bottom of each wall should facilitate uniform air flow around the entire perimeter. Metal plating or sheeting can also be used. Ceilings may also require a heat shield.
• Wooden mantels are a potential liability and must meet clearances for combustible materials. Metal heat shields covering any mantel surfaces facing the stove may reduce minimum clearances. Noncombustible mantels are preferred.
• Where the alcove is part of the building envelope, appropriate noncombustible caulk, insulation, and other materials should be used to create air, vapor, and thermal barriers. This wiki on chase construction may be useful.
• Receptacles in an alcove aren't a big concern as a combustible, but they should be installed as far from the stove and as close to the floor as possible along the alcove perimeter and use metal plates and conduit.

Ventilation

• For heat shields, air must be allowed in around the bottom and it needs to be able to exit through openings across the top.
• Higher lids above the stove are preferable for safety and better air circulation.
• Where the alcove lid is higher than the mantel or facade, some form of ventilation is necessary so the space doesn't overheat.
• Passive ventilation is preferable to fans or other mechanical ventilation when power outages are a concern.
• Improving air circulation is best achieved by conveying cold air to the stove rather than trying to blow warm air away.

This is a quick first pass at a digest of alcove design considerations. I'm new to this work. No doubt I've missed considerations that others might add -- or mistaken considerations that others will correct. Thanks for any input!

Here are the threads I found most informative. Any essential ones I missed?

1. https://www.hearth.com/talk/threads/converting-an-open-hearth-to-stove-in-combustible-alcove.200502/
2. https://www.hearth.com/talk/threads/alcove-design-for-wood-stove-in-icf-house-feedback.197043/
3. https://www.hearth.com/talk/threads...-build-for-hearthstone-mansfield-8012.199128/
4. https://www.hearth.com/talk/threads/converting-an-open-hearth-to-stove-in-combustible-alcove.200502/ (stove considerations)
5. https://www.hearth.com/talk/threads/zc-fireplace-to-alcove-conversion.205821/ (stove considerations, clearances)
6. https://www.hearth.com/talk/threads/wood-stove-within-not-in-front-of-existing-fireplace.204838/ (stove considerations, clearances)
7. https://www.hearth.com/talk/threads/another-alcove-build-advice-and-input.202453/ (stove considerations, clearances)
8. https://www.hearth.com/talk/threads/mantel-above-alcove.207594/ (mantel)
9. https://www.hearth.com/talk/threads/alcove-question-for-lopi-evergreen-ii.188120/ (ventilation)
10. https://www.hearth.com/talk/threads/my-alcove-needs-a-top-what-would-you-do.199117/ (ventilation)
11. https://www.hearth.com/talk/threads/fan-in-a-stove-alcove-wall.163574/ (ventialtion)
12. https://www.hearth.com/talk/threads/alcove-insulation.198447/ (ventilation)

 

[EbS-P]

Stove considerations

• make sure the stove is approved by the manufacturer for alcove installations, with documented clearances in the manual.
• if possible, submit plans to the manufacturer for them to review and approve.

Well…. UL has new testing requirements. The short, some/most?? manufacturers have completed testing for the new standard. As a consequence an alcove installation may not be approved.

If your alcove width is fixed choosing a stove that meets your opening requirements would be top of my list. I’m not sure how successful you will be getting any one off approvals from the manufacturer.


Good luck! I would almost always opt for the easy route and choose an insert.

 

[rustyneil]

Well…. UL has new testing requirements. The short, some/most?? manufacturers have completed testing for the new standard. As a consequence an alcove installation may not be approved.

Thanks much for your input. I appreciated the photos you shared of your alcove installations in one of the other threads.
I saw the comment by BKVP addressing the new alcove testing requirements (and lack of results in general). I decided to purchase and design around a Hearthstone Green Mountain 60 because it specified alcove clearances and seemed as safe a bet as any. Helps that both local installers I spoke with carried and endorsed it - and my wife really likes the look. Fwiw I did post the plans for my install here and would welcome any feedback.