Adding mass to a wood burning stove

I live in a log cabin in zone 4a and heat with wood. We have a wood cookstove on the main level for cooking (obviously) that provides supplemental heat, but most of our heat comes from the big daddy wood stove in the basement. We'd love to tear it out and make a rocketstove, since they are so efficient. However, we have a mortgage on the cabin and our insurance won't cover anything that isn't certified through the Underwriters Laboratory.

So, my question is whether it would be possible to just cob around the wood stove and make a big cob hearth. Has anyone done this? Can the cob come into contact with the stove itself, or might their be unintended drawbacks I'm not thinking through? I'd love to hear any ideas, caveats, suggestions. Thanks!

It could cause the metal to get too hot if it can't shed heat fast enough. If it's in the basement, it may not help heat the upstairs much anyway. If the exhaust can go through a mass upstairs it might do ok, but there would need to be a strong draft, and it would need to be a clean burning stove to prevent creosote buildup.

Jordan Holland wrote:It could cause the metal to get too hot if it can't shed heat fast enough. If it's in the basement, it may not help heat the upstairs much anyway. If the exhaust can go through a mass upstairs it might do ok, but there would need to be a strong draft, and it would need to be a clean burning stove to prevent creosote buildup.

Thank you, yeah I was worried there might be something like that. The exhaust does currently go through a stone chimney that runs through all levels. The house has a fairly small footprint, and the floor between the basement and main level is uninsulated wood floor with a few vents near the stove. Maybe we'll just have to pay off the mortgage one of these days and do the rocket mass heater. :-/

Is your basement concrete other masonry?  If so, it already has a tremendous thermal mass.  In zone 4a, I'd be looking for ways to add insulation, seal gaps, improve windows, etc.

Gray Henon wrote:Is your basement concrete other masonry?  If so, it already has a tremendous thermal mass.  In zone 4a, I'd be looking for ways to add insulation, seal gaps, improve windows, etc.

It has a concrete floor, and it is a walkout, so it is earth sheltered, with concrete block walls on the sides built into the hill. Thank you - I'll focus on those things. That is very helpful to think about.

Here is a conventional woodstove  adapted to drive exhaust through a mass.
Turning a Wood Stove into a Mass Heater

I think surrounding the woodstove with more mass is a great idea.
I don't believe it will affected how the fire itself will burn.

Hi Rachel;  The problem with putting mass around a regular metal box stove is Warping. The metal parts of your stove will bend and curve.It will quickly quit sealing.
Unfortunately metal stoves are designed to shed their heat rapidly. They will fail after a season or two if you force them to get too hot.

A brick bell ,batch box design rmh, uses a masonry door, has no open flames and no doubt could be plumbed into your existing chimney.
Your insurance might accept a masonry stove. Some states require them to be built by a certified mason, others just send an agent by for inspection.
Worth looking into.

Here's an examples of adding cob to wood stoves

https://www.google.com/amp/s/shephersglenfarmblog.wordpress.com/2014/11/08/cobbing-a-wood-stove/amp/

No word on the long term outcome.
Maybe cob directly on the stove is a bad idea.

There are many posts on Permies about adding mass to woodstoves, most recommend stones,  pavers,  bricks  and concrete blocks around and over the the stove but not touching it.
Some suggest water in barrels or pots.
I'm keen on using the tanks from water heaters to store water in, they actually look pretty nice cleaned up, a dark smooth steel.