Adding Thermal Mass Around Wood Stove

Is it helpful? Is it safe? Is it smart?

Have you heard of a rocket stove?  I’ve done some experiments and builds with Rocket Stoves.  One of the primary goals of a rocket stove is to “bank” as much heat as possible inside your structure before sending what’s left out the chimney.

So, I was wondering… Why not apply that concept to my garage wood stove?

  • Will it hurt my woodstove?
  • Will I burn down my garage?
  • Will I steal so much heat that I will have draft issues?
  • If I have draft issues, can I offset them?
  • Will I notice any benefits?

About My Stove (Drolet Savannah)

It’s a fairly cheap stove.  Not high end.  It is approved for mobile home use so I already know that I can push my luck on the clearances a little and I’m not as concerned about damaging the stove as I would be with a $3-6 thousand dollar stove.   The stove starts slow with poor draft and then escalates to a very hot burn, even when the air adjustment is all the way closed.

The stove achieves it’s decent efficiency rating by burning very hot, which means clean, but it’s not necessarily easy to slow things down and get a long burn.

The garage insulation isn’t awesome so I want to bank the heat into some dense thermal mass as quickly as possible, so I’m testing concrete blocks very close or touching.


I want the bricks to get very warm or hot all the way through after 6 hours of burning.  I will watch the stove very closely to study how it’s burning, how draft is effected, and if any potential for stove damage becomes evident.

Version 1

Too much mass on the sides, not enough up above. Lower bricks aren’t hardly getting warm and outer side bricks are much cooler than the inner ones. I want hot bricks everywhere, exposed to open air.

Version 2

Much better though still too much mass in some places. I’m going for all bricks HOT after 6 hours of firing the stove.

Version 3

This is looking promising! All the bricks are very hot after burning the stove about 6 hours. I may even add an additional brick or two against some of the surfaces that are too hot to touch.


Bricks stacked all over the top of your woodstove is definitely overkill.  This is a test though so I want to try everything.

Pipe Dream?

Garage is cozy, now what about my greenhouse?  I want to keep temperatures comfortable in my wood-stove-heated garage.  I am also trying to heat my greenhouse in Iowa via insulated ducting buried underground a short distance between the garage and greenhouse.  So, I’m stealing the garage heat and sending it to it’s oblivion in an un-insulated greenhouse.

The greenhouse was already in full production when I installed the ducting so burying it under the beds wasn’t an option. Instead. the duct pops up in the greenhouse like a submarine periscope and is fitted with a centrifugal fan that is controlled by a speed control and thermostat.

It’s cold here in Iowa and it’s unlikely that the air I’m piping in there will be hot enough to offset the lack of insulation and intense cold I’m dealing with. If I can get just one Bhut Jolokia (Ghost Pepper) to ripen in December this year, then I’ve done something pretty remarkable. The leaves are dropping off the hottest peppers now but the kale, chard, celery, greens, and herbs are loving it.

Next step is to bring the ducting right up next to the wood stove and possibly even attach the duct to a cavity in the thermal mass around the stove or attach it to a heat reclaimer like the magic heater. This will require an additional 30 feet of 6″ ducting which I will most likely need to insulate in order to make sure that it’s able to deliver that warmth all the way to the green house.