Chris McClellan

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since Oct 24, 2013
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Recent posts by Chris McClellan


The thermosiphon ventilation you speak of in the bench sounds like a good idea to keep the floor from overheating. Wonder though if it would also cool off the mass a lot quicker once the fire is out? Akin to not covering the feed tube once burning is complete and stopping draft from carrying the heat out of the mass.

The 4" is a PITA. Part of this experiment was to see if we wanted to go to 6" even in small spaces. With such a tall feed tube I would say probably. Eventually I hope to have a design for this that has a front cleanout, maybe even glass like the Gamera and my own edit of the Liberator. The brick feedtube is removeable for cleaning (and starting). It just sits in a groove on top of the heat riser.
The combination of different size pieces of stone in the pebble mass seems to help the mass "time release" its heat. More study will be necessary to see how the heat release works. Pebble mass and cob mass transfer heat in very different ways.
3 days ago

A couple months ago we showed you the end results of our cob mass bench build that lets us put Rocket Heaters in tiny houses and rooms with raised wood floors. Laine Wyldling has finished editing a video showing the steps of the build.

Many thanks to our generous patrons at please consider joining them for as little as $1 per month. You'll get access to more great more great fire and mud resources.  

0:00 Introduction
0:15 Preparations
0:20 New Floor
0:35 Skylight
0:59 Barrels
1:10 Cutting a 45 on a Barrel
1:45 Plans
1:59 Stovepipe Layout & Cobbing
2:33 Beginning to Dry
2:50 Overview
3:30 Gamera Rocket Heater
4:20 Closing Remarks
3 days ago

People have been asking for a followup to our Unboxing videos. How do we like the Liberator from we liked the Gen I enough to keep it for three years and buy two of them. We love the Gen II. Here's the #shorts. If you really want more details join us at where I go into more depth in my patron only videos. $1 per month supports our Fire and Mud fun.
5 days ago

In September 2020 we had another opportunity to visit our friends at and work on rocket mass heaters for their cabins. This one in the Red Shed is a combination of my CottageRocket core and Paul's pebble mass bench, plus a few new things we each really wanted to try. This heater was designed especially to heat a small space with a raised wooden floor, balancing gentle radiant heat and thermal storage with no "hot spots".

Paul was determined that we have a 1:4 height ratio between the feed tube and heat riser, while keeping the feed tube tall enough to close over the top of his standard 16" firewood. Meanwhile I wanted the pebble bench raised off the floor and lined underneath with hardware cloth to provide thermosiphon ventilation under and behind and through the heated mass to keep it from overheating the wood floor and walls.

A few things you can't see in the video: The feed tube is removeable for easy cleaning of the burn chamber. The standard CottageRocket burn chamber made of milled firebrick is lined outside and below with ceramic insulation board to keep the heat inside where it belongs. The small footprint of the heater fits in the tight space and leaves plenty of room for air circulation. Keeping the heater separate from mass allows it to be easily pulled out for inspecting and cleaning the exhaust pipes in the mass.

The standard CottageRocket uses a 2' tall "5 minute riser" design with ceramic wool compressed inside a 6" stovepipe, which works great for a 24" riser but creates too much friction with Paul's 48" Super-riser so after I ran out of time it had to be replaced with a 6" diameter cast ceramic riser, which works really well.

The 4" exhaust on the previous heater tended to get too cool to provide a good draft so this design runs the vertical exhaust right against the length of the radiant chamber to give it back a little heat to help pull the cooled exhaust through the pipes in the thermal mass. After this video was taken we added a sheet metal heat shield between the heater and the wall with a 1" gap behind it to allow natural airflow to keep the wooden wall cool.

If you like this sort of thing please subscribe to our youtube channel or support our work and get access to exclusive mud and fire content at
6 days ago
My RMH cores where they must be over wooden floors are usually built in a barrel lined on the bottom inside with at least an inch of ceramic wool then that barrel is set on a tripod of stacked bricks at least two high with a piece of sheet metal the full size of the barrel between the brick layers as a heat shield, all over a code-approved hearth board over the wood floor. Please leave a big air space you can reach into to check for hot spots on the floor.
1 week ago
Do you know if the regulatory hangup revolves around accepting the UL listing from the US or emissions testing peculiar to your area or something else?
2 weeks ago

FULL LONG BORING UNBOXING VIDEO!! We are excited to have the privilege of testing the new American made Gen II Liberator Rocket Mass Heater from before its available to the public. Heck it may not even be on their website yet! Check out what's new in this unboxing & installation video and watch us fire it for the first time.

We'll post updates as we continue to use the Liberator Gen II, so make sure to like and subscribe.  
2 weeks ago

So how does the 2nd generation Liberator Rocket Heater from fire? Nice and hot with a clean burn. Stay tuned for a full unboxing video.
2 weeks ago

What's inside the 2nd generation Liberator Rocket Heater from A heat riser and burn chamber lined with replaceable ceramic boards for starters.
2 weeks ago