Adding a mass to the Liberator rocket stove

We bought a Liberator rocket stove last year and used it all winter to heat 1200 sq. ft. It had a bit of a learning curve. I had flames coming back up the feed tube and when I threw the cap on that, they shot out the side vent a good foot or more!  Scared the crap out of me!  It also made me realize just how leaky the system is when you have smoke pouring out of every seam on the stove and the chimney pipe.

Other than that, it's an amazing heater as far as pellet stoves go. One 40 pound bag lasted 11 hours if we let it burn straight through. It burns kindling great as well but be prepared to feed it every 20 minutes. That brings me to the point. We are getting very confused as to whether we can add a mass to this thing. We bought it with every intention of turning it into a mass heater, but words from the wise and mighty Paul have us shying away from that now. He warned us (at the Thrivalist Fair in Addy, WA) that our little stove doesn't have a large enough feed tube/burn tube to make a mass heater work.  It made sense at the time, but pouring over Uncle Mud vids and the RMH forum makes it look like there's no reason why we can't build one, as long as we stay within the manufacturers guidelines for numbers of 90s and horizontal length.

Does anyone have a Liberator with a mass? If so, what did you build (materials, size, etc).

This is the current set-up.

I would love to have a Liberator if I didn't live in a tiny house that is already too full to add anything else. Though, I am a big fan.

Here are some suggestions for adding mass.

Sky said, "Chris "Uncle Mud" also did a lot of work in figuring out various ways Liberator Rocket Heaters can be integrated into thermal mass and has an excellent video series on the subject.

https://permies.com/t/162648/EPA-Approved-Rocket-Mass-Heater#1467510



https://permies.com/t/156323/Uncle-Mud-Liberator-Rocket-Mass



I hope you will find some of this beneficial.

We are building an ecovillage here in southern Nova Scotia, Canada, and were hoping to use the Liberator rocket stove heater with a thermal mass bench (by a certified mason).

The rules are strict here and insurance will NOT cover this unless it's certified or built by certified/qualified persons. We would love to have every home include a RMH, if possible.

I'm interested to hear more about if anyone else has done this too, what their experience was like, and what challenges were overcome, if any?

So quick question having some time with the liberator do you still see it as a viable option.i live in Nova Scotia been thinking of adding one to my house

Yeah it’s the only one that would be legal here in NS because of its being manufactured and its rating. But be prepared to double check with your insurance company first. Just be sure and frame it verbally as a “pellet stove”, not a RMH!

I am also curious about this.  We are in central Kentucky  and have a Liberator, but no mass attached yet.  I had a similar experience in that we needed to feed it about every 30 minutes or so, and without the mass it quickly cooled off during our chillier nights here when it reached 0 to 10 F.  I was also planning on adding a mass this summer/fall, but am having doubts as to whether or not it will have a big enough impact. Have any experienced rocket mass folks besides Uncle Mud used the Liberator?  Will adding a mass make a big enough difference with a stove this size?

I am considering pulling it out and adding a traditional wood stove or attempting to build a custom RMH.  Any thoughts or feedback would be appreciated!

Hi Michael;
Adding a mass would help, but loading every 30 minutes is excessive.
My 8" J-tube only needed feeding once an hour.
If you can have a Batchbox RMH then build one this summer, you will not regret it!
My 6" batchbox burns for 2hrs and has coals for another hour.

Hello, How long does it take to fully load this mass with heat and how long does the mass continue to radiate heat after the burn?
Looks nice!

I have seen some videos but having a hard time finding more specific details regarding the best mass materials and how to use them in building a mass around the exhaust pipe and partly around the manifold area without risk of spalling as per manufacturer guide in the manual.

I have to decide what to do in my basement as winter comes in Nova Scotia. I have a concrete slab basement with an existing chimney and old cleanout hatch door access through a masonry brick wall. If I can't get settled on a plan for mass using materials I have access to then I will end up having to spend my first winter without a mass at all and my backup heat is electric baseboards and an aging heat pump... not sure how hard that will hit my wallet!

Thanks, James

Hi James. In my experience a cob-and-rock mass roughly the size shown takes a good 4-6 hours of steady burning to fully charge, and then it will comfortably radiate warmth for 12-24 hours depending on insulation and how cold it is outside. One thing to watch in a basement: the concrete slab and foundation walls will drink up heat, so I would put insulation between the mass and any concrete or exterior wall to make sure the warmth goes into your living space instead of into the ground.

Mikael Korhonen wrote:Hi James. In my experience a cob-and-rock mass roughly the size shown takes a good 4-6 hours of steady burning to fully charge, and then it will comfortably radiate warmth for 12-24 hours depending on insulation and how cold it is outside. One thing to watch in a basement: the concrete slab and foundation walls will drink up heat, so I would put insulation between the mass and any concrete or exterior wall to make sure the warmth goes into your living space instead of into the ground.

Definitely yes on the insulation between stove/mass and a bare concrete slab. The mass shown above does not cover any of the manifold. My logical assumption is the 4-6 hours burn to fully charge a cob-and-rock mass roughly the size shown may be reduced by ##:## (no overfiring just following general manufacturer specs). Again being mindful of how much of the manifold area can be safely covered without risk of spalling or operating outside any manufacturer recommended parameters. Input from anyone with such experience is appreciated. Maybe Uncle Mud has something to say here.

What dimensions is your mass?
What material is your mass?
How long to fully charge (or heat up) to what you feel is the max capacity of your mass?
How long roughly would you say that mass radiates heat after fully charged and the burn has finished?

Michael Blum wrote:I am also curious about this.  We are in central Kentucky  and have a Liberator, but no mass attached yet.  I had a similar experience in that we needed to feed it about every 30 minutes or so, and without the mass it quickly cooled off during our chillier nights here when it reached 0 to 10 F.  I was also planning on adding a mass this summer/fall, but am having doubts as to whether or not it will have a big enough impact. Have any experienced rocket mass folks besides Uncle Mud used the Liberator?  Will adding a mass make a big enough difference with a stove this size?

I am considering pulling it out and adding a traditional wood stove or attempting to build a custom RMH.  Any thoughts or feedback would be appreciated!

Michael,
The Liberator produces about 30,000 btu per hour burning kindling, and 20,000 more or less on pellets. I strongly recommend the best, tallest insulated chimney you can get, blast gates on the 4" air intakes to control the burn, and a 6 to 12 foot mass with 12 feet of heat exchange pipe in it for a good balance between mass heat storage and draft. I like a cob mass around 18" tall, 18" to 24" wide, insulated or isolated from the floor with thermosiphoned air movement,  with the pipe no more than 4" from the top and front surfaces of the mass. If the mass is any bigger the Liberator never quite gets it warm and you get condensate and poor draft. The Liberator didnt draft as well with stratification masses unless you have a really tall insulated chimney. --Mud

Chris McClellan wrote:

Michael Blum wrote:I am also curious about this.  We are in central Kentucky  and have a Liberator, but no mass attached yet.  I had a similar experience in that we needed to feed it about every 30 minutes or so, and without the mass it quickly cooled off during our chillier nights here when it reached 0 to 10 F.  I was also planning on adding a mass this summer/fall, but am having doubts as to whether or not it will have a big enough impact. Have any experienced rocket mass folks besides Uncle Mud used the Liberator?  Will adding a mass make a big enough difference with a stove this size?

I am considering pulling it out and adding a traditional wood stove or attempting to build a custom RMH.  Any thoughts or feedback would be appreciated!

Michael,
The Liberator produces about 30,000 btu per hour burning kindling, and 20,000 more or less on pellets. I strongly recommend the best, tallest insulated chimney you can get, blast gates on the 4" air intakes to control the burn, and a 6 to 12 foot mass with 12 feet of heat exchange pipe in it for a good balance between mass heat storage and draft. I like a cob mass around 18" tall, 18" to 24" wide, insulated or isolated from the floor with thermosiphoned air movement,  with the pipe no more than 4" from the top and front surfaces of the mass. If the mass is any bigger the Liberator never quite gets it warm and you get condensate and poor draft. The Liberator didnt draft as well with stratification masses unless you have a really tall insulated chimney. --Mud

Hi Chris,
I am trying to decide if I really need to purchase a double wall pipe liner for my Liberator installation or if it makes more sense (and saves on extra work with extra costs)  for me to use a single wall pipe installed professionally into my existing brick chimney which appears to be lined with typical clay flue liners. When I read online posts on the Liberator installation or on pellet heaters there is often talk of a double wall insulated pipe being superior (or highly recommended) for getting a good draft. I'm not seeing comprehensive conclusions though when it comes to making this choice where the install site already has a brick chimney lined with typical clay flue tiles. Understanding there are variables to consider such as inside diameter and clearance or condition (damaged tiles, globs of refractory mortar etc.). Maybe it is a good, better, best situation with clay, single or double wall retrofit then it comes down to inside diameter and condition of my clay liner coupled with my budget.

I may have misunderstood all the reading I've done including the manual where I now believe the diameter and insulation of the flue is paramount to achieving proper draft.

Page 7 of the Liberator manual paragraph 2 states "Use a solid insulated listed factory built chimney length..." so I think after reading this a few times now I am understanding this insulated length is only the short pipe that mounts at the top of a brick chimney up on my roof. So now I'm unsure if a steel liner retrofit should be used at all. Googles AI result on topic "clay flues are often much larger than 6 inches. An oversized flue causes sluggish drafts, poor combustion, and heavy creosote accumulation for a high-efficiency stove". This is inline with what I thought about the need for strict adherence to the 6" pipe recommendation.

I sincerely wish I could just trust the installers but there are few in my area of Annapolis Valley Nova Scotia and I have good vibes from only 1 out of 4 contacted so far.

Thank you,
James

Hello,
Using insulated pipe for all vertical chimney extending to at least 2 feet above your highest ridgeline will give you the best draft. Go higher if you have deep snow. An existing terracotta lined masonry chimney will not perform nearly as well and should probably be a lot taller to compensateat least a little. It will have mass working against you for a slow start and it will absorb more of the heat energy that should go into creating more draft for a hot clean efficient fire. If you have room inside your terracotta lining you can drastically improve a masonry chimneys performance by installing a 6" stainless steel flex liner wrapped with the proper insulation. I find a lot of these liners on Facebook marketplace and such sites for a lot cheaper than insulated pipe because people changed their minds or never got around to installing the liner or a new homeowner doesn't want it.

Chris McClellan wrote:Hello,
Using insulated pipe for all vertical chimney extending to at least 2 feet above your highest ridgeline will give you the best draft. Go higher if you have deep snow. An existing terracotta lined masonry chimney will not perform nearly as well and should probably be a lot taller to compensateat least a little. It will have mass working against you for a slow start and it will absorb more of the heat energy that should go into creating more draft for a hot clean efficient fire. If you have room inside your terracotta lining you can drastically improve a masonry chimneys performance by installing a 6" stainless steel flex liner wrapped with the proper insulation. I find a lot of these liners on Facebook marketplace and such sites for a lot cheaper than insulated pipe because people changed their minds or never got around to installing the liner or a new homeowner doesn't want it.

Thanks for that reply. My chimney guy was here today and says the clay liner will need to be removed to make room for a steel liner with 6" inside diameter. Now that this is settled I am just waiting for him to contact Liberator for opinion and guidance on if my operational  performance should then be satisfactory with a rigid smooth single wall steel liner insert properly enclosed top and bottom or if I should go ahead with double wall insulated (provided I will have space once the clay tile flue liners are removed).
- James

James Po wrote:

Chris McClellan wrote:Hello,
Using insulated pipe for all vertical chimney extending to at least 2 feet above your highest ridgeline will give you the best draft. Go higher if you have deep snow. An existing terracotta lined masonry chimney will not perform nearly as well and should probably be a lot taller to compensateat least a little. It will have mass working against you for a slow start and it will absorb more of the heat energy that should go into creating more draft for a hot clean efficient fire. If you have room inside your terracotta lining you can drastically improve a masonry chimneys performance by installing a 6" stainless steel flex liner wrapped with the proper insulation. I find a lot of these liners on Facebook marketplace and such sites for a lot cheaper than insulated pipe because people changed their minds or never got around to installing the liner or a new homeowner doesn't want it.

Thanks for that reply. My chimney guy was here today and says the clay liner will need to be removed to make room for a steel liner with 6" inside diameter. Now that this is settled I am just waiting for him to contact Liberator for opinion and guidance on if my operational  performance should then be satisfactory with a rigid smooth single wall steel liner insert properly enclosed top and bottom or if I should go ahead with double wall insulated (provided I will have space once the clay tile flue liners are removed).
- James

A single wall liner inside a terracotta chimney would work. If you have room add an insulation wrap, but I would try not to break up a good terracotta unless absolutely necessary.

I put solid stainless steel liner inside the old terracotta chimney liners for new wood stove installations, and poured perlite into the cavities (after blocking the bottoms), and that insulates them nicely without tearing out the original liners. Much less expensive, too.

Glenn Herbert wrote:I put solid stainless steel liner inside the old terracotta chimney liners for new wood stove installations, and poured perlite into the cavities (after blocking the bottoms), and that insulates them nicely without tearing out the original liners. Much less expensive, too.

Hi Glenn,
This is also suggested by Liberator. If the clay  liner allowed a 6" inside diameter pipe and my chimney guy was ok with pearlite I would be OK with that (provided we can get the pearlite). Initial inspection looks like it is just a bit too tight. I'm going to have a final decision before the week is done.
- Thanks, James

Wow, that is a small TC liner :O
I had a 12 x 12 which was so big I added an 8" galvanized duct outer skin to fill around the 6" SS to avoid spending a ton of money on perlite, and an 8" TC which was a tight fit for the 7" SS I used to allow for a future 7" batch box RMH. (I had to slightly flatten the four sides of the 7" SS to fit it into the 8" TC.) My experience with terracotta flues is that an 8x8 is about 6 1/2" to 6 3/4" square inside.