Chris McClellan

B Haring wrote:I have a Liberator Rocket Heater that I was planning on paring with a similar style 9' straight bench.  How has this half-barrel bench worked in the long term?  Still happy with it?  Just listened to Paul Wheaton and Matt Walker's RMH Smackdown where they mention they don't recommend running the exhaust out the end of the bench any more.  

Any feedback would be greatly helpful!

To add some context to my situation - I have had the Liberator for 6 years now sitting in my basement and finally have the timber frame addition to install it in.  I had the floor joists designed to handle the weight of a masonry heater (basically, the engineers designed it to carry a 3x3x12 chunk of concrete).  I am restricted by where the beams are for the location of the chimney.  I could put the Liberator on either side of the bench, but the side with the chimney would require the pipe in the bench to do 180 degrees, right?  

Mud's half-barrel design seemed to be simple and forgiving for a beginner.  

The half barrel design is an excellent pairing with the relatively low power output of the Liberstor (about 30k btu per hour max). My experience is that the Liberator doesn't produce enough heat to warm a whole 3x3x12 mass so it never gets warm enough to heat the house well. If you surround a heat exchange pipe or barrel with too much mass it starts behaving more like an insulator. I also like to exit my chimney through the top of the bench leaving the horizontal capped end of the tee exposed for easy priming and cleaning. --Mud

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.

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.

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

M Pearson,

The Cob Hat is an evolution of the smaller hat on a rocket I built in a school bus in 2013.  My CottageRocket design I started using in 2016 has the mass inside the barrel(s) surrounding the core. As you guessed, we can store a lot more heat per mass where we can get the mass hotter. 200 to 400 pounds of mass reaching 600 degrees (f) or more in a CottageRocket core does about as well as a 2000 to 4000 lb mass bench that only reaches an average of about 130 degrees (f). It was designed to heat my daughter's treehouse without collapsing the wood floor (or setting it on fire) but we ended up using the first CottageRocket to heat our 1200 square foot doublewide trailer in Cleeveland Ohio for three years. If the house is big enough to hold a 5 ton mass bench it is probably too big to keep warm over night with a CottageRocket, but it works great for a cottage or bus or trailer. The Cob Hat combined with a small mass bench is a great combo in a Tinyhouse partly because a rocket heater with a fully exposed barrel will heat the room up before the mass is fully charged, so people stop feeding the fire early and wake up cold.    

James Fox,
Thank you for sharing your fantastic work. Your glass is so much better than doom scrolling my phone. I didnt think i was looking forward to it getting cold enough to light my rocket, but now I am a little bit. --Mud

Tim, install a rocket exhaust to the same code specs as any other wood burning heaters. The rules are there to reduce sudden over the roof downdrafts as much as any other reason. Rockets can be more susceptible to downdrafts.

Sandee,
Howdy neighbor. It is possible. Supporting the weight may require adding structural support or at least spreading the load across multiple beams and joists, and compromising on how much mass storage you build. My CottageRocket designs use less mass placed closer to the core so the mass is hotter so it stores more heat than a larger mass further down the exhaust stream. Insulating and sealing the space can also help a lot--Uncle Mud

May,
There are generally two kinds of fireplace. The first is a site built masonry (brick or stone) unit with a brick chimney, hopefully lined with flue tiles. This type can has a stainless steel liner installed in it to allow a woodstove or fireplace insert to be installed in it. I have used such a setup to install a ricket heater and bench in the room. The rocket and its mass bench can be installed on the hearth if there is room or on the floor nearby if the floor can handle the heat and mass. The rocket is not installed in the fireplace, as that would limit the transmission of radiant heat.

The second kind of fireplace that is more common these days is a "zero clearance fireplace" it is an appliance designed to look like a brick fireplace but it has a metal chimney and framework (not masonry) and can't take an insert or woodstove or rocket heater.

I have installed rockets and woodstoves and inserts in fireplaces and using their own insulated stainless steel chimney. The performance (draw) of an insulated stainless steel chimney is vastly superior. It is possible if you have a zero clearance unit you could replace the whole thing with a stainless steel chimney and a rocket heater.

Whatever you do please do not alter anything without having the chimney inspected in person by someone who knows what they are doing. --Uncle Mud