Jesse Neal

I first put a 6" starter in the bottom of my barrel. Then there was a 6" to 4" adapter to connect to 4" duct.

To insulate the burn tunnel, I used vermiculite dumped in loose. To keep it out of the exhaust, I made a little divider out of stove pipe. Once the one side of the barrel was full, I filled the pipe around the heat riser with vermiculite.

It took only a few minutes to get to 300F, then from there it was a steady climb to 550.

Results...

I'm sure the temp would have kept going had I not run out of fuel. Proof positive that a sub 6" system not only works, but can generate a significant amount of heat. This was off of a 26" scrap of base trim.

Thank you so much for the help. I can post pics of how I implemented suggestions if anyone would like to see.

That's the approach I was going for. Hopefully I can get this working well enough to convince her to build a 6 or 8" system in the living room where there is more space. Either that, or reconfigure the room it is in to better accommodate a bigger system (which would require moving the chimney).

Right now I am looking for supplemental heat from my system with the added comfort of a thermal mass. I would like to help heat our 1st floor, which is roughly 700 square feet. We generally just leave the heat off upstairs until bed time, then we turn it on.

Thanks Erik. I'm going to dump in my vermiculite this evening. I think I will go with the 6" to 4" adapter on both ends and see how it goes.

I decided on a 4 inch for a few reasons. 1st, was space. I had enclosed my back porch and installed a traditional woodstove out there. It took up entirely too much room. The porch is roughly 6' deep, and my stove took up nearly half that no matter how I positioned it. My 2nd reason was availability of materials. My barrels were found, and I was on a budget when it came to the brick. The 3rd reason was to prove to the wife that RMHs are a great idea. So now I have to get this 4" system working right. I don't think she would be too keen on me tearing the whole thing down again and sourcing all new material.

I will report back once I make the changes discussed.

Ah, I get it now. I think I have another adapter somewhere.

As for the vermiculite insulation, how is that applied? I have heard some people combine with clay as a wet mix, while others just pack it tight and dry.

Thanks Erik. I am replying via the mobile site, so forgive me if my responses are off.

I was unable to get any perlite, but did find vermiculite. Is this applied dry and loose or do I mix with fireclay? I have some in powder form.

You are correct; this is a prototype with no mass yet. What do you think of increasing the length of duct without any mass? I plan to add mass later.

By "exhaust port", I suppose I do mean "manifold.' I have used a 4" starter collar, inserted directly into the back of the barrel. It sits about an inch lower than the burn tunnel. If I understand correctly, you're suggesting that I remove this and use a 6" starter instead? Would I then continue with 6" duct out to the chimney? Alternatively, what about the plenum or manifold you mentioned? I'm not quite grasping how that would be installed.

Thanks again for your input. I plan on adding mass in the spring, so I will have to report on that then.

Good morning. I'm new to rocket mass heaters as well. I just finished my first build and rebuild. My system is similar to Ben's, except that my core and riser are made of fire brick. My stove features the traditional J tube, but like Ben's is a 4 inch system. My feed tube is 6", burn tunnel is 12" and riser is 32" (all measured at their longest points). The whole thing is inside 2 16 gallon barrels put together.

I am also concerned about temperature. My highest so far has been 375F. It usually hovers between 300 and 350. I have some ideas as to what causes this.

First, my riser is insulated with fiberglass. I have an 8" metal pipe around the riser, and the fiberglass is in there. My burn tunnel is not insulated. Would covering the burn tunnel and riser in perlite help?

Second, I have a small port in the front of the feed tube. This serves as a clean out. I have a small brick that fits in the port. After my mortar cured, the gap around the plug increased a bit. I can slide paper around 3 sides of it. Is it possible this is causing problems? Seems to draft well enough.

Third, my exhaust duct ties into an existing chimney. I have about 8' of 4" duct, then an adapter to 6" where the old chimney was. Could this create too much draft and suck a lot of the heat out? After an hour's burn, the exhaust is too hot to touch, but there is only steam coming out from the stack outside.

My last target is the exhaust port in the stove. Is it possible that much of the heat is just blowing through to the outside? I feel like that may be the case, which might be caused by the change in duct size. Either that, or I need some sort of baffle over the exhaust port to slow the flow.

This stove lights and burns pretty well, I just wish I knew how to make it burn hotter. I have seen where other folks made sub 6" and claimed to have good results. Any help is appreciated. Of course, I will report back any findings to help someone else who may be in the same boat.