Getting started, help!

Hello everyone,

I figured I would just start a thread here and see what happens.

I'm very eager to dive in and get this project started/done, I'm very certain I want to install a rocket mass heater.

But there is just so much information, I seem to be a bit overwhelmed here and need to focus myself on what I need to do.
Hopefully you all wouldn't mind getting me on the right pathway here. Please and thank you!!
1) Should I purchase that e-book on rocket stoves as a basis point here?

I will ADD to this thread information regarding my spacing as well as some pictures, so that you all know what I am dealing with.

The space I have to do this is the second half of a somewhat large Livingroom as it is 1 story here and I could easily go through the roof here for the piping out.

2) I guess pictures will help here, but there are possible problems to the layout with every spot I may pick. I would love some input on that for sure.

3) It is on wood flooring above crawl space How much of a problem is this? I saw information about doing an extra protective base layer for the wood flooring issue, as well as weight considerations. What are the initial thoughts here?

4) My Livingroom has a bunch of exterior walls, how much of an issue is this for heat loss? suggestions to offset working off exterior walls?

5) designing the rocket mass heater to accommodate heating a 1580 sq ft house...55" drum? two drums? what's needed here??

6) Are there ways to include cooking elements on a bench style primarily heater focused RMH? Do people heat a kettle off the top of the steel drum? are there ways to put other heating elements or even a small stovetop easily? Or do people generally just dismiss this as too difficult?

7) child safety...batch boxes? lid over the wood placement. fencing around hot spot...what do people do here? I'm working off a living rom that will be the movie watching hang out spot and I want to be as child friendly as I can. obviously i dont want to design and install it and think crap i should have done this this or this to change how safe it is for kiddos being about.

sourcing materials? I'm sure the book will help with this but man oh man, this seems overwhelming to me. Where do people buy steel drums? clay or whatever is is needed for the "mudding" process. I can get fire bricks and cement and piping easily enough for the most part i would think but I'd like to search, pricing out, buy everything and ready myself for project start without starting and waiting 4 weeks for a part or material to show up to my house type deal.


Any advice is most appreciated. And like I said, I will include pictures to help with layout help if interested. Thank you!!!

~Andrew




I noticed two possible additional problems is the crawl space access door is right on this corner, if I need to reinforce through the flooring (do I?) then obviously I could be blocking that access. Obviously that could be solved separately with a different access point being installed if I had to


but I love the availability of cooking components being built in and do not want to miss an opportunity to do that.
Do people cook off the top of the drum, for a tea kettle for instance? I've seen other little heating pads but not sure if it's just using the spot where the wood is inserted or not.

How about

disregard below the ~ Andrew section I was reorganizing my thoughts in bullet point and had extra unneeded writing there.

And the 8th bullet point turned into a smiley with shades, lol. sorry about that.

Welcome to Permies, Andrew!

Good to hear that you want to build a rocket mass heater. The first thing you should do to answer most of the questions you have and those you don't even know to ask yet is to buy Ernie and Erica Wisner's Rocket Mass Heater Builder's Guide. To answer more of your questions we need to know where you are located (climate), and pictures of the space. You mention exterior walls and blocking crawl space access. A RMH is best located somewhat near the center of the house, and an exterior wall is not ideal. It can be done, though. For support, if you want a horizontal mass orientation with a bench, you may be able to support it on the existing floor framing. If the mass runs perpendicular to the floor joists so its weight is spread over many joists you are most likely good to go. If it needs to run parallel to the joists and only a few joists carry all the load, you need to reinforce them. Putting a couple of concrete block piers under the middle of appropriate joists may be sufficient.

So give us more information on your desired layout and heating load, and some pictures, and we will be glad to point you in the right direction.

For a residential space where you want constant heat, you do not need more than one barrel over the riser. Tall barrel setups are good for shop spaces where you come in, heat up the space and use it, and then leave.

If you use a barrel over the riser, you can cook some on that. Certainly heating a kettle is common and easy.

For materials, the book will have a lot of detailed ideas. Craigslist or FB Marketplace are good sources for local parts.

For child safety, you can arrange the wood feed and barrel to have some masonry or cob shielding to make accidental contact more difficult. When I first built my RMH, I found that my then three year old grandkids very quickly learned "hot, don't touch". I have a 16" wide cob skirt around the feed tube of my J, which prevents any (rare) sparks from reaching the floor and eliminates casual contact with the hot feed.

That is an excellent point about which way the floor supports are running, I did not even think about that being a factor! And great info about the Hot don't touch being learned and extra cobb layering. I will take your advice on all of this. Very good stuff! and I agree on the book. I'm looking at the two 'The Rocket Mass Heater Builder's Guide' by Erica and Ernie Wisner. And Rocket Mass Heaters' by Ianto Evans and Leslie Jackson. I will pull the trigger on one if not both of those this week. Maybe the E-book for the second one I listed for $10 and the first one get a hardcopy at $28. Those prices seem reasonable to me.

The Evans & Jackson book is great for a historical perspective and low-tech ideas, though some of its recommendations are superseded by the Wisners' book which has more up-to-date info and may get you to higher efficiencies. The notion of exiting straight through the wall in particular is only applicable in certain microclimates with totally reliable prevailing winds. I would recommend the Builder's Guide for the hard copy that you can refer to frequently during building.