Basic RMH questions

New to the forum and considering a RMH type wood heater. Here is what I have: I have a full basement that is un-insulated on the walls as well as the floors. The wall and floors are poured concrete approximately 100 years old. I currently heat with a cast iron wood stove which is terribly inefficient and uses a bunch of wood every day. The chimney is external to the house and is of recent construction. I have a wealth of old concrete residue several tons that I can use and a full pallet of recycled soft brick. I do not have access to clay short of buying it. Here are my thoughts. I will insulate the floor and the concrete wall with Styrofoam board and create a brick fascia for the foot print of the heater( front and back). I can get quickcrete partial bags for pennies from the local lumber store. My thought is to create a brick front and back and then a concrete conglomeration in the middle between the two runs of stove pipe. I would add my concrete slab fragments and pieces and then use quickcrete to tie it altogether into a solid mass. This would essentially form a trough which the stove pipe would lie in . I'm thinking that I could line this with sand creating a fully filled trough creating a thermal bridge between the fascia, the stove pipe and the concrete conglomeration in the center. I have enough concrete stepping stones to make top for the stove. This would allow for easy adjustment of the stove pipes and easy access for repairs as needed. What are your thoughts?

Steve Dalcher : Welcome to Permies.com, our sister site Richsoil.com, and a Big Welcome to the Rocket And Wood stove
Forum threads !

Please see the comments from me and a couple of your fellow members -to Rick Ford at his forum thread Hello - - - - !

Rocket Mass Heaters RMH(s),Work best when given 'Pride of Place' in the 'Heart of the Home', isolated locations, like in a Basement
do not give you the option of listening to the Rockets Roar, and feeding Your RMH to allow it to continuously run at its highest
Efficiences and Cleanest ! The Care and feeding of your rocket, installed within arms length is a totally automatic function,with no
more thought taken than you would use in adjusting your glasses -while reading ! An RMH in a remote location quickly becomes a
major interrupter of your days activities, and grows to be a Drudges Chore that you will find excuses to dodge !

Also The Basement location has problems of its own, do a Google search for the Terms 'Stack Effect' and specifically ''Whole House-
Stack Effect "

While the Thermal Mass Storage is a perfect place for your 'Concrete Residue', any portland type cement or concrete made from
it can not be used to make the Heater Core of your RMH, the High Temps 2000dF + will destroy the bonds of the lime found in all
"Portland " type concrete ! Quickcrete is a Portland type Cement ! Cob and Clay Slip are preferred materials to make a Monolithic
RMH !

There are Several high temperature products that can be used within the RMHs Heater Core, Zonolyte, Perlite, and Rockwool, but
the places where you can use Styrofoam board around a RMH is limited, and must be protected by a Reflective barrier with an
Air gap on both sides The latter is true of all Wood Stoves installations !

All sand is slightly insulating, due to all the trapped air spaces, it can be used by itself, but if used as a center fill around your pipe
it will further retard the flow of heat to and through your Thermal Mass, you may not be able to extract most of the heat energy
before it goes up the chimney !

The size of your chimney should be a good match for the size of your RMH, it is highly desirable to have the condition of the
chimney professionally checked, hopefully your existing chimney reaches a height 4 -5 feet higher than the roof of your house
and is located on the downwind or lee side of your house during your heating season .

Pretty much, clay is everywhere, and most all of it can be used within the Thermal Mass ! You should plan on some 'Fire Clay' for
the Combustion core of your rocket !

This is a little bit more negative than I set out to make it, please be sure that if there is a Rocket in your future we will help you
find it

For the good of the crafts! Think likeFire, for like a Gas, Don't be a Marshmallow, Your questions/comments are Welcome Big AL !

Al, thanks for your reply, I am well aware of the need for some type of castable refractory for the actual burn chamber and have a good supply of firebrick and a source for 3000 degree castable refractory. I have dabbled with oil burners and reil type propane forges in the past with good success. Unfortunately the basement is the only area that I can install a wood fired heater. As to the drudge of feeding it, It seems that firing once or twice a day would not be too big of an inconvenience. Additionally my workshop is in the basement and I spend much of my time there piddling with one project or another. Not looking for a perfect solution, just a good workable solution that my wood fired iron stove is not.

You have to be aware that the cold stone/concrete walls of a basement literally 'suck' the heat out of any non-ducted heating plant. Many folks in the pellet heating world are disappointed when they install pellet stoves in their basements hoping the rising heat will make it to the first and second floor of their homes…

Insulating the walls would certainly help even with your present wood burner.

Rule of thumb… install the heater where you want the heat.

Ok folks, I do understand that my setup is not ideal, however it is the only place that it can be done. I have heated with wood heat for 4 years now. I understand that the uninsulated walls and floor don't help. I go through 10+ loads of wood a year with my current setup. If i can make changes and use half that amount it will be a huge improvement. Even a 1/3 improvement would be a worthwhile investment of time and resources. Please give some constructive feedback on the heater design. I saw where a portable RMH used sand with success, I would like to expand on this concept and make modifications as necessary to make the best of a less than ideal situation. Thank you

The best thing would be to insulate those basement walls…with a RMH or a wood stove.

I have read that sand insulates too much to be used by itself for a RMH…. others will comment I'm sure.

spray foam kit, insulate down just below grade. this will seal your walls and insulate. if you want it pretty, board lath ? and dry wall.

skip the insulation on floor, let the heat climb into floor and warm your feet upstairs.

Never did the large heat sink. No room between equipment I have 80inch lathe , Cnc mill in basement, plenty to heat up.

2 garage (un insulated doors) Plenty of heat loss in mine. I ditched wood stove (tried 2cd burn with this unit) and went to Rocket/Gasser. Little dangerous to run, but cut my wood consumption in half last year.

I'm pretty sure the "uninsulated floor" referred to the basement floor. Insulating that would be beneficial especially if you have heavy/wet soil. Dry/sandy soil under the floor might reach thermal equilibrium with heat in the basement and be comfortable.

If you insulate the basement floor (and put down solid flooring on top of it), you need to interrupt the insulation at points for structural support of the heater. That will be several tons of mass which you do not want settling and shifting.

You might also consider a variation on RMH flues known as "bells". I have read about them recently, and essentially the heated gas is allowed to rise into vertical towers of mass with the exit from each at the bottom so only the coolest air escapes. This would put more heat radiating/convecting from higher points where it can serve the upper floors better.

Richard Wood wrote: spray foam kit, insulate down just below grade. this will seal your walls and insulate. if you want it pretty, board lath ? and dry wall.

skip the insulation on floor, let the heat climb into floor and warm your feet upstairs.

Never did the large heat sink. No room between equipment I have 80inch lathe , Cnc mill in basement, plenty to heat up.

2 garage (un insulated doors) Plenty of heat loss in mine. I ditched wood stove (tried 2cd burn with this unit) and went to Rocket/Gasser. Little dangerous to run, but cut my wood consumption in half last year.

Man after my own heart! I have a manual lathe and mill in the basement and a small CNC lathe and mill as well. Spend much of my free time down in the man cave! Like you looking for options to decrease wood consumption and maybe get a little more warmth. Lots of feedback on insulating the walls and floor, but not much on the heater... Not familiar with rocket/gasser... If not so messy would just go with a waste oil heater. built one for the foundry propane start and then wean onto the oil once fired up. Works really well, just messy, transferring oil and all that jazz. But it really puts out the heat. Aluminum melt too easy, thinking could melt cast iron, but not really setup for it, maybe sometime in the future.

Steve

Man cave occupied, man tend fire, good situation fire happy.

We don't like unoccupied basement builds, but with the responsible party in the space where you can conveniently keep half an ear open to the sound (and visual glow) of the heater, it is doable.

The basement insulation - definitely the big seller for this plan.
I'd be tempted to do the insulation first, put a brick heat-shield behind the woodstove, then see how things go. Until you eliminate the heat loss through uninsulated basement walls, the basement as a whole is not going to be a heat source for your upper stories past firing time, so you might as well use the existing stove as the radiant space heater it's designed to be. (the mass of those walls, and all the wet dirt behind them, is going to out-compete any conceivable heater mass when it comes to establishing a quantity of heat available. You might get some up the stairs, but mostly you'll lose it into the vast maw of the winter earth.)

The only reason to commit to heating thermal mass in the man-cave-shop is if you're working with things that need to be kept above a certain temperature, like some glues and finishes, or some delicate machinery. Then a difference of a few degrees might be huge - the difference between freezing and a successful cure, or being able to put a project on the warm bench after the fire goes out, and cut the drying time in half or better.

To insulate below the heater mass, I'd consider layering the floor with something like clay-perlite below some tiles or pavers or something. Or closed-cell foam everywhere else, and the perlite- or refractory board under the heater itself. If the basement floor is exposed into the room, it'll act as a heat sink, although it may not matter if you get the mass up on some room-air-channels or something (like the Bonny 8" plans show). Isolating the heater from the cold basement floor sounds like a great idea. A raised pad on some air-channels made of brick or paver, and then some perlite-based masonry insulation on top of that, might be both stable and effective.

As far as the brick-and-concrete trough:
The outline sounds good.
The sand is more insulating than I'd like.
My neighbors did a brick-and-cinderblock trough (brick facade on the room side only), brick heat shield going out, and filled with the local mineral soil, just dampened and tamped into place - packs a little tighter than a graded sand, and it's working pretty well. Better than Paul's pebble-style or the sand-prototypes I've seen, not quite as well as a solid mass, but you can't beat the price in time and materials as far as fill dirt goes.

You could also prototype it with sand, knowing that you're not likely getting the heating temps you'd prefer, and make sure it's working robustly. You'd want the exhaust temps slightly high (over 200 F), and then if you want better efficiency you replace the sand with cut pavers and mortar, or clay-sand infill, or whatever. The greater conductivity of a solid infill material will suck up more of your heat from the exhaust, but by then the greater part of the mass is already dry and warm, and you should be able to get reliable performance from the proved-out heater layout.

I suppose you could also just dampen the sand a bit, if you can do so without causing major mold problems behind the new insulation in that basement.

That's another consideration with this whole scheme: the spray-foam insulation may be key because if you have air movement between the insulation and the cold walls, you'll almost certainly trap condensation back in there, and get mold. Either seal it completely, insulation to wall, or leave plenty of ventilation to remove condensation. I think I'd vote for seal it completely, except that synthetic foams are a little off-putting from the toxic gick standpoint, but others may have more experience here.

-Erica W