So my wife is a member, but I thought I would join as well.
I have an old stone farmhouse (late 1700's early 1800's). We had a blaze king princess free standing stove, but let's just say I was underwhelmed by its performance as well as the fragility of the catalytic combuster.
Ive got a fireplace alcove to use. It roughly measures 51"Hx51"Wx30"D.
I was going to have a custom wood stove fabbed up to fit in the opening. (w/glass doors, I like watching the fire)
But my wife wants a rocket mass heater.
I've been trying to think up some combination. I would like the stone walls of the fireplace to act as the mass.
Hi Jerry. Thanks for signing on the dotted line for your rocket scientist apprenticeship. :)
As Davin pointed out, a batch box sounds like its what your looking for in order to have a good view of the fire. The traditional J tube design only allows you to see the fire when your right above it peering down into the firery blaze of the feed tube, whereas a batch box has a door with glass similar to a standard conventional wood stove.
I have seen some other threads that have taken on a very similar project utilising a fireplace alcove and will post them if I can find them.
I think the alcove turned into being a bell chamber with a batch box core inserted into it sharing the same space.
A good place to look at becoming familiar with batch box designs is here: batchrocket.eu
Let us know if this is along the lines that you had in mind so we can help direct you the best way we can.
That's an interesting design, I'll definitely have to look into it some more.
I don't really have an idea what would work best. I loved having a roaring fire in the blaze king, but could never get enough heat out of it. She loves the cob benches of a RMH but I dont really have any way of doing that unless I make a hole in the stone wall.
I am currently heating cast iron radiators with a coal boiler, it does a great job of heating the house. But if the power goes out, there goes my heat.
I would love to incorporate some piping to circulate water to my radiators as well, if possible.
As your opening is 51", the core could be built off to one side and the bench could start at what's left of the opening. You could continue a stratification/bell bench from here.
If you were to draw up some pictures and take some measurements of the space, we can get a better idea of what your working with.
Also information on your house would be important. How big is it, construction, insulation if any, how compact or spread out is it... And what size is the chimney and how tall is it, and interior or exterior. Is the stone alcove above a basement or crawl space? How easy would it be to get in and reinforce the floor?
With that we could advise on what size of system would be best.
16"-18" stone walls in the process of repointing with
natural lime morter, no insulation.
Fireplace alcove is on the 1st floor. I poured a concrete hearth the 1st year we were here, and the fireplace foundation goes down to the basement and is massive.
6" stainless flexible pipe up the old stone chimney, interior of the house. Measured from the hearth, it's around 27' to the chimney cap, so maybe the chimney is around 21' long.
Is the alcove/fireplace on the exterior wall or is it in the center of the room? I read through comments, but still not sure. The performance of the heated mass (stones comprising the alcove) in heating the house would depend on that location.
It sounds like you have hydronic heating now (radiators, and I assume hot water, not steam ?) driven by coal. If you have "extra" space, you can put a lot of mass into that system simply by installing (insulated) storage tanks and keep 500 gallons or so above 160F. This would be of interest from two standpoints: 1) your burn times could be short and hot rather than continuous; 2) The stored mass would deliver usable heat to the radiators w/out any burn for a certain extended period of time depending on the size (volume) of the mass. Variable speed circulators and t-stats on each radiator determine how much heat is provided in the building (drawn from the mass). This is mature tech and available off the shelf - maybe even the system design. Radiator 'stats have been the go-to for 30+ years, especially in Europe - both hot water and steam systems.
You mentioned power outages. Today's pumps are very efficient relative to even 10 years ago. The whole distribution and control system might run on less than 1500 watts using recent pump tech - maybe much less. Of course that's just a wild guess, not knowing anything, really about your system. And that's begging the question of how the coal boiler is fed. It sounds like you have one of the few remaining operating small coal systems in the USA. You might garner a bit of interest and potentially helpful input and contacts for that system at "heatinghelp.com" on their forum, "The Wall". They're cutting edge, but they like old systems and have some membership expertise.
Others will need to answer whether you safely and effectively put a heat exchanger somewhere in an RMH to pull out the high BTU's needed to store heat in a hydronic system. It may be that it would need to be designed as a dedicated RMH. I'm not sure the physical build requirements of a hydronic heat exchanger can be combined with a "normal" RMH, which, I believe, is essentially a convection system heated by combustion exhaust from the burn chamber; the burn chamber itself provides radiant heat to the nearby area, but benches and massive ducting carry the heat to areas farther from the RMH before exhausting it from t he building.
Sounds like you have a wonderful little project! Thanks for sharing.
My hydronic system is about as good as it can get, trv's on each radiator, constant circulation, etc. I've done a lot of researching and talking to others on storing heated water, and the consensus is to leave the heat energy in to coal.
The fireplace is an interior wall, the room dimensions are roughly 21'x24' A kitchen addition was built on the other side of it that wall.
She really wants a cob bench, so I'm just going to have to move some stones.
The bread oven is just an idea, I think I have a lot of space to utilize.
Hope this simple drawing helps. I could create an 8' long bench off to the right for more thermal mass.
A concern is that the high Temps will affect the lime mortar of the fireplace. So I would need to coat the stone work with ??? material to slow the heat absorption I'm thinking.
There are a number of people who have posted about putting one in their basement. So you might want to search out some of those threads to see if their solutions would mesh with your realities. I don't know anything about it, other than the admonitions I hear to avoid the situation so hopefully the experts chime in to provide further info.
If I am reading this correctly, your thoughts on an 8' bench to the right will absorb enough of your heat that when it gets back to your chimney /fireplace it will have cooled enough that your old mortar should hold up well.
If you are thinking of building a batchbox there should be plenty of heat to attempt a pizza oven.
Although I would leave that feature out to begin with. Just get your RMH figured out and working first, then if desired you can go back and modify things to bake pizza.
I've built a rocket mass in the basement. It does heat up the upstairs by just the heat from the barrel, but it is supplemental, unless you are feeding it all day. On my days off this winter I ran it all day and held the upstairs in the low 70s. I had vents cut into the floor to let the heat naturally rise plus the stair way. Over all I went from using three tanks of propane to only using just over one, and that's because I ran out of firewood. The basement would start at 69 degrees when I got home, to close to 90 degrees within 3 hours, plus the mass isn't fully complete from the cob. I'll be doing some small changes but overall I'm pretty happy with it.
If you have a way to build the heater to the left of the fireplace, run the exhaust to the right, then wrap it back to the chimney, it should give you a nice bench to sit. I would try to run the pipe close to the stone so it will work as part of your mass. Can you take a picture farther back to see the room better? It would help the mass design ideas.
How sturdy is the floor around the stone enclosure? Could you add posts under the floor without interfering with basement use? A cob bench spreads the load out enough that a sturdy floor can generally support it. A cob/masonry bell concentrates the load enough that it needs its own foundation.
If you do want a radiator barrel for instant heat, that can probably go on the floor next to the stone box (with appropriate air space and insulation.) Then you can make whatever bench arrangement you like, ending with the stone box as the final bell before going up the chimney. There are airflow and other details we can advise you on if you want to go that route.
With the stone box opening 51" high and wide, you could actually recess a low bench partly into the opening for a cozy seat for two, as long as neither of you is extremely tall Then you could extend a bench to one side for more seating in the open. It looks like the hearth extends 25" in front of the stone box so a bench could easily be supported on it.
You mention wanting to integrate with your state-of-the-art hydronic radiator system; I think the safest way to do that would be to incorporate in the bell a 10 gallon or more water tank at atmospheric pressure, with float valve for makeup to keep it full, and run a coil from the hydronic supply (before the furnace) through the tank to pick up heat. Then route the pipe back to your furnace so it can come on if the RMH tank is not providing enough heat. With your individual radiator thermostats, the part of the house warmed by the RMH will not call for radiator heat, and remote rooms can be hydronically heated.
Oh sure, it's a tiny ad, but under the right circumstances, it gets bigger.