rocket mass... boiler?

First up, I know very little about rocket mass heaters - other than apparently they are super efficient, super low emissions, and use thermal mass to let you burn heat fast now but slowly radiate heat out over the next day or so.

What i'm wondering is to what degree (if at all) it's benefits could be applied to a boiler...


I want to have heat in a number of different places (normal house, greenhouse, workshop, sauna, eventually a year round swimming pool) and building multiple separate daily fires for a few extra % efficiency seems like both a hassle and possibly a safety issue (I have a thing about unattended anything - if it's in the same room where i'm physically present at least i'm there to keep an eye on it).  I was currently planning to use some kind of boiler and piping steam or hot water to the different locations.

Would an RMH still have a purpose in these situations?  Sell me.  

Rocket heaters are clean burning and efficient.
That is reason enough to consider them as a way to heat the water in a hydronic system.
They burn clean and hot and the heat is stored in the mass.

Conventional wood boilers burn dirty.
They could burn cleaner, but the systems are designed to shut off combustion air and smolder when heat isn't needed.

The most strait forward way to create a clean burning solid fuel hydronic system is to add a huge insulated buffer tank  or tanks to an conventional system.
If you have the money, it may be the best way to go.
If you are going to build your own system anyway, rocket heaters are both diy friendly and efficient.

A rocket boiler would also need a large insulated buffer tank or you can embed a heat exchanger in a solid thermal mass,and insulate the outside of that.

Many of us have reasons we won't build/use a homemade heater inside our homes.
An advantage of a rocket boiler is the ability to locate it outside of the structure you are heating.

In my greenhouse, have built a TLUD powered, charcoal producing boiler from a water heater tank.
My buffer tanks will be a series of other water heater tanks.
Heat distribution will be via bottom watered sub irrigated planters.

I do think i'd like the idea of just building ONE fire per day and have it finish whatever it's doing under supervision and then not worrying about it until next midday or whenever i'm well up and ready to want to deal with it.

I'd have some efficiency loss by not directly heating the space i'm aware - I think once you start talking about multiple areas (3+) that need heat that's a fair tradeoff despite losing some efficiency.

Hopefully I could gain some efficiency back if adding some solar water preheating or something...

My guess would be I just build a big thermal mass for the rocket heater but have piping inside it and use the water to extract the heat from there.  Also only one thermal mass to insulate instead of multiple/I might lose individual efficiency per-stove but could gain some back having one single monolith to heat, maybe even last more than a day of heat depending how set up.  Was trying to think if my needs for heat 'scale' should I have more than one boiler or mass, but in reality it might just be "build a big 'un!" and heat up the whole mass in one blazing fire, then tap that thermal mass with the water piping whether it lasts for 1 or 5 days at the level of btu drawdown I need.  If I have an energy emergency and have to prioritize heating the house over something like a recreational pool just turn some valves i'd think...

Any reason this shouldnt work?  Have people built rocket stoves that hold heat for beyond a 24 hour cycle much?

I love this idea.  I proposed something similar a while back.  

I'd suggest replacing the word "boiler" with something else.  In this case I suspect you would be just trying to get water hot (180F?).  When it boils, bad things happen.

I could imagine a huge insulated water mass (1000 gallons?) heated by a big batch box rocket.  The batch box core, riser and barrel could almost be inside the water tank.  Maybe there'd be a way to have a hot exhaust gas escape route on a thermostat so if the temp of the water gets above 190 it opens and the heat escapes without overheating the water.