Having just returned from Christmas at the family cabin (a log cabin my parents, brothers, and I built 40 some years ago--I was five), I have a question about heating buildings from cold, really cold. I can see the advantage of rocket mass heaters for maintaining heat; my dad had to stoke the fire in the high-efficiency metal box stove several times each night. But what of heating the cabin at the beginning? Does a RMH radiate enough  to heat a 400 s.f. space in a reasonable time, say a few hours, when the temp is down in the low single digits (meaning the mass stored in the logs is also down there)? We start the Monarch wood-burning cook stove, open the flue to the oven, keep the oven door open, and stoke the heck out of it for several hours to get the place comfortable (meaning 50 degrees or so). We start the high-efficiency, too, but it doesn't do much to warm the place--its purpose is maintaining the temperature.

In practice, I expect this is a common issue for folks who are likely to build a RMH. For example, we have a friends in SLC, UT with a cabin up one of the canyons. They've said that in the winter, the husband heads up to the cabin several hours in advance of the rest of his family to start the fire. I guess what I'm saying is I want it all: I want a stove that heats a place relatively quickly and then maintains the heat.

There are two parts to this.

1:  heating a shop where you are going to leave the space and you don't care if it gets cold when you leave

2:  heating a cabin where you are going to stay for several days.   The fire will go out in the evening and you want to be warm in the morning


We have quite a few examples of #1.   And we have some examples of #2.  Your need is obviously the second one.

I think a standard J-tube rocket mass heater could be just the thing.   The barrel puts out quite a bit of heat.  For a 400 square foot structure, a six inch system should be plenty.   It will heat the space at about the same speed as the wood stove you have now, but it will continue to heat the space after the fire has gone out and your overall wood consumption would be much less. 

If you feel like "I want lots and lots and lots of heat, super duper fast, but just for right now", I see two different paths:

A:  Feed the system smaller wood much faster.   It will all burn hotter and faster until you move up to bigger wood.  This trick will also work on your conventional stove - but that thing will eat about ten times more wood to give you the same heat. 

B:  Install an 8 inch system so you can have faster heat when you need it. 

Hi Grant;  If you leave the majority of the 55 gal barrel uncobbed it will heat 400 squ ' as fast as the monarch will (just like an old 55 gal barrel stove would) , It will, take quite a while to get the mass up to temp .  In combination with your monarch, a RMH may replace that wood gobbler they call highly efficient . Good news is they both take the same size wood, AND you will burn A LOT Less!  Oh Yea , after  you get that mass heated up ...  no fire all night !!! 

paul wheaton wrote:There are two parts to this.



A:  Feed the system smaller wood much faster.   It will all burn hotter and faster until you move up to bigger wood.  This trick will also work on your conventional stove - but that thing will eat about ten times more wood to give you the same heat. 

Thanks, Paul. Your response is very helpful. Your A solution is essentially what we do with the two stove system. The Monarch stove has a small burn chamber and uses a lot of small wood. The high efficiency takes bigger wood and burns for a long time. But you're right, we go through a lot of wood even after we get the cabin heated.

I've not built my rocket stove systems yet, but have been researching them for some time.  I might be wrong, but you probably could have a bypass barrier that allows you to slide it in place to bypass the bench and go straight up the chimney for the first little bit, getting your barrel and chimney radiating a lot more of  the heat in the beginning, and then later switch the bypass so that they gasses heat the bench once you are close to comfort level in the room.  In my thinking, with a cold system, this would allow the for a very positive initial draw as well since the gasses stay hot and fast rather than giving off their heat winding around in the bench.   Maybe this is poor RMH practice?  I don't know.  

Excellent idea Roberto!  I would however , only use the bypass long enough to get the chimney heated up then switch into the mass. Otherwise the mass would be a great big refrigerator in the living room...  Grants monarch works exactly the same way,  run the flue open to start and as soon as possible pull the lever redirecting the heat around the oven.   Cold or a hot mass ,the uncobbed barrel should give off the same amount of heat, just want that chimney heated up to start the draw.    
(EDIT)   Just realized that  Matt Walkers tiny house cookstove heater could be your answer! 

My opinion, build a batch rocket. Like  this one

https://permies.com/t/71575/Casserole-Door-innovative-door-batch

But a smidge bigger i would say.

With a cast iron top , instead of  the arch.

Along the lines of Peter's double shoebox, or matt's riserless builds.

https://permies.com/t/71823/batch-core-riser


https://permies.com/t/72880/permaculture-projects/double-shoebox-rocket-cook-stove

https://permies.com/t/71700/Tiny-House-Cook-Stove-Heater