RMH or masonry stove refurbishment

Hi Permies friends,

You dont know this, but i have been following you for a while. Me and my girlfriend have recently bought a 180 Square meter house. One of the Things that we loved about the house was this old fireplace insert. I think it dates back to the 60s. It is huge, so we hardly ever fill it to more than a quarter of the volume. It already functions somewhat like a masonry heater with all the mass around it(see Picture one) because if we have had a fire going in it the day before it is still warm the day after. It still seems like we should be able to get more heat out of the wood we burn.

We would like to convert it, to become a little more efficient. My thoughts are:

1) to build a baffle inside of Firestone to bring the fire to the front of the firebox and increase the temperature of the combustion. I am considering to also reroute the primary air in a channel inside the firebox to wash Down the glass and therefore reduce the risk of sod.

2) The second upgrade would be to create a tunnel system for the chimney to have the hot smoke stay inside the chimney longer, and therefore increase the heat output. As you can see in the last Picture, there is quite a bit of Space above the fireplace insert, so i was thinking to make a diversion of the smoke and bring it up and Down in a rocket mass heater style bell. do you all think that would Work? My concern is that i have not seen anyone combining an ordinary fireplace with a masonry heater/RHM tunnel system chimney.

So please send me your ideas (and let me know if you need more information.

Anders

Without a rocket core that burns the fuel completely and efficiently, channels to extract more heat will let creosote deposit inside. Ordinary woodburning appliances are required to have high-temperature exhaust (min. 350F in the chimney) to avoid this problem.

So to make your conversion, you would need to clear out the fireplace interior and build a rocket core, either J-tube or batch box. Then we can talk about how the gases are encouraged to give up more heat to the mass.

Hi Glenn,

thanks for the answer I can fully understand that a completely clean combustion must happen when using a 'tunnel like' exhaust for the smoke. But a lightweight baffle system with loads of air would quickly become very hot right? I was thinking of using it as a batch box, but with smaller batches (say 10 pounds) of wood. The volume inside the current firebox is approximately 100 x 80 x 65 cm. So there should be plenty of room to make a batch box inside. Or am I completely of track here?

It's not so much the character of the channels that are absorbing heat as the fact that the heat is being absorbed. Unless you have a rocket type of clean burn, you will have creosote that must be kept hot enough to not condense until after it is out of the chimney.

It does sound like you have enough space to make a 6" batch box, especially if you go with one of the newer "riserless" styles, like this:
http://walkerstoves.com/walker-riser-less-combustion-core.html
http://donkey32.proboards.com/thread/1690/walker-core-variation