Masonry Heaters

[tljones]

Evening all,

I am wonderin if any of you have any knowledge of or experiance with Masonry Heaters, aka Russian or Finnish heaters.

I have been reading about them for years, and have been able to find many answers  to many questions. But one has come up that is really giving me a headache, and I thought someone else might have some insight if I could bounce it off there heads.

These heaters use small fireboxes often found in series to gasify wood and burn with very high efficiency. The exhaust gases are then routed through the large mass of masonry in a downward direction (they are also known as contraflow heaters). It is this long path through the masonry before going to the flue in conjunction with the hot fire that gives such high efficiency. It appears that generally these are formed on a slab with an ash cleanout below.

My home is a two story ranch on a walkout basement. Our main living area is on the upper floor, with utilities, storage, kids rooms and a small den in the basement. The designs that I have been able to find with the heater on the second floor usually include a simple cement block column with a large concrete pad on the top upon which the heater is constructed. Often the slab is pierced by a hole allowing ashes to be dumped into the block column as a long term dump. When you get to the heater, the firebox sends its gases upwards into a channel which splits and flows downwards almost to the slab then back upwards to exit the top of the structure into the chimney. Sometimes they have long horizontal runs that serve to warm masonry benches or a chamber that works as a stone oven. Before someone asks the question, these firechambers are designed to burn very hot, so little creasote is created, although any channel has access built in for cleaning them.

My question is this. I want the fire upstairs, by my deck doors for easy access and in the living room where we spend our time. But I also want a lot of the heat downstairs. So instead of building on a slab, why could I not build the entire heater two stories high with the firebox in the upstairs, and the contraflow channels running downwards for 15 feet instead of five. This would dramatically lengthen the total lentgh of the heat exchanger, and give me one hell of an efficient heater I would think. I could insulate and isolate the portion penetrating through the floor, and since my floor is made of web trusses instead of I beams I could tie them into the structure as well.

Has anyone seen a design like this, or do you have any thoughts??? I would incorporate a water heating coil in as well..... maybe in the area of floor penetration. That would serve to cool that portion very well, and help keep heat away from the floor.

Thanks in advance for any thoughts,

http://mha-net.org/

Tom

[Stonebrain]

I have build a small masonry heat accumulator.

It's constituted of about 120 special firebricks,maybe 300kg total.

Maybe I'll post pics and more details someday,if people are interested.

I have quality scandinavian stove that burns with very little creosote.

The accumulator is heated withh the exhaust gasses of the stove.

It works for more than 4 years now and I'm satisfied ,sure the accumulator can last longer than the stove.

The smoke goes down for about 1,5' before going upward again.

My estimations are the stove dissipates more than half of the heat,the accumulator half of the remaining heat and the 3m iron pipe after the accumulator a significant proportion of the heat still in the gasses after the accumulator.

It can be that the efficiency is around 80%.

Probably with an heatexchanger for water in theory I can get over 90%.

But you have to be carefull not to go to far

If you get excessive condensation you know you want too much.(Maybe above 85% or90%?).

This condensation is very corrosive and will destroy any iron parts(except stainless) and penetrate in masonry.

Worse, you can create situations where co (carbonmonoxide) will be dissipated,which is extremely dangerous.

For the downward part of the flow through the masonry I have to give the same kind of warning.5' is quite a lot allready.And I would never take the risk to go down ffor more then that.The first,downwards part of the channel is the hottest and this effect in a draft in the wrong direction.There can be a point where the drafft in the upward channels is not enough to counterbalance it(of course this depends on the length and t°of the upward channel).And a bad working stove is allways dangerous,mainly for the co.I would rather say 3 or 4' is enough,keep it on the safe side and forget about the 15' downward channel.If you want too much you will have to pay it back,possibly even with your or someone elses life.

My accumulator is just an improvement of my stove,boosting the effficiency and spreading the heatdissipation.

In my case 300kg masonry is enough to handle 1/4 of the heat ffor my 8 kw rated iron cast stove.

To handle all of the heat from a 10 kw fire in masonry you need probably 1500-2000 kg masonry.

There is a drawback from the 100% masonry approach:when you light the fire it's a long time before it really starts heating.I love the idea though.

Just my thoughts,

cheers,

stonebrain

 

[chadking]

Hello:

If you get a chance to take some, I would appreciate some pictures. If not, that is ok too. I have read many times about large, heavy masonry stoves holding heat for extended periods of time. But I have been unable to get any real details on them.  

Like you, I understand that they have pro's and con's...but the concept is very intriguing. Congratulations on actually completing one!

[skipinder]

Hi there tljones, I too have been reading all about these amazing yet simple stoves, you've probably seen their pages already, but here's a link to a similar project on the masonry heaters association page...

One day I hope to build my own...

http://mha-net.org/msb/docs/c-smit.htm

[spinningmagnets]

Here's a great link to add to this thread, good graphics and pics of actual units.

http://www.lowtechmagazine.com/2008/12/tile-stoves.html