Installing heat exchanger in fireplace

[canuckinczech]

first time I have posted on this forum...I am really excited about finding it!

I have a 300year old bread oven , and have been slowly adding components to improve its efficiency. The chimneys stack is 50x50cm inside ,solid brick and is centrally located (for those of you building new houses...sacrify the space and go for a exposed central stack!). I put in 3 big birch logs a day and the stack accumulates so much heat it radiates and continually heats the whole house all through the next day!

I experimented routing convection tubes to individual rooms, however the measureable heated air transfer, turned out not to be worth the effort.

The current project is installing a coil/drum hot water heat exchanger...I had an old electric boiler w/ coil sitting around, so am just in the process of plumbing it in. The problem I am having is that I can only get enough hight on the boiler for the top of the coil/drum in the fireplace to be level with the top of the coil inside the boiler..."Is that enough to allow for thermal siphoning?" or does the boiler coil have to be significantly above the top of the coil inside the fireplace? I am not to keen on adding an electric pump to the circuit Crying or Very sad

I have been told that copper coil in the fireplace can't make direct contact with the open flame. Several people adviced me to buy a "drum(?)" insert with 2 ports on it which just sits in the rear of the oven/fireplace...since I have an allergy against buying things, I'd rather just build a thin high fired brick wall between the coil and the fire inside the oven...not sure which would be more efficient for circulation?

 

[edthedawg]

This sounds truly fascinating. Where are you planning to put the coil inside the oven? You will want elevation between the coils for it to siphon on its own. Can't tell you exactly how much elevation your setup would need. From what I gather at http://en.wikipedia.org/wiki/Thermosiphon it seems you'd be fine the other way around, with the heat source (oven coil) at the high point, provided you are essentially making a closed-loop heat exchanger, purge it properly, and ensure the system is routed without any high or low spots between the high point and low point...

Also can't tell you for sure what would do a decent job protecting the copper coil inside the oven, but I'd venture to say that anything one finds in the construction of any existing woodstove (cast iron, steel plate, firebrick, soapstone...) would likely be a good candidate.

Good luck and send more pix of this monster

 

[Fred61]

Old cast iron radiators make great coils. They come in all sizes and can be purchased cheap.