underfloor flue temperatures

[donaldl]

Hi folks;New to this forum.Began following J. Sieganthaler's wood to water series and he recommended this forum.I plan on building a underfloor masonry heater and flue(also known as a Kang or Ondol) system.I want to use it as supplemental heat to our geothermal/radiant system.
The firebox and flue will be firebrick and high temp. castable refractory.Firebox will be 30 x30 inches with 2 /9 foot x 12x12 inch flue runs.I want to mount a simple black pipe water manifold above the castable refractory flue runs(isolated from the smoke chamber) to gather heat.(hopefully limited to 150 degrees).I prefer to keep the temperatures low
Does anyone have experience with this type of system?What I would like to know specifically is what flue temperatures can I expect from an underfloor system like this after one firing?Thanks,Don L.

 

[DaveBP]

I remember reading a long article about the traditional Korean use of these systems. The Romans did it as well.

I think the key to using the actual wood fire exhaust to heat the floor is that they are run through the soil beneath the floor. The high mass of the soil absorbs the high heat and releases it slowly at a lower temperature. Are you talking about putting this beneath a concrete slab?

 

[donaldl]

Dave;Thank you for your response.This system will be inside the building envelope.It will be built under a raised 30 inch foyer entering our great room.The firebox and horizontal flue runs will be placed on a 4 inch concrete slab lined with fire brick.If I can determine the average temperature of that 3x10 foot area of the flue runs I can better determine whether our heat exchanger should be directly above the flue and oriented horizontaly or place it vertically adjacent to my flue runs.As stated, we want to limit the heat transfer to 150 degrees or less,for safety reasons.Thanks,Don L.