cavemanmike said:
It's also important to note that you should have a flue liner and an insulated chimney or your stove will spend most of YOUR fuel heating the huge void in your chimney before it heats the room /house /cental heating. Don't want to sound obvious
Not sure thats true at all. The fire box gets hot, metal radiates heat out into the room. Any heat then left in flue gas as it goes up the flue, insulated or not, just goes up the flue, It doesn't somehow magically go back down and into the room.
However, you *should* insulate your flue, but for a different reason.
Its all about the flue temperature.
In order for a wood stove to work efficiently, it needs to be running at about 600 degree C.
Providing enough O2 is supplied to the stove, at this temperature, all the volatile fumes and char should be burnt off, leaving little in the way of particulates and flue gas comprising Nitrogen and its oxides, CO, CO2, and H20.
If incomplete combustion occurs due to lack of O2 or low temperatures, your flue/chimney ends up full of particulates/soot, Tar, Sulphur and Nitrogen oxides which will (if the temp is too low in the flue) mix with the H20 vapour to create Suphuric and Nitric Acid. Hmmm nice. Which will rot your nice expensive flue liner (this is also why dry seasoned logs should be burnt, to reduce the H20 element as much as possible).
So insulating your flue, will keep the flue gasses hotter and prevent cooling leading to nasties condensing on the lining.
Ideally, you should use a small 4" flue liner (for a small 5 or 8 kW stove) to keep the velocity of the flue gasses higher, ensuring they get up and out the top of your flue before cooling. However, building regs stupidly says its got to be 6 inches, for some unknown reason.
So I'm not sure I'd want to be trying to squeeze out the last of the heat from my flue gases with heat exchangers an the like, bit miss guided I think.