Ditto
The Cathedral Doors make it a Grandma III if there is no glass. The manual is in the sticky section at top. A damper should be installed in the first section of straight pipe within easy reach. It becomes your only control with a screen in place in Fireplace Mode. You will also find when kindling a fire with paper, cardboard and small branches, it will roar up the stack when first lit very easily. Closing the damper until the roar stops keeps the heat in the stove to ignite the larger kindling. You could slow it down closing the air intakes, but that slows the fire by depriving it of oxygen. You don't want to do that when first starting it. It needs all the oxygen it can get. Once up to temperature, you can control the rate of burn with the air intakes.
Your 8 inch flue requires a lot more heat than a 6 inch.
You should put a magnetic pipe thermometer on the single wall pipe just below where it goes into insulated chimney. In operation the stove top should be about twice the temp of the pipe. That means a 600* stove top may read about 300* to 350* at the base of chimney with controls set correctly. This is not actual flue temp, you would need a probe type thermometer which is even better and you would need that to try a heat reclaimer. Since the object is keeping the flue above 250* all the way up, you can only guess what the heat loss is all the way up. Checking the creosote formation regularly (weekly, monthly, etc...) until you know how much you create. When there's no smoke in the coal stage, temp doesn't matter, you can close damper to prolong the fire. Cold air blowing across the spark screen loads the screen up and plugs it first. Then the coolest part at the top will form creosote more than the bottom where it's hot. Once you know how much heat to leave up to keep it clean, (with damper or air intake and rate of burn) going by the thermometer as an indicator, you will know what temperature the pipe needs to be for clean burning. You will soon find where the thermometer runs mid burn, and if it's close to 300 or 350, you simply can't extract any more heat from the exhaust without going below the threshold of causing problems. You will find you simply don't have extra heat you can steal from the chimney. THEN if you must try a heat robbing device, try it. BUT you have to keep the pipe temperature the same or you will have problems clogging the screen and creosote near the top real quick. If you don't mind cleaning the chimney constantly, there is another reason you don't want one. Stove operation;
A fire will not get oxygen in a box without being connected to a chimney. The rising exhaust gasses are lighter than surrounding air and rise up the flue. The hotter the inside flue temp and colder the outside temp, the more temperature differential. That's what makes the stove work. That's why you have to consider the chimney being the engine that drives the stove. (In Georgia you're not going to get the temperature differential of up north. You have a weaker draft to start. Below zero outside a chimney and stove really starts to work better. Above 40 you have little and weak draft) Atmospheric air pressure, or the weight of air PUSHES into the stove intake to fill the void created by the rising gasses in the chimney. Cool the rising gasses, it becomes heavy, slows and doesn't allow oxygen into fire. Poor performing stove. It not only has to do with less air getting in, the velocity slows and air mixing with the burning gasses that come off the wood becomes dirty and creates poor combustion. The critical burn zone temp at flame tips drops, increasing smoke, stove temp drops, defeating the purpose of extracting more heat. That's the technical reasons you don't want one. You can see why the 250* flue temp is not just to prevent creosote. It is required for proper stove operation.
How many square feet are you trying to heat in Georgia that makes you think you need more BTU output?
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