and there is always something new to learn. There are also REGULATIONS that interfere with efficiency because of safety.
First, the maintenance of the stack
Second, the quality of the heater
Third, the quality of the wood
Fourth, the methods of heat extraction
Fifth, the operator
Sixth?
I noticed there was an Alaskan commenting on the stack robber (Magickheat, Heatolater, etc). Having burned wood that was soaked in seawater in SEAlaska and had a roaring stack fire on the third story of a mountainside home in Ketchikan (with a stack robber) in the middle of an ice storm. I could comment on that!
So, I asked around when I lived on Orcas Island in Washington, about the stack robber with an airtight stove and they said no problem! This time on a 2 story house with a humongous stack fire in a double sheet-rocked plennum surrounding the stack!
So here is my answer:
!. Shortest verticle stack possible with ease of cleaning the priority!
- Twice a year during the burning season I clean the stack (or more often if I've smudged the fire).
- I burn superdried wood only.
By now you probably wonder "What happened to the heat efficiency we were asking about?".......I'm getting to that!
My current heater is an Irish Ashling from Waterford. I asked an expert about using a stack robber with this stove: "If there ever was a creosote generator it would be an Ashling with a stack robber!" was the reply and it is against the law to do that in Washington State!
So, just last month after two years of the Ashling's operation and the Magickheat sitting in the garage I put the Magickheat in line for a trial. We had been sending, maybe 1/3 to 1/2 of the heat up the stack! The Magicheat runs 100% of the time if the heater is properly managed and there is no discernable accumulation of soot/creosote on the stackrobber scraper. The Ashling has the auxiliary squirrelcage fan to blow air over all that cast Iron. It ran half the time over the previous two years and still does.
In Yosemite National Park I saw my first horozontal run of stack...amazing...it ran the length of the building just over our heads and it was doing a toasty job. I don't know how often they cleaned it (it was sure to be a nasty job) and I don't think they ever stopped the fire during the winter. Maybe the place burned down....
Now-a-days it goes like this. If you want to play the insurance game, and don't know what you are doing with a wood heater, follow the regulations. If you have some knowledge of woodburners, operate your stove for high efficiency, and train others to do it properly when you are away it should be ok. They might not/probably won't or some stage in between, so CLEAN THAT STACK more often than necessary for their sake. And yes, I've been known to "smudge my heater" to extend the burn. It's all a compromise.
You should be impressed witnessing a stack fire. I haven't seen what one would do to triple wall stainless but I won't ever witness another stackfire in my home! Single thickness pipe radiates alot of heat and may be illegal, so there goes more heat up the chimney with double or triple wall.
Finally, smaller stoves concentrate the heat so that stack and even the stove can get cherry red.....enjoy!