Secondary burn attempts. HotBlast 1557

[Drummerking55]

Hey. New to the forum and to wood burning. I installed a HotBlast 1557 in the basement of our old farmhouse. 24 feet of stainless steal lined chimney. I drilled a 1 inch hole just under the smoke shelf in the back and welded in a pipe for secondary burn air. The pipe comes in the back and t’s off to 2 pipes that go out to the outer edge of the stove up to the front then in a little then back down the length of the firebox all just under the smoke shelf the pipes as they make 2nd run down the stove have 7/32 holes every inch to let air to the top of the fire after it’s preheated . I am having trouble keeping the secondary burn going. I get the fire roaring then shut the bottom ash door leaving the spinner almost closed. Damper on top full open. The secondary burn starts and will go until the fire underneath dies from lack of air. Then the secondary dies and I’m left with a smoky smoldering fire. If I open up the spinner some I can get the secondary’s to stay lit but goes through wood. Full load of dry walnut gone in 5 to 6 hours. I do have firebrick on top of the smoke shelf and some added on the back. Any tips on settings to keep the secondary burn going while dialing back the main burn. I will add pics in the am.

 

[RockyMtnGriz]

I've thought about trying what you're doing, and because I thought I'd get tired of tinkering with it before I got it to work, I've always passed. From watching secondary combustion stoves work, I think there's a lot of things that have to come together to make it work. Firebox size, insulation, gas flow paths, secondary air flow and temperature, I'm going to think are all variables. A lot of welding, grinding out, rewelding, drilling, re-drilling... to get it to work.

But, I admire your courage!!

Just thoughts:

You need to keep it hot enough for secondary combustion - somehow. If it falls apart when you turn it down, this is probably an issue. It already sounds like your firebox might be too large or tall, and/or not concentrating the hot gases so they flow across the top and mix with secondary air.​

​

Any secondary air that doesn't get used, is hurting you by carrying heat up the chimney.​

​

I had a furnace similar to that, and 6 hours would be good. With enough strategy in loading, I could get 8 hours - but unreliably. No way I could have the kind of fire that would have been efficient and get close to 6 hours, but I don't have hardwood.​

​

There's going to be a limit to how much you can turn down a stove and get secondary combustion. If you have a big firebox, or a counterproductive design, that's going to move the limit up.​

​

There's a reason that many of the stove companies that existed before efficient combustion was a requirement aren't around anymore. If it was just a matter of adding some air tubes, they'd still be selling stoves.​

There's a thread over on the Arboristsite about this exact project, I think. Multi-year fiddling was involved. You might get some ideas from that one though, since I think it's the same stove they're talking about.

 

[FixedGearFlyer]

I once modified our old Vogelzang Norseman for secondary burn. It worked, but I had to plan for preheating and metering the secondary combustion air, metering the primary air, insulating the firebox and baffle to hold high enough temps for secondaries, and plan the gas flow from back to front so that it was *just* right and supported secondary combustion rather than snuffing it out.

In the end, the higher temps and slower gas movement in the furnace killed it and probably wasn't safe, at all.

We switched to an EPA furnace with secondary technology (a Drolet Tundra) and it is infintely better, with much greater control, higher heat exchange, and better efficiency.

I'm not trying to discourage you (heck, I did it, too!), but if I had it to do over again, I would save two years of tinkering for marginal results and just invest in a better furnace to start with.

 

[brenndatomu]

I think there's a lot of things that have to come together to make it work. Firebox size, insulation, gas flow paths, secondary air flow and temperature, I'm going to think are all variables. A lot of welding, grinding out, rewelding, drilling, re-drilling... to get it to work.

Totally agree...its not as easy as it seems...I tried it too, it worked, sorta...made the furnace cantankerous to run and it would back puff sometimes...I moved on to a model with factory tubes...which turned out to be a wise choice.

 

[Drummerking55]

Thank you for the input. I will eventually upgrade but thought I would try this for a year or 2 as right now it’s what my wallet can handle. I achieved better results by rearranging and adding some more fire brick over the smoke shelf. And switching the wood I was burning. From sort of seasoned black walnut to pretty well seasoned cherry. What a huge difference. 10 hour burn and I did not fill the stove all the way. Also the stove seemed to kick into secondary burn because it was putting off a lot of heat but the flu temp never exceeded 250. I’ll continue to tinker to get it dialed in. I did Include a valve on the tubes so I can meter air. And the gas although I did not plan it this way does seem to travel from back to front of the stove. Anyone have a favorite wood to burn? If so why.

 

[brenndatomu]

I wondered if your wood wasn't quite dry.

seemed to kick into secondary burn because it was putting off a lot of heat but the flu temp never exceeded 250

Yup.

Anyone have a favorite wood to burn? If so why.

I like lots of different woods for different reasons and different parts of the winter.
Many people turn their noses up at Silver Maple, but I like it...drys pretty fast and burns great...and it off gasses hard, so the secondary burn is killer. I like to mix a few pieces into a load with other wood species...burns great.

 

[maple1]

All I can say is be very very careful. A good secondary burn can generate way more heat than those things were designed for.