Smoke from chimney problem with Tarm 140

[jfrog]

Hi - I am brand new here so please forgive me if I am posting in the wrong category--

We have just installed a tarm 140 and we have smoke coming from the chimney which I know is not supposed to happen. The doors appear to be closing tightly, the seals are good. We took off the front panel and doors, resealed both doors. Behind the door and sheet metal, there were no good seals. Have a good burn, but when it shuts down we get smoke out of the chimney. Is it possible that there could be too much draw on the chimney? I also checked the bypass door and it is opening and closing properly and working freely. We have an 8 inch flue. Please let me know if there is any more information needed. Thanks in advance!!

I should add that we are burning well seasoned, dry wood.

 

[Nofossil]

Welcome to the boiler room....

I don't know the Tarm specifically, but if that model is a gasifier I'll assume it's similar in behavior to others.

When you say 'shut down', do you mean when the blower shuts off due to lack of deamnd for heat? If that's the case, then I'd suggest building smaller fires to see if that helps. During the first part of a burn, there's a LOT of pretty noxious woodgas that's generated in the primary chamber. If the fan shuts down, woodgas production does not stop immediately, and that could explain what you're seeing. A chimney with enough draft to be useful will pull some air through and could create what you're seeing.

In the latter part of a burn, you''re just burning charcoal, and idling at that point is pretty clean.

 

[jebatty]

Behind the door and sheet metal, there were no good seals.

The install manual for my Tarm instructed to add the provided sealant where you indicate. A good layer between the metal shell and the boiler itself and another good layer between the doors and the metal shell.

Have a good burn, but when it shuts down we get smoke out of the chimney. Is it possible that there could be too much draw on the chimney?

If by good burn you mean good gasification (assumed secondary air control about midpoint) until draft fan shuts off (boiler temp about 190), then smoke out of chimney, some smoke is normal as primary fire dies down. What is your flue temp during idle period? Does it steadily drop from gasification burn (400-600 is my range; Tarm told me that about 600 is average) to 100-200? If not and temperature is much higher, you may be getting chimney air draw through draft fan damper opening or other air leak into firebox to maintain a low burn. It takes a few minutes for flue temp to drop to 100 or so. Adjust the draft fan damper to maintain proper gasification burn flue temp, and if no other air leaks, at this point I don't know what to suggest if smoke continues during idle period.

You also will get smoke on start-up after idle until gasification re-starts. Nothing you can do about this.

How dry is your wood? Wood must be dry (20% or so), not green. If your wood is wet, you may be getting smoke from inefficient burns.

What sizes are your splits? Tarm recommends 4-6". If you are burning very large chunks, there may be insufficient surface area to get efficient burns with smoke as a result. I do burn some larger pieces but the bulk of my splits are in the recommended range.

Are you getting "bridging" during the burn? This is evidenced by an interruption in gasification (take a look through the view port). Search bridging on this forum to see what I mean. You will get smoke, maybe a lot, during a bridge and until the bridge collapses and gasification restarts. A search on bridging will provide ideas on how to minimize bridge events.

I have a 6" chimney flue with very good draw. I really had to damper down the draft fan to get flue temp into the 400-600 range, and still with my very dry, pine wood flue temp will rise above this during the early and very hot part of the burn. The bulk of the burn will be in the 400-500 range.

Continue to experiment. There is a learning curve to find that sweet spot of operation. Might be a bit frustrating at first, but as you move to the sweet spot, the end result will be very satisfying. I rate my satsifaction after one full season and now into the second season of operation to be 95+% -- met and exceeded all expecations.

 

[jfrog]

Thank you so much for your responses!! I have printed them out for my husband and will post again once he reads through them. We did add a barometric damper a few days ago and that has help a lot with the chimney smoke. Thank you again-this is an absolute GREAT place to come for information!!

 

[jebatty]

I would encourage you to attempt to solve the smoke problem without using the barometric damper, although sometimes it is the only possible solution. A barometric damper has its own set of issues.