Tarm boiler, blow back from draft controller

[Nathan Babb]

I have a combi Tarm boiler. We recently had a new stainless steel liner installed, and I've noticed on occasion that when the boiler is firing there is this cyclic blowback through the draft controller. You can hear the buildup and then there's a burst of air/smoke that comes out through the draft controller. It seems to settle down once the flue heat up, but in the meantime the basement fills up with smoke. It's a six inch in diameter liner, high quality stainless steel. It does have one of those caps on the top. I'm wondering if that might be impeding the draft?

If anyone has some insight into my problem I'd really appreciate it. I'm uploading a video to YouTube and will post that shortly.

Thanks

 

[Nathan Babb]

Here is a link to a video showing the problem.

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[LarryD]

Holy Crap!

What are the stack temps? Quality (how dry) of the wood? What is your air setting?

 

[Nathan Babb]

The stack temp starts out low and ends up in the 300-400 range. It does settle down eventually. The wood is nicely seasoned, so dry. I leave the air setting in the middle...

 

[LarryD]

You say "The stack temp starts out low and ends up in the 300-400 range. It does settle down eventually." What temps do you let the stack get to prior to engaging the damper on a "cold" start?

LD

 

[kopeck]

Take what I'm going to say with a grain of salt because I don't know what I'm talking about but I don't think it's wood issue.

That seems like some weird draft issue.

This is happening when the blower is going? Does your boiler have a bypass?

K

 

[BoilerMan]

Is the smoke just coming out of the barometric damper during this event? Or out of other places on the boiler as well? How does it do on oil? What does the smoke look like outside at the top of the chimney when this is happening?

TS

 

[goosegunner]

My Econoburn will do the same thing at times. Cold start wit a large load of dry wood. I think it is caused by too much fuel for the nozzle to ignight. I have only had it happen on cold start.

I installed a stainless screen over the damper to catch anything that could possibly come out.

gg

 

[Nathan Babb]

You say "The stack temp starts out low and ends up in the 300-400 range. It does settle down eventually." What temps do you let the stack get to prior to engaging the damper on a "cold" start?

LD

We had a fire going in the fireplace upstairs, so I think maybe the boiler had been idle for some time but with a decent amount of wood still in the box. So when the boiler did kick on the stack was probably on the cold side. The other time I saw this happening was during a cold start when I was first getting the boiler going. I don't recall this happening though when I had a clay liner in place. That liner cracked recently so we had it replaced with a stainless steel one.

 

[Nathan Babb]

You say "The stack temp starts out low and ends up in the 300-400 range. It does settle down eventually." What temps do you let the stack get to prior to engaging the damper on a "cold" start?

LD

I usually don't even look at the stack temp before engaging the bypass damper. I usually base it on time, say 5 minutes, to let the fire get going. I imagine the problem would go away if I keep the damper open and let the flue heat up enough. I'm still wondering if there's an issue though with draft. In this most recent situation the boiler had been "on" for awhile but had probably been idle long enough for the chimney to cool down (we had a fire going in the fireplace upstairs that was doing a lot of the heating, so the boiler wasn't calling for heat).

 

[Nathan Babb]

Is the smoke just coming out of the barometric damper during this event? Or out of other places on the boiler as well? How does it do on oil? What does the smoke look like outside at the top of the chimney when this is happening?

TS

Yes, smoke just out of the damper, no smoke from other places. Not sure about with oil, I haven't noticed the problem when we've been on oil. It was nightime during this latest event, so not sure about the smoke at the top of the chimney.

 

[Nathan Babb]

Take what I'm going to say with a grain of salt because I don't know what I'm talking about but I don't think it's wood issue.

That seems like some weird draft issue.

This is happening when the blower is going? Does your boiler have a bypass?

K

Yes, when the blower is on and the bypass is closed. When I open the bypass the problem goes away.

 

[goosegunner]

Yes, when the blower is on and the bypass is closed. When I open the bypass the problem goes away.

I would guess that you have smoke from the stack also, Boiler is not burning all the fuel.

gg

 

[taxidermist]

I think you are getting smoke explosions try and let the fire get going a little more before you close the bypass. Mine will sometimes do that if I try to rush the fire..

 

[rkusek]

Looks like what I call "huffing & puffing". Too much fuel for the nozzle to burn at once like the guys above said. I think the wood can be a factor as well as other things. Lots of small splits that are very dry might work better mixed with some larger not as dry pieces. Does the Tarm have adjustable fan speed? I used to run mine at 70% to reduce the BTU output and give me longer burn times w/o idling but I went back to full 100% speed this year after I caught it doing the H&Ping mid burn on a milder day. Running at full speed seems to prevent this condition based on my experience anyway. You also mention this happens coming out of idle. Does the Tarm have settings for that periodic burst of air at idle? Don't remember what mine is set at but it's like a 10 second burst of fan every 5 minutes when it is at idle. That might help keep the wood gas from building up at idle. Your cold startup process may or may not contribute as well. I never run mine with the bypass open and a full load of wood in the box which starts burning the whole load prematurely IMHO. Usually just a couple splits on top of some kindling over the nozzle with the lower door open and fan off. I let this run for a good 10" heating the flue and producing some red hot coals while I re-stock my wood supply from the pile. Then I close the lower door, load it to the top quickly, close top door, close bypass, and start the fan. The pictures of downdraft gassers like ours in action alway show the wood burning from the bottom up. A hot bed of coals at the nozzle with the fan pulling air downward extracting wood gas out of the load igniting it at the nozzle. I know others here seem to have good luck loading their boilers differently so I would like to point that out as well.

 

[LarryD]

We had a fire going in the fireplace upstairs, so I think maybe the boiler had been idle for some time but with a decent amount of wood still in the box. So when the boiler did kick on the stack was probably on the cold side. This does seem like a cold chimney/draft issue. I have seen a similiar issue with my boiler (not to the degree in your video!) and I experienced it after some idleing. I have storage, so I have no experience with frequebt idling. You may want to adjust how much wood you load it with under "low" heat load situations. Obviously the more wood=more wood gas. More wood gas+idleing=more creosote and possibly the "huffing and puffing"
The other time I saw this happening was during a cold start when I was first getting the boiler going. I don't recall this happening though when I had a clay liner in place. That liner cracked recently so we had it replaced with a stainless steel one. How long ago was the liner installed? Is this a part of the learning curve? I imagine this will change how you might normally "run" your boiler. The liner may cool off quicker than the clay chimney. Try paying attention to the stack temps. The thermometer is like the speedometer. I try to see 400* before I close the damper. This works well for my set up.

Let us know how you make out.

LD