Drolet heatmax11 “explosions”!!

[nellraq]

In to my second winter with the heatmax. The install is textbook. inside stainless chimney – – about 25 feet long – – 2 45° elbows from the furnace into the chimney. Barometric damper installed Close to the furnace--just after the first 45. Connecting pipe is double wall stainless.
Dwyer manometer installed and set to .05...works well
chimney was cleaned before using the furnace in early October. Top of the chimney had a little creosote – – very little fluffy residue in the chimney – – connecter pipe had a little more but not too bad.
Burning Douglasfir that was processed about eight years ago and has been covered the whole time. it is very dry.
Have burned about 1 1/2 cords so far this winter.

now, finally, to my question/problem! once a new fire is going, I don’t open the door until re-loading time.
sometimes, I get a little smoke smell in the house. I think it’s coming from the damper, but I have never actually seen it... until yesterday. I came in to the house to find very very strong smoke smell.
The fire had burned down quite well with lots of wood left...all of it red hot...with little to no flame.

I watched it for a little while, and saw a small puff of smoke come out of the damper--followed by, a few seconds later an “explosion” which blew a lot of smoke out of the damper. it came about 3 feet into the room. It was followed by another explosion in the firebox which sent a bunch of smoke out of the front draft mechanism.
I know that this situation is caused by unburned gases in the firebox, but why wouldn’t the afterburner tubes take care of this??

I have since cleaned the stove out – – there wasn’t much debris in the heat exchangers. It could be that the chimney is partially plugged, but I highly doubt that.
Anybody out there have the same problem?? Any ideas re-. Re-things I could do to stop this from happening again?? it was a pretty scary situation, Which I never want repeated.
sorry for the length of this, but I was trying to include as much info as I could so that we can get the problem cleared up ASAP

 

[FixedGearFlyer]

You're right on - it happens when the furnace has lots of smoke or unburned gasses that suddenly hit combustion temp/air mixture.

You can avoid it by opening the damper sooner to avoid smoldering once you've lost secondary combustion.

 

[Wood1Dennis]

Is it possible that your home is tightly built and there is a negetive air pressure that the furnace draft cannot overcome? Maybe a power vent water heater, dryer, range hood, something like that? Our house is pretty tight, and usually is OK, but I have learned that if I use the range hood at somthing higher than low speed I have to crack a window or I might draw smoke in.

 

[Bad LP]

My Tarm boiler was doing it as well. Caped off the damper as a test and problem solved.

 

[nellraq]

My Tarm boiler was doing it as well. Caped off the damper as a test and problem solved.

I started off without the damper. Could not control the fire--it burned really fast and didn’t heat the air.Put the barometric damper in – – problem solved.

 

[nellraq]

You're right on - it happens when the furnace has lots of smoke or unburned gasses that suddenly hit combustion temp/air mixture.

You can avoid it by opening the damper sooner to avoid smoldering once you've lost secondary combustion.

Good idea, except I’m not usually home to open the damper at the right time. Wish I was more mechanicallyInclined. I would put in some sort of control damper that I could set.

 

[nellraq]

Is it possible that your home is tightly built and there is a negetive air pressure that the furnace draft cannot overcome? Maybe a power vent water heater, dryer, range hood, something like that? Our house is pretty tight, and usually is OK, but I have learned that if I use the range hood at somthing higher than low speed I have to crack a window or I might draw smoke in.

 

[nellraq]

house is mid 70’ build...pretty leaky! I always have a basement window cracked open..About 10 feet front the furnace

 

[Wood1Dennis]

OK, that's not it then. Just an idea.

 

[trx250r87]

Try adding a small nail, paperclip or electrical wire type staple to the front flap so that when it closes it remains open about 1/8"-3/16".

The "all or nothing" function of that furnaces damper is difficult to get dialed in.

Eric

 

[NaturalCauses]

Try adding a small nail, paperclip or electrical wire type staple to the front flap so that when it closes it remains open about 1/8"-3/16".

The "all or nothing" function of that furnaces damper is difficult to get dialed in.

This is what I've been doing with my Caddy furnace ever since I had my first puffback earlier this season. The nice thing about a paper clip is if you hook it around the damper you can adjust it up and down to better 'fine tune' the amount of air being let in, and it will stay in place.

 

[trx250r87]

This is what I've been doing with my Caddy furnace ever since I had my first puffback earlier this season. The nice thing about a paper clip is if you hook it around the damper you can adjust it up and down to better 'fine tune' the amount of air being let in, and it will stay in place.

I had one of the earlier Tundra's. SBI had an update kit that included a piece of sheet metal that got installed under the front damper flap. This piece changed the amount of primary and secondary air that entered the furnace when that damper was open.
Maybe call SBI and ask if that update applies to your serial #.

Eric

 

[brenndatomu]

Try adding a small nail, paperclip or electrical wire type staple to the front flap so that when it closes it remains open about 1/8"-3/16".

This ^ ^ ^...only not 1/8"-3/16"...that's too much. Start out with a paper clip, that will usually do the job. Small increases in diameter/opening can make a big difference. If you prop it open too much, things can get really hot at the peak of the burn!

SBI had an update kit that included a piece of sheet metal that got installed under the front damper flap. This piece changed the amount of primary and secondary air that entered the furnace when that damper was open.

That was just restricting the primary air a little...secondary air intake(s) was left alone.
That update was just for the T1...might not hurt to call them to check for other updates though...

 

[brenndatomu]

By the way, this issue is often exacerbated by wood that is not as dry as it could be...not saying its wet, just that its probably not crispy dry either.

 

[brenndatomu]

Good idea, except I’m not usually home to open the damper at the right time. Wish I was more mechanically Inclined. I would put in some sort of control damper that I could set.

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[nellraq]

Here ya go...

Everything Drolet Tundra - Heatmax...

Every one would like a new car (or truck) but some times it's not in the budget so you have to buy a used one or two for less money to get you by until your situation allows you to buy brand new. Yes, you may spend a little more in the long run but at least you never have to walk ;) I def want...

www.hearth.com

nelraq here again.....thanks to all of you that helped me out.

I have been using a fence staple...approx 1/8”...to slow the burn down. On the explosion event ...in trying to get more hours of burn time/heat....I took the staple out about 3/4s thru the burn. My mistake!

I am running the furnace again today...this time with a piece of rigid wire which is about 1/16th” wide. Seems to be working ok. Hopefully a flame will be in there till close to end of burn!!

 

[Wood1Dennis]

I would be concerned about fixing the damper to prevent it from closing down all of the way. I use a wire or nail to prop the damper wide open, but only when loading the furnace and getting the fire going. Once it is burning good and the secondaries are going I take it out letting the servomotor hold it open. I don't even like leave the furnace alone with the damper propped open because I don't want to forget.

I want the damper to close when the t-stat no longer calls for heat, but even more importantly, I want the damper to close all of the way if the furnace gets hot and triggers the over temp circuit to shut down the damper. Even when fully closed, it lets some combustion air in.

I suppose my perspective is different because I don't have a back burn problem. But I would be careful about a mod that does not allow the damper to close all of the way. My thoughts only, YMMV.

 

[brenndatomu]

But I would be careful about a mod that does not allow the damper to close all of the way. My thoughts only, YMMV.

That's why I said 1/8 - 3/16" is too much...but once the moisture is burnt off the load, look out, inferno ahead!
Propping the width of a paper clip allows minimal extra airflow though...but you are right, it's still overiding factory safety controls to some degree...it would especially bother me if I didn't have my chimney draft under control at all times, like some don't...

 

[laynes69]

I use a paperclip and anything larger than 1/16 of an inch is too much. Now if temps would drop for us below zero and I know the damper will cycle, I wouldn't need it. Even at times with a 1/16 inch gap can be too much.

 

[3fordasho]

I use a paperclip and anything larger than 1/16 of an inch is too much. Now if temps would drop for us below zero and I know the damper will cycle, I wouldn't need it. Even at times with a 1/16 inch gap can be too much.

I've used a paper clip on my shop tundra install but there has been a time or two during abnormally cold and windy conditions where even after removing the paper clip the furnace was approaching overfire conditions. In those events I would cover the secondary air inlets about 50% with aluminum tape. A barometric damper would have solved it but I never installed one.

 

[Wood1Dennis]

That's why I said 1/8 - 3/16" is too much...but once the moisture is burnt off the load, look out, inferno ahead!
Propping the width of a paper clip allows minimal extra airflow though...but you are right, it's still overiding factory safety controls to some degree...it would especially bother me if I didn't have my chimney draft under control at all times, like some don't...

Agreed! With a full load on a cold day she will burn plenty hot with the damper open only a sliver. To accommodate the variations (how hot I want to burn it, size of the load, weather conditions, etc.) I added a manual adjustment to control how far the damper on my Caddy opens. But even with the adjustment it will still close completely whenever the servomotor shuts it down.

 

[laynes69]

I've used a paper clip on my shop tundra install but there has been a time or two during abnormally cold and windy conditions where even after removing the paper clip the furnace was approaching overfire conditions. In those events I would cover the secondary air inlets about 50% with aluminum tape. A barometric damper would have solved it but I never installed one.

In the past I have used aluminum tape to close a portion of the secondary air and reduce some primary air to control the burn without a baro. The baro does make things much easier.

 

[Boilers]

I don’t understand how you still have combustible gas in there several hours into the burn cycle.... maybe I misunderstood something.

I have the Heatmax II also... installed in the basement with a barometric damper. I run a nail through the automatic damper hole all the time. It may be ~1/8” or slightly less. With the foam gasket material, it’s doesn’t let in too much air for me, but again, I have a baro. Only time I ever had explosions was in the beginning when I’d close the damper too early, causing the flame to go out before the damper reopened. Watching that damper open and the firebox fill with smoke gives you a helpless feeling .

I have since installed a controller and programmed a start sequence. I hit a start button and the furnace starts a ramping sequence based on flue temp. Starts hot and slowly lowers temp setpoint. It works well, but it’s only as consistent as the wood you feed it with... never explodes or puffs though.
Couple things to consider... when loading, do not block the small air inlets in the firebox. There’s one in front and one in back of the firebox. Without this air, your flame is more likely to go out.
Loading wood too tightly can also reduce flame and lead to a puff situation. It’s a balance. Wood will also burn up faster if you load it too loosely.
As already mentioned, the wood itself is the last factor, and it’s a big one. The wetter it is, the harder it is to hold a flame, and the more it’ll smoke. I don’t know the science behind it, but wet wood will definitely be more likely to puff vs dry wood.

 

[brenndatomu]

I have since installed a controller and programmed a start sequence. I hit a start button and the furnace starts a ramping sequence based on flue temp. Starts hot and slowly lowers temp setpoint.

Stepper motor, or short intermittent blasts of wide open damper?

 

[Boilers]

Stepper motor, or short intermittent blasts of wide open damper?

it just cycles the damper fully open/closed. Next mod will be some sort of true servo or linear actuator to vary damper 0-100%. It would be so nice to just give it a setpoint and and have it maintain that temp by opening the damper only the necessary amount. The open/closed (on/off) control is painful.
Or maybe just order a VF100 ! With the rebates and sale of the Heatmax, the price becomes fairly reasonable.