Need Woodstock AS help, at wits end.

[Chris1927]

I have a Woodstock AS. I’ve had it since they’ve come out. I love the company and the concept of the stove. The problem is probably me and I am too dumb a wood burner to figure things out. I have had all sorts of problems and I’m ready to give up on it and get rid of it. Frustrated! Need a simple noncat stove with an air control and that’s it.
Long story. In the second year with it, I noticed the secondary burn grate warped. Wood stock said it’s designed to flex. Then the metal warped at the bypass gasket channel. I don’t think I overburned it as it burned 500-550 STT until it warped and started reaching STT temps of 600-625. I brought it and it got repaired.
Burned it for another year and a half after that. Again it broke near the bypass channel. Again, I don’t think I overburned it, as the STT temps were 500-550. The stove got fixed again.
Another problem I had is I had condensation in the chimney on a cold start, so much so that it dripped back in through the thimble and I needed to build a dam inside to prevent it with refractory cement.
Before this burning season, I had the chimney lined with 6 inch preinsulated liner and I put in a fresh air intake. No more condensation. I think the fresh air intake was a mistake, but I put it in based on advice of people from forums. The STT temps were climbing to 600 a few times, and Woodstock says that’s potential warping temps. I disconnected the fresh air intake on advice of my chimney sweep to see what would happen.
Right now, on a hot reload, I can close the bypass almost immediately with the STT temp at least 250, shut the air down to half way between 0and 1 and the STT temps will reach 500-550 at peak.
But another problem I’m having is sudden ignition of secondaries, so much that it startles me when it happens. This happens even after I have cleaned the cat with vinegar and water, and I’m confident I didn’t shut the air down too quickly.
I’ve played with a key damper in the pipe to see if that helps, wondering if potential overdraft. But I’m not sure that is the answer. Seems to burn too low, and then I was using it and it had sudden ignition of gasses and smoke came out every orifice it could and scared the Dickens out of me. Wondering if something is broken somewhere, but I can’t figure it out. I don’t notice anything (other than the warped/flexed secondary burn grate/not sure if this would cause a problem).
This evening, I built a top down fire on a cold start. Let the pipe temp get to above 250, closed the air to just below 3, let STT temps get above 350, then chit the air to 2. Pipe temp rose to 325 and STT to 500. When it came out of cat mode, it came out with sudden ignition of gasses a little hard. Went back into cat mode, again came out a little hard but okay. Then back to cat mode, then came out with a “whoosh” that’s enough to scare you .
I’m about to give up.

 

[Chris1927]

Anyone have any thoughts, ideas what might be causing the sudden ignition of gasses?

 

[begreen]

600º SST is a daily occurrence with our stove with winter fires . That should not be close to trouble for a steel stove.

Describe the flue setup from the stove to the chimney cap, including and elbows. What is the overall height? Are there any other factors like basement install?

Who did the repair work, Woodstock?

 

[Chris1927]

About 18 inch rise from top of stove, 90 degree elbow, then about a foot to the snout? of the liner going into the thimble. Not sure the length of the snout to the liner itself, but it’s a little longer than usual. Chimney is about 25 feet? The liner inside must come down about 18 feet? to where it connects with snout. Preinsulated 6 inch liner. Stainless steel cap on top that came with the liner.
Stove installed in the living room. Cathedral ceilings. House is 3200 square feet lofted/open to the upstairs
House is built with SIPS.
I have a HRV.
Woodstock did the repairs.

 

[snobuilder]

Following

 

[begreen]

Does the stove have an outside air supply? If not, if a nearby window is cracked open an inch, does that improve stove behavior?

Has the wood been resplit and tested for moisture content?

 

[Chris1927]

I hooked up an OAK before this burning season. It seemed to be making it burn hotter (the occasional 600). I disconnected it to try it without it because my chimney sweep suggested it. Seemed to be able to keep the temps down a bit more so I left it. Stove has sudden ignition of gasses with OAK too, maybe even worse. I noticed that for a period of time when trying the pipe damper, the gas ignitions were more gentle, but then with the pipe/key damper, it exploded basically.
I have a Heat Recovery Ventilation System too. In Woodstock’s manual, that’s listed as a solution for a tight house.
Wood split and tested, less than 20% moisture.

 

[Chris1927]

I should say I recently changed the gaskets on the loading door and the ash pan door. Ash pan door needed it but changing it didn’t make a difference. Loading door gasket was okay but I changed it anyway.

 

[begreen]

I hooked up an OAK before this burning season. It seemed to be making it burn hotter (the occasional 600). I disconnected it to try it without it because my chimney sweep suggested it. Seemed to be able to keep the temps down a bit more so I left it. Stove has sudden ignition of gasses with OAK too, maybe even worse. I noticed that for a period of time when trying the pipe damper, the gas ignitions were more gentle, but then with the pipe/key damper, it exploded basically.
I have a Heat Recovery Ventilation System too. In Woodstock’s manual, that’s listed as a solution for a tight house.
Wood split and tested, less than 20% moisture.

An HRV can help, if properly balanced. Often they are not set for a wood stove's combustion needs. Some are adjustable, others are not. You can test this by cracking a nearby window open. If that makes a much more predictable fire, then the indication is the stove is choking for air. The OAK seemed to help albeit with higher SST. The 600ºF SST limitation is the strongest reason I see for disatisfaction with this stove. That is not very robust. The Progress Hybrid or Ideal Steel do not have this limitation. That said, you may be able to control SST by other means. For example, if the splits are larger that will slow down the fire.

Note that the manual lists 700º as maximum SST. It indicates Woodstock is concerned about this. If your SST is accurate, then 600º should not be warping components. FWIW, our SST hits 650-700º several times in cold weather burning with no sign of stress.

From the manual:
Burning a stove frequently at excessive temperatures is known as overfiring. When the surface temperature is consistently over 700  F, the stove has reached 1400  F inside. Operation with temperatures in this range can lead to metal warping, becoming brittle, and eventually deteriorating completely. It can shorten the useful life of the catalytic combustor.

 

[jalmondale]

I'm not sure if you've seen it, but Woodstock has an article on what I think you're describing (it sounds like backpuffing): https://www.woodstove.com/image/cat...Woodstock-Soapstone-Cures-For-Backpuffing.pdf - yours sounds like the last section with 'intermittent backpuffing'. If you try building smaller fires and running them with the air open a bit more, does that help? I'm not sure if that article applies to hybrids (I suspect it was written for just straight cat stoves), but it might be worth a shot.

 

[stoveliker]

I agree with the back puffing. Try to decrease the air slower, in smaller increments. (And thus starting a bit earlier to limit further rise of stt.)

 

[Chris1927]

The backpuffing happens when the stove is coming out of cat mode (black box). So, there’s waves of gasses igniting. They start strong, but not out of control, and seem to progressively get stronger until it comes out of cat mode and there’s continuous secondaries at the top of the fire box.
I just cleaned my cat. My chimney was recently cleaned so not likely to have obstructions. Seems to happen no matter the weather and no matter if I keep the air open more with a smaller fire or close air down more.

 

[Chris1927]

could it be related to a strong draft?

 

[stoveliker]

What do you mean by "it comes out of the cat mode"? Are you disengaging the cat by opening the bypass?

 

[snobuilder]

What is SST?

 

[stoveliker]

Typo. Should be STT, stove top temperature.

 

[Chris1927]

No. Sorry. I’m not opening the bypass back up. I’m trying to describe the cycles the stove goes thru after engaging the cat. First the viewing window goes black. I think this is what people refer to as cat mode. Then there’s waves of the firebox lighting up with secondary combustion then going black again. That’s when the backpuffing happens. Then the stove comes out of that and there’s steady rolling secondaries at the top of the firebox. Sometimes these can get quite strong. Then eventually the coaling phase.

 

[Chris1927]

I guess first step is to try it while hooking up the OAK again, letting the stove get up to temp to engage the cat, and not shutting the air too quickly. I guess I need to stop worrying about burning the stove too hot, but I’m sure you can understand my worry as I am really worried about it breaking again.

 

[stoveliker]

What is the timescale of the changes you see happening?

I would not call it "changing modes"; even when secondaries are going, the cat is still active.

It's a disbalance between gases production and air supply that results in a few oscillations of combustion efficiency in the firebox. Such (damped) oscillations are common in systems with slow time constants when parameters are changed too much/too quickly.

 

[Todd]

I think you need to burn the stove with a little more air. I used to see some back puffing with my Woodstock’s at lower air settings when the fire box was black. The gases can build up and overwhelm the cat thus the back puff. Try to find a setting where you still have a little flame For the first 30 min or so when you first engage the cat then try turning it down lower after that if needed.

Your temps sound fine not sure why you would have warping issues unless your cat temps are running high at those lower air settings overfeeding the cat? I remember seeing 700+ STT and 1500-1700 cat temps occasionally with a black fire box but it never lasted long and no warpage. This was also burning a Fireview and Keystone so the new hybrids could be a little different.

 

[begreen]

It sounds like the fire is dying down too much and smoke (wood gas) builds up in the firebox. Then a flame erupts from the hot coals and ignites the built-up wood gases in a small explosion. This is back-puffing. It is more common with poorly seasoned wood, but as noted this could be from other issues too, like the fire starving for air. This could be from the need for outside air or from turning down the air too much as you try to stop the stove from damaging itself. Given your previous repairs this is totally understandable. The secondary burn grate sounds fragile.

 

[Chris1927]

I think maybe like you said, I’m shutting it down (the air) too much and too quickly?
In previous years, I used to usually keep the air at 3 for a while, then shut down the air to whatever the ending position was.
Maybe I’ll try reconnecting the OAK and keeping the air open with visible flame like someone suggested for a half hour or so, or until STT climbs to 350-400. Then close air more.
Do people think shutting the air too quick would cause the cat to get clogged up with fly ash? This seems to have been happening to me often this year.

 

[stoveliker]

No, shutting too quickly does not give the fly ash problem. Over draft does. (Which is the reason for shutting down early...)

 

[begreen]

This is somewhat design dependent. An unprotected cat and too frequent ash cleaning can also cause ash plugging. Some species of wood create a lot more ash than others.

 

[Chris1927]

So I’ve suspected possible over draft, but I don’t know for sure. What do I do? How do I run it? I have a key damper in the pipe. I have talked to Woodstock about the draft. Lorin said she’d lend me a draft gauge if she ends up getting one (I guess she’s lent them out and often doesn’t get them back).

Some people I’ve listened to have equated closing the air and closing/turning the key damper as the same, limiting the amount of air. I don’t quite see it that way.

I think of it as a river. The current, how fast or slow it’s going is equivalent to the draft. An overdraft would be fast current. You can have the same amount of water in the River (the amount of air you let in) and it can be flowing fast or slow. Hope I make sense. I’m probably wrong.

So In my thinking, after engaging the cat, I would then maybe engage the key damper, no matter where the air setting is, even if I keep the air open and then close it down later. Because I want to slow the draft down.

But then how do we account for the stove “blowing up” when I last had the key damper engaged? Did I just build up too much fly ash in the cat over time and smoke came out wherever it could?