How much of a problem is a broken catalytic converter?

[johnblacksox]

Hello,

I have a Lopi fireplace insert. This is my 3rd winter using it, and I light a fire every evening from November to March. I burn from like 7 PM til 11 PM, mostly for ambiance, not trying to maximize heat output or heat my entire house with it. When I go to bed, I open the bypass, and open the air intake all the way to let the fire burn out, as opposed to choking it to maximize heat overnight.

I noticed today when I took it out for vacuuming that the cat converter has a spot that is cracked and broken. The grid is cracked from top to bottom, and in the middle, there's like a 1 inch by 1 inch section that is broken to the point where it's crumbled/not functioning. The rest of the converter looks great, no other cracks, and the grid is completely clear of ash or debris.

I have no idea how/when this happened, but I suspect recently. Maybe even the guy who cleaned it this spring did it.

Can I still use it like this? Is it dangerous in any way? If I want to replace it, do I have to replace the entire thing, or just that one (removable) section that is broken? Do cracks/breaks like this happen through normal use? I don't burn crazy hot fires.

I'm thinking worst case, there's a small hole in the cat that exhaust goes straight through, but the rest of the cat still glows orange. So I'm thinking that its efficiency is slight less, but it's still working to some degree.

I can attach a picture if that helps.

Thanks in advance!

 

[begreen]

It's damaged, perhaps when the stove was cleaned, and should eventually be replaced. Which model is this? The combustor is likely one part, in spite of the dividers.

Pictures are welcome.

 

[johnblacksox]

Here's a pic. It's a Lopi large flush insert HybridFyre. You can see the broken part toward the right. The cat is maybe 3" high and about 21" long.

Ideally, I'll replace the cat at the end of this season, but I'm probably looking at burning 2 more cord of wood this season. Sound ok? Or should I replace it ASAP?

My main concern is danger, or damaging the stove or flue. If there's no danger or damage, then I'm happy to wait til spring.

 

[sourcehound]

Ceramic Catalytic converters seem to be prone to crumbling - I went through two in three years, and it's supposedly due to temperature fluctuations. It's possible that by opening the bypass instead of letting the fire burn overnight with the bypass closed is hitting the converter with temperature changes which led to the crumbling. My cats crumbled a bit slowly a few cells at a time - it still worked, but eventually a section fell out and I had to replace it the whole thing. I switched to a steel cat - it doesn't crumble but is slightly more expensive. I'm on year 3 now with the steel cat and still going strong.

 

[webby3650]

It won’t do damage by using it like that. Have you verified the door gasket is good? It should last 5 years or more under normal use.

 

[johnblacksox]

Yes, door gasket is good.

Here's a pic of it tonight...You can see a vertical crack on the left and the small crumbled section on the right. The rest of the cat is pristine.

So you think I could use this the rest of the season? Obviously I'll keep an eye on it to make sure it doesn't get worse.

 

[webby3650]

Yes, door gasket is good.

Here's a pic of it tonight...You can see a vertical crack on the left and the small crumbled section on the right. The rest of the cat is pristine.

So you think I could use this the rest of the season? Obviously I'll keep an eye on it to make sure it doesn't get worse.

View attachment 306784

There’s no problem with using it like it is.

 

[moresnow]

There’s no problem with using it like it is.

And zero reason to open the bypass at bedtime. Unless there is some reason I've never been let in on.

 

[webby3650]

And zero reason to open the bypass at bedtime. Unless there is some reason I've never been let in on.

There is no reason. Some people are scared of the fire I guess. Opening the bypass only makes the fire less efficient and uncontrollable.

 

[johnblacksox]

I guess I open the bypass because I thought it was better for the fire to burn out quickly, rather than smolder for hours.

Like for instance, they say not to engage the cat converter until the temp gets over 500. But if I leave the bypass closed at night, then the fire will slowly die out with the cat engaged, and the temp will be well below 500 degrees. So isn't that bad?

I'm happy to leave the bypass closed all night, I just thought it would create more creosote than letting it burn out quickly with an open bypass.

 

[moresnow]

I guess I open the bypass because I thought it was better for the fire to burn out quickly, rather than smolder for hours.

Like for instance, they say not to engage the cat converter until the temp gets over 500. But if I leave the bypass closed at night, then the fire will slowly die out with the cat engaged, and the temp will be well below 500 degrees. So isn't that bad?

I'm happy to leave the bypass closed all night, I just thought it would create more creosote than letting it burn out quickly with an open bypass.

Your Cat may certainly go inactive at the end of the burn/load. No issue as there is nothing left to create creosote in the load at that point. Enjoy your sleep!

 

[mdocod]

I guess I open the bypass because I thought it was better for the fire to burn out quickly, rather than smolder for hours.

Like for instance, they say not to engage the cat converter until the temp gets over 500. But if I leave the bypass closed at night, then the fire will slowly die out with the cat engaged, and the temp will be well below 500 degrees. So isn't that bad?

I'm happy to leave the bypass closed all night, I just thought it would create more creosote than letting it burn out quickly with an open bypass.

Almost every stove manual I have looked at on this subject has not been particularly forthcoming with what the complete burn cycle should look like or how it should be managed. They all describe a process for the initial system startup and dialing in a burn rate for operation or how to reload wood and fire it back up, but none of them address what to do as the flames die down and the fire transitions to a carbon-coaling phase. The missing component is whether or not your fire is actively combusting wood gases or is in carbon-coaling stages.

Maintaining a hot clean complete burn is critical for the wood gas (flaming) phase of the burn. This ensures you get the most heat, and put out the least emissions, and deposit the least possible amount of combustibles on your chimney system.

Once the wood has finished off-gassing, the strict operating procedures go away. You can do whatever you want with the coaling stage of the burn. For most of us, whatever low-steady burn rate was dialed in for the off-gas (steady flaming) part of the burn cycle will be left untouched to steadily burn through the coals cleanly and efficiently and hopefully leave us a few for an easier relight later. If, after the flames have gone out, you want to choke it down more to leave some lumps behind for later, that's fine, if you want to rake all the coals up into a pile to speed up their burn and break them down faster, that's fine, if you want to run the air control wide open on them, that's fine. It doesn't make much difference. This part of the burn cycle doesn't generate condensing gases and heavy particle emissions.

I've read about and even witnessed people trying to maintain an EGT above a certain number by constantly feeding wood, trying desperately to not violate the operating procedures, only to eventually run out of firebox space with a heaping mound of coals that won't drive high EGT's...

 

[begreen]

Yes, door gasket is good.

Here's a pic of it tonight...You can see a vertical crack on the left and the small crumbled section on the right. The rest of the cat is pristine.

So you think I could use this the rest of the season? Obviously I'll keep an eye on it to make sure it doesn't get worse.

View attachment 306784

Go ahead and use it. The pictures help. The damage is not as severe as it first sounded.

@webby3650 is there no flame shield protecting the cat on these Lopis?

 

[webby3650]

Go ahead and use it. The pictures help. The damage is not as severe as it first sounded.

@webby3650 is there no flame shield protecting the cat on these Lopis?

Nope. They’ve never used one and I rarely see one that’s failed.

 

[johnblacksox]

Ok, thanks everyone for the assistance! I'll continue to use it this season and replace in the summer. I'll also watch it, in case it gets worse.

Thanks also for the info on what to do with the fire overnight. I don't care at all about maximizing heat output, I use the fire mainly for ambiance, I don't try to heat my whole house with it. My main goal is safety overnight, and avoiding producing creosote or junk on the glass. So once I'm down to coals, and one or two mostly burned up logs, I usually leave the air intake wide open and open the bypass to send everything up the flue, then I go to bed. From what I understand, I can still leave the air intake wide open, but I'm better off leaving the bypass closed to send everything through the cat, correct? Or does it not even matter at that point? If the fire isn't hot enough to engage the cat, why not send it up the flue instead?

 

[mdocod]

Ok, thanks everyone for the assistance! I'll continue to use it this season and replace in the summer. I'll also watch it, in case it gets worse.

Thanks also for the info on what to do with the fire overnight. I don't care at all about maximizing heat output, I use the fire mainly for ambiance, I don't try to heat my whole house with it. My main goal is safety overnight, and avoiding producing creosote or junk on the glass. So once I'm down to coals, and one or two mostly burned up logs, I usually leave the air intake wide open and open the bypass to send everything up the flue, then I go to bed. From what I understand, I can still leave the air intake wide open, but I'm better off leaving the bypass closed to send everything through the cat, correct? Or does it not even matter at that point? If the fire isn't hot enough to engage the cat, why not send it up the flue instead?

Depending on the burn rate that was selected for your fire and the arrangement of the logs in the box, it's common for wood to still be off-gassing after the flames have gone out for awhile. Coals is not the same thing as a "mostly burned up log" in this context. If the log is still holding itself together and has some weight in it, (like, you can lift it with a poker), then it has not transitioned completely to carbon-burn yet. The stuff that produces wood gas is the stuff that holds wood together. From the time the flame goes out, to the time that that all the fuel has transitioned to carbon-phase (no visible smoke from coals), is the most important time to leave the cat engaged. The lingering wood gases during this part of the burn cycle are insufficient to maintain active flame in the firebox, but the pre-heated cat can burn these off cleanly. Let the cat do its job here! Minimize deposits on the chimney system and deliver more heat to the home in the process.

In my stove, after the flames drop out of the firebox, that's actually when the cat becomes the MOST active, and the temp probe above the cat shoots up higher during this part of the burn cycle. This often lasts an hour or 2 after visible flames have gone out in the firebox.

Most people would leave the cat engaged for the final coaling stage of the burn as this forces the warm exhaust coming off the coals to pass through the labyrinth rather than go right up the chimney. The longer path provides better heat extraction.

Also, running with the cat engaged provides an extra spark arrestor in the exhaust path, minimizing risk of anything making it out the chimney that is hot enough to start a fire outside. (This is a very low risk in most systems but it's easy to add even more risk mitigation by just leaving the cat engaged).

 

[johnblacksox]

Ok, that's a great explanation, thanks!

So basically, regardless the stage of the fire dying out, whether it's a couple logs still holding together, or just coals, it's fine or even preferable to have the exhaust go through the cat. So I will go that route.

 

[begreen]

Ok, that's a great explanation, thanks!

So basically, regardless the stage of the fire dying out, whether it's a couple logs still holding together, or just coals, it's fine or even preferable to have the exhaust go through the cat. So I will go that route.

Yes, leave the bypass closed and leave the air control as set, not wide open. It will burn down the coals at a steady rate and will take care of itself.