Green Mountain 80 clogged CAT sections w pics

[Untamed]

I have the Green Mt 80. When the stove was new and gaskets all tight the stove performed better and the cats didn't plug until the 2 month mark. Now into the second burn season I have to clean them about every 2 weeks. The door and combustor gaskets were hanging off after the first week of fires. When I test the door gasket by latching with a piece of paper in between it easily pulls out.

I emailed Hearthstone and they just said don't engage cats until the fire is hot. I wait until the gauge is maxed before engaging cats and it hasn't made a difference. Going to put new gaskets on and test that out. Meanwhile were a month into our 6 month burn season and I'm shopping for a BK 40.

 

[begreen]

It's not necessary to wait until the cat indicator is at maximum. That can be a waste of fuel. Once it's in the active zone, close the bypass.

Increased cleaning requirement can be an issue with the wood burned. Some species create more ash than others.

 

[JDeere19]

Of course, this happened right when we were getting single digit temps. Thankfully, we should be returning to 30's - 50's by the end of this week. Here's what was happening.

1. CAT temp would be in the active range. Flame was going good. As soon as I engaged the CAT all flame would move to above the wood (secondary) and roll for a few minutes and disappear.

2. Stove would not get up to normal temps with the CAT engaged.

3. Horrbile amounts of coal build up. Single digit temps might've attributed to this.

I knew this was the issue. See below.

View attachment 306242

All 3 CAT sections were as bad as the one to the right.

View attachment 306243

All Clean. I used a shop vac and actually a plastic bristle brush because they needed a light amount of scrubbing. You're supposed to be gentle on these things when you clean them. Also, the one on the right looks worse from an angle. If you're directly under it, it will look like the one on the left.

I started burning at the end of October. I was for the past couple of months cleaning the ash out every day but I would try to sift through it and try to slide the coals over the top to the side so I can save them for re-loading/lighting. I've encountered this issue before. I think I'm gonna try to just not play in the ashes as much as possible. If the ash is hot it floats up a lot. Anyways just sharing so people with this model know what's to come. Take care guys!

I've had this same issue. Seems worse when you sift through the coals to get ash dust out and keep actual coals in. They will always clog at some point I feel like, but I've noticed this drastically speeds that up

 

[Untamed]

Hearthstone said I was engaging to soon. When reloading stove burn wide open for 15-20 minutes before re- engaging cat. They want me to burn up my wood before the cat should be re-engaged. One Hearthstone vendor told me to only burn oak in this stove.

I don't mind trying a few things. If it's the type of wood burned causing the plug issue then I have no choice but to look for a better design. The next step will be to remove it and bring in a new stove.

 

[Todd]

I have the Green Mt 80. When the stove was new and gaskets all tight the stove performed better and the cats didn't plug until the 2 month mark. Now into the second burn season I have to clean them about every 2 weeks. The door and combustor gaskets were hanging off after the first week of fires. When I test the door gasket by latching with a piece of paper in between it easily pulls out.

I emailed Hearthstone and they just said don't engage cats until the fire is hot. I wait until the gauge is maxed before engaging cats and it hasn't made a difference. Going to put new gaskets on and test that out. Meanwhile were a month into our 6 month burn season and I'm shopping for a BK 40.

Seems many of these hybrids are having issues. I really don’t like the cat setup under the flue collar, just seems like a bandaid fix and another problem down the road. If this is your primary heat source probably is a good idea to shop for something new. BK King is a great stove but I’d also look into some of the better big non cats like Lopi, PE and Jotul if your looking for a more of a KISS stove with less maintenance.

 

[Ashful]

Sorry, I just saw this thread. Cats clogged with fly ash are often the result of too much draft, essentially the strong draft creates a higher than intended air velocity through the air wash, stirring up fly ash, which is then pulled into the cat by chimney draft. But your description of 11-12 feet of total pipe with two 90's, a cleanout, and two more 45's doesn't sound like anything that could possibly ever over-draft a stove.

begreen's assumption of stirring up too much ash while working in the stove would be a good one, if you were forgetting to open the bypass before opening the stove. But with bypass open, there should be effectively zero draw on the cat. Wait 5 minutes after loading and closing the door, before ever closing bypass to avoid this, and other issues with thermal shock.

 

[begreen]

Seems many of these hybrids are having issues. I really don’t like the cat setup under the flue collar, just seems like a bandaid fix and another problem down the road. If this is your primary heat source probably is a good idea to shop for something new. BK King is a great stove but I’d also look into some of the better big non cats like Lopi, PE and Jotul if your looking for a more of a KISS stove with less maintenance.

Kuma, Woodstock, Lopi, & Regency Pro have good hybrid designs.

 

[rashomon]

I wanna mention I have a GM60 and it's my second season. I've only ever burned pine and much of it was still wet last year. I had the worst time with smoke and trying to get my fires started. I was certain my Cats took a hit and my chimney needed bad cleaning. Towards the end of the season I had some better wood and we finished out the season.

When I did my first cleaning a month ago I was very surprised to see my cats were perfectly clean. I couldn't believe it. My chimney had maybe 1/4" of creosote at worst which I brushed up easy.

So I'm surprised your GM80 is so bad. (I do wish I got the 80, my 60 isn't enough).

I do not rake the coals while the fire is going, never even thought of it. I just add more and more wood, maybe occasionally push it to the side. The next morning is when I try to remove the ash and yes it creates a nasty ash cloud unless I'm extremely careful, but I have the bypass engaged so ash either goes up the warm chimney or floats into my home.

I do like to save the chunks of coals usually cold by now. I use a small rack from a toaster oven to sift, but it's a mess. I wish there were an easier way.

 

[begreen]

Thanks for the report, this is helpful information.
There are several coal scoopers on the market. Some folks use kitty litter scoopers. This one is all metal.

Amazon product ASIN B085QMHV38

 

[webby3650]

Sorry, I just saw this thread. Cats clogged with fly ash are often the result of too much draft, essentially the strong draft creates a higher than intended air velocity through the air wash, stirring up fly ash, which is then pulled into the cat by chimney draft. But your description of 11-12 feet of total pipe with two 90's, a cleanout, and two more 45's doesn't sound like anything that could possibly ever over-draft a stove.

begreen's assumption of stirring up too much ash while working in the stove would be a good one, if you were forgetting to open the bypass before opening the stove. But with bypass open, there should be effectively zero draw on the cat. Wait 5 minutes after loading and closing the door, before ever closing bypass to avoid this, and other issues with thermal shock.

We get calls from almost everyone of the green mountains we’ve installed. All different flue types, all clogged cats after a short amount of time. They don’t use a traditional bypass, it’s very small. 4”x4” I’d say and it’s above the baffle between the cats. Smoke and ash still have to travel around the baffle even bypassed. Then the cats are positioned directly under the flue catching all that falls.. Another issue, everyone one we’ve installed has had the bypass gasket fall off after the first fire or 2. There is no access to it without removing the top of the stove. You have to do it blind through the front door. Just a terrible design. The Manchester has the cats laying flat above the baffle away from the flue collar, still clog very easily. Again, no actual bypass of the baffle in this design either.

 

[tabner]

MY GM60 spilled a lot of smoke and ash into the room on reloads. As In - fly ash on the furniture surfaces in the room the stove sat in. BK Ashford on the same exact flue setup, no issues, I can open the front door with a load still burning and nothing more than a minor/brief smoke smell escapes.

 

[klitscher]

I wanna mention I have a GM60 and it's my second season. I've only ever burned pine and much of it was still wet last year. I had the worst time with smoke and trying to get my fires started. I was certain my Cats took a hit and my chimney needed bad cleaning. Towards the end of the season I had some better wood and we finished out the season.

When I did my first cleaning a month ago I was very surprised to see my cats were perfectly clean. I couldn't believe it. My chimney had maybe 1/4" of creosote at worst which I brushed up easy.

So I'm surprised your GM80 is so bad. (I do wish I got the 80, my 60 isn't enough).

I do not rake the coals while the fire is going, never even thought of it. I just add more and more wood, maybe occasionally push it to the side. The next morning is when I try to remove the ash and yes it creates a nasty ash cloud unless I'm extremely careful, but I have the bypass engaged so ash either goes up the warm chimney or floats into my home.

I do like to save the chunks of coals usually cold by now. I use a small rack from a toaster oven to sift, but it's a mess. I wish there were an easier way.

This is nearly my exact experience I have a GM80 in my second season. It's my first stove (so it took me a bit to figure out how to run it well) and we love it. We're in Tennessee so we don't see consistent cold temps, but we haven't turned the furnace on in a ~4,000 sq ft house yet. I did my first cleaning a few months back at the beginning of the season and my Cats were perfectly clear as well. Barely any creosote either. I would be surprised that the Cats get covered by ash unless one isn't engaging the bypass with the door open. I have the Koal Keeper scoop and whenever I try to sift with hot coals we get ash all over the hearth and flying around on top of the stove. I don't think the design is great as I really have sift it well to get the ash out. I'd rather just let the coals burn down and cool and then scoop out then.

I'm getting ~8-10 hours burn time while still in the Cat range and have had coals in the ash for up to 36 hours after loading. It's been easy to light as well. We really do like this stove and love the large glass which shows off the secondary burn beautifully. I hate others aren't having the same experience.

 

[Ashful]

I hate others aren't having the same experience.

Totally understandable. Based on @webby3650's response, I'm guessing the successful operation of this stove is probably strongly dependent upon the conditions of installation and wood being burned. You have lucked out in providing this stove with optimal conditions for success, be it chimney height and other parameters, but perhaps the window for success is relatively small compared to other more forgiving designs.

 

[Wisco Shepherd]

Kuma, Woodstock, Lopi, & Regency Pro have good hybrid designs.

My Kuma has not clogged and I admittedly fiddle with my ash too much.

Thats one typo away from sounding very wrong

 

[begreen]

Thats one typo away from sounding very wrong

😄 I had to read it twice.

 

[webby3650]

Installed a new hybrid Mansfield yesterday. 3 cats sitting vertical under the flue. Blowing that extra heat straight up the pipe! And all the crud falls into the cat… replacement cost is around $800! 👎

 

[begreen]

What is stopping common sense in these stove? Patents already taken for the good designs? Regency has a couple like this too.

 

[Todd]

Yeah seems like a bandaid fix to pass 2020 regs and get a tax credit. I foresee many people just removing the cat and burning without after it dies. At least it will still burn pretty clean since it’s a hybrid. They will probably draft better without the cat as well.

 

[Ashful]

Yeah seems like a bandaid fix to pass 2020 regs and get a tax credit.

I agree. We see this in stoves from the early 1990's, when VC and Jotul were some of the first to add catalytic combustors to existing designs. Huge problems, and terrible reliability, although they were getting pretty good performance when everything managed to work for a few weeks after a cleaning. But they improved and I have no doubt Jotul will dig their way out of the present F500 issues, it's just a temporary bump along the road.

 

[klitscher]

This is nearly my exact experience I have a GM80 in my second season. It's my first stove (so it took me a bit to figure out how to run it well) and we love it. We're in Tennessee so we don't see consistent cold temps, but we haven't turned the furnace on in a ~4,000 sq ft house yet. I did my first cleaning a few months back at the beginning of the season and my Cats were perfectly clear as well. Barely any creosote either. I would be surprised that the Cats get covered by ash unless one isn't engaging the bypass with the door open. I have the Koal Keeper scoop and whenever I try to sift with hot coals we get ash all over the hearth and flying around on top of the stove. I don't think the design is great as I really have sift it well to get the ash out. I'd rather just let the coals burn down and cool and then scoop out then.

I'm getting ~8-10 hours burn time while still in the Cat range and have had coals in the ash for up to 36 hours after loading. It's been easy to light as well. We really do like this stove and love the large glass which shows off the secondary burn beautifully. I hate others aren't having the same experience.

FWIW, shortly after I posted this it seemed like my stove wasn't drafting well with cat engaged. I let it cool down and had a ton of fly ash on the cat. A quick brush and it was gone and burning much better. Still love the stove. It hasn't been above 35F the past week or so here and I've been easily able to keep the house in mid- to high-60s in the areas furthest away from the stove.

Just wanted to provide an update after I said I had no issues with ash on the cat.

 

[Ashful]

Maybe a cool down and cat vacuum on some regular schedule is in order. I often end up doing that with one of mine once at mid-season each year.