Cat... smolder burn

[woodmiser]

Been reading about cat stoves and the ability to "smolder burn". Does this still produce substantial heat?
Is there such a thing as a retrofit cat that can plug into the top of the flue exit?

 

[spirilis]

there are "retrofit cats" that were usually a section of stovepipe, they made a lot during the 80's when cats were new, my understanding is they don't work very well as they struggle to keep up to temp (and there's no separate source of heated secondary air for them in most stoves, so when you damp it down to smoulder the wood you're also cutting what excess air the cat would need to combust)

I know woodmanspartsplus.com carries one ("Add-On Catalytic Damper") in 6" and 8" flue sizes.

Seems most well designed cat stoves keep the catalyst close inside the stove, but preferably out of reach of flames so the catalyst doesn't become damaged by impinging flames, and they have some kind of preheated secondary air source injecting close to the cat I think.

 

[SolarAndWood]

Smolder burn might bring to mind the things you do with a smoke dragon to get a longer burn, this isn't what happens in a cat stove. The stove burns cleanly at low burn with no visible flames. The same stove I get 24 hour burn cycles with chunk punk and uglies in October can kick down and do 12 hour burn cycles with the good stuff in January at something on the order of 8 times the burn rate.

 

[woodmiser]

But does it heat when in low burn when no flames are present?

 

[SolarAndWood]

Absolutely. In fact, it is much more common to not see flames in my stove and only see something like this.

 

[SolarAndWood]

This is what a raging fire looks like.

 

[jharkin]

Absolutely throws heat when there are no flames visible in the firebox. There are flames on the other side of the cat you just don't see it.

The only time I see a lot of flames is when the stove is cranking on a cold day. Mild days we only really get the flames shows on the reload when I'm warming it back up.

 

[woodmiser]

So when winter really sets in how often do you go into slow mode? Every night? Is that enough to keep up?

 

[SolarAndWood]

I try to stay on 24 hour burn cycles. Right now that means burning chunk, punk and uglies. As it gets colder, the fuel gets better. When the good stuff isn't enough to keep the house warm, I go to 12 hour burn cycles. The stove has an advertised 4.3 cu ft box. When you burn that much good wood in 12 hours, you are putting a lot of heat into the building (at that burn rate, you are talking 1/2 a cord a week of wood). The big benefit of the cat is that that same stove can also do the job in October without building small fires or overheating the house.

 

[jharkin]

That depends on your setup. Your climate, the size and how well insulated your house is and the output rating of your stove.

Give you an example. I'm near Boston, about 5500 degree days per heating season.
House is small - 1400 ft2, *was* drafty and partially uninsulated.
My stove is 65k BTU output, rated ot heat up to 1800ft2 (those ratings are based on average insulation in a mild climate like Virginia).

- if its in the 50s out the stove will overheat us.
- Days that its in the low 40s with lows around 30 overnight I can cruise on low all day maintaining 70-75F indoors (solar gain makes a big difference in this range).
- Midwinter when the highs are 20-30 and the lows are in the teens I need to burn med-high daytime and low overnight will get me through with coals and the indoor temp dropping into the mid/high 60s.
- When we get those cold spells where it drops close to zero I have to really crank and maybe even turn on the gas heat to even out the house in the morning (upstairs gets cold).


This year we insulated the house so I expect that I wont need to supplement with gas on the coldest days anymore.

 

[Backwoods Savage]

But does it heat when in low burn when no flames are present?

We find it very easy to reach 700 degree stove top temperature even without any visible flame. That certainly is enough heat for us.

 

[bogydave]

This is a pic of just into the long burn cycle. 10 PM last night. No flames.
The catalytic is glowing red hot (like in the above pic), producing lots of heat. Stove is hot.
No flames, I can touch the stove pipe, no visible signs out the top of the chimney that I'm burning (clean burns)
The wood is burning more like charcoal, just enough air to burn but not enough to flame & very little heat go up the flue. The cat-combustor is burning the smoke & wood vapors & the heat is mostly released into the house.
18° last night, plenty of heat all night & still putting out heat past noon today.
It truly is amazing, but more heat from this stove with the 40% + less wood thru the year.
Now the wood has to be dry, but I still am amazed when I get the 20+ hour burns with the outside temps in the teens.
I don't believe it works, I know it works!

 

[HotCoals]

Dave,
By your pic I assume you loaded it up some before the pic..half hour or so?
I get the same smoke on the glass after reloads..even after gassing off for a 1/2 hour.
It's almost like the air wash is moving the smoke to the glass because the center stays clear for a long while.
I dunno..but I don't care because its heats so well.

 

[leeave96]

My experience with the smolder burn on my cat Keystone is that you are only intensely radiating heat from one surface vs the whole stove - which is a desirable thing. On the Keystone, the cat is right under the top of the stove, so I can damper the stove down and get a 500 to 600+ cat only burn. It usually settles down to 500 degrees and stays there for hours. This is all the heat I need or want in milder temps or just to keep the chill at bay overnight. That's the beauty of a cat stove - more clean burn control at low temps. If I need more heat, I turn it up and the stove box temps heat the rest of the stove body for much more heat radiating out. When in low burn, I can easily get an 8+ hr burn on a stove with only a 1.5 cu ft firebox.

Also, on my stove (and I think other cat stoves), a bit of free air comes into the stove via a small hole in the ash pan housing. This ensures some air for smolder combustion to keep things going if I turn it down to much and greatly helps the coals burn to ash.

I think if my house where the Keystone is located had more than a shread of insulation, the smoldering burn's heat would be better captured and we'd have a stove that would appear to do more on the super low burn than simply knock off the chill.

I highly recommend a cat stove - if for nothing else, the ability to turn the stove down for very clean lower heat output smoldering burns when needed/wanted.

Bill

 

[jimbom]

...I can touch the stove pipe...

Awesome. No matter what I do, I cannot get my connector surface below 230 °F or so. I know heat up the chimney is necessary to carry out the moisture and power the flue, but I sure would like to keep it to the minimum.

 

[bogydave]

Dave,
By your pic I assume you loaded it up some before the pic..half hour or so?
I get the same smoke on the glass after reloads..even after gassing off for a 1/2 hour.
It's almost like the air wash is moving the smoke to the glass because the center stays clear for a long while.
I dunno..but I don't care because its heats so well.

Roger that; I didn't get a pic, last night, of it on high, & just full of flames in bypass closed mode.
But here's a Pic 10 min after I turned it down from high to 2.25
Then a pic, just minutes ago, getting ready to empty the ashes in about 2 hours after 11 days of burning of the coals I raked to the front. (cat temp mid range)
More coals than normal so heating the house pretty warm now, on high but trying to get in done while it's still daylight.
Flash don't do it justice, it's cherry red coals & too hot to get in to empty ashes.
Pic 1 was 10 pm last night, pic 2 is 3:30 pm today 2 hours of burn cycle left to go to have less coal so I can empty ashes..

 

[Todd]

I find if I turn it down too soon to a smoulder cat burn my glass will fog up like you Blaze King guys get, but if I burn for an hour with good flame then turn it down the glass will stay clean. I still get a nice long burn this way and I hate to see dirty glass, just bugs me.

 

[woodmiser]

I would think the smolder burn will have some negatives with respect to creosote in the firebox before the cat. Any issues there? So far it looks very impressive that you can burn that way.

 

[Todd]

Yeah, you can get a little creosote inside the fire box but it doesn't hurt a thing. It burns off when you start burning hotter. I'm more worried about creosote after the cat which for the last 6 years has been little to none.

 

[WoodpileOCD]

Absolutely. In fact, it is much more common to not see flames in my stove and only see something like this.

+1
My temptation at first was to want to poke the fire but now I restrain because it is heating so well .

 

[jtb51b]

Dave,
By your pic I assume you loaded it up some before the pic..half hour or so?
I get the same smoke on the glass after reloads..even after gassing off for a 1/2 hour.
It's almost like the air wash is moving the smoke to the glass because the center stays clear for a long while.
I dunno..but I don't care because its heats so well.

Roger that; I didn't get a pic, last night, of it on high, & just full of flames in bypass closed mode.
But here's a Pic 10 min after I turned it down from high to 2.25
Then a pic, just minutes ago, getting ready to empty the ashes in about 2 hours after 11 days of burning of the coals I raked to the front. (cat temp mid range)
More coals than normal so heating the house pretty warm now, on high but trying to get in done while it's still daylight.
Flash don't do it justice, it's cherry red coals & too hot to get in to empty ashes.
Pic 1 was 10 pm last night, pic 2 is 3:30 pm today 2 hours of burn cycle left to go to have less coal so I can empty ashes..

I remember those days, and I sure wish mine would go back to burning like that! I get mountains of coal and takes a ton of time and air to burn them to ash.. It wasn't like this when I first installed the stove.. I can burn low and long but I don't get the heat output I used to either. I have to turn the stove up to get heat..

Jason

 

[Backwoods Savage]

I would think the smolder burn will have some negatives with respect to creosote in the firebox before the cat. Any issues there? So far it looks very impressive that you can burn that way.

No problem with creosote here at all. The firebox stays clean and we do not have that problem with the glass as ours stays clean. No black and no fog. Occasionally we do have to clean the fly ash off the glass but that is all.

In addition, we've burned our stove for 4 winters (24/7) now and have cleaned our chimney one time and there was no creosote. That, I believe is one big benefit of the cat stoves.

 

[bobforsaken]

Can someone speak to whether or not all CAT stoves should be able to maintain a smolder burn with no flame as described above. I have a Jotul Firelight 12 and I usually operate air about 1/4 open and can get a nice hot (600 degree stove top or so) burn for several hours with nearly no smoke out the chimney.. However I ALWAYS have flames, albeit usually just a single small tongue of flame with the cat active. When I've choked it down too far (all closed) I've ended up with lots of smoke and the fire cools off outside of the CAT active zone.

Is it the fact that I just have a different stove that I can't "smolder burn" with no flames, or is it something I'm doing wrong or wrong with my stove.

For the record its a brand new steel cat in there right now.

Also of note.. When I operate with too little air I will get no flame.. then a burst of fire.. then no flame. These "explosions" usually only happen when its 30's or warmer outside.

 

[BrowningBAR]

Can someone speak to whether or not all CAT stoves should be able to maintain a smolder burn with no flame as described above. I have a Jotul Firelight 12 and I usually operate air about 1/4 open and can get a nice hot (600 degree stove top or so) burn for several hours with nearly no smoke out the chimney.. However I ALWAYS have flames, albeit usually just a single small tongue of flame with the cat active. When I've choked it down too far (all closed) I've ended up with lots of smoke and the fire cools off outside of the CAT active zone.

Is it the fact that I just have a different stove that I can't "smolder burn" with no flames, or is it something I'm doing wrong or wrong with my stove.

For the record its a brand new steel cat in there right now.

Also of note.. When I operate with too little air I will get no flame.. then a burst of fire.. then no flame. These "explosions" usually only happen when its 30's or warmer outside.

Every cat system is a little different.

"Single small tongue of flame with the cat active" seems very normal.

 

[bogydave]

Dave,
By your pic I assume you loaded it up some before the pic..half hour or so?
I get the same smoke on the glass after reloads..even after gassing off for a 1/2 hour.
It's almost like the air wash is moving the smoke to the glass because the center stays clear for a long while.
I dunno..but I don't care because its heats so well.

Roger that; I didn't get a pic, last night, of it on high, & just full of flames in bypass closed mode.
But here's a Pic 10 min after I turned it down from high to 2.25
Then a pic, just minutes ago, getting ready to empty the ashes in about 2 hours after 11 days of burning of the coals I raked to the front. (cat temp mid range)
More coals than normal so heating the house pretty warm now, on high but trying to get in done while it's still daylight.
Flash don't do it justice, it's cherry red coals & too hot to get in to empty ashes.
Pic 1 was 10 pm last night, pic 2 is 3:30 pm today 2 hours of burn cycle left to go to have less coal so I can empty ashes..

I remember those days, and I sure wish mine would go back to burning like that! I get mountains of coal and takes a ton of time and air to burn them to ash.. It wasn't like this when I first installed the stove.. I can burn low and long but I don't get the heat output I used to either. I have to turn the stove up to get heat..

Jason

A combustor last about 2-1/2 to 3 years before it starts to deteriorate. I've read the 10,000 to 12,000 hours life span of the combustors on a few university studies also.
A good read for those with over 3 year old combustorslast few paragraphs) (cost study link on the page too)
http://www.woodstovecombustors.com/How_They_Work.html