Is a catalyitic stove really more efficient since a cat looses its efficiency with age

[Fargo]

So as I am constantly thinking about wood stoves since my purchase, I am questioning the efficiency of catalytic stoves. I will preface by saying a lot of my research was done by chatgpt. So it could be completely wrong. But I have found that a cat can loose 10%-15% efficiency per year. I have also found that a stove with no cat or secondary burn may only be around 40%-50% efficient. So a stove like the BK Ashford 30.2 may start off at 83% efficient, but the stove itself might (my assumption) only be 50% efficient and the cat might be doing the other 33% of the work. If that is all true and the cat is loosing 10% efficiency over a 5 year period, a cat stove is only averaging 75.4% efficiency over that 5 year period. Or about the same as a clean non-cat like the Alderlea T6 (74%). (The 2 stoves I was considering). If my data is correct, it would seem to me, a cat should be replaced at a minimum of every 5 years to maintain efficiency.

What am I missing? If a cat looses 10% efficiency per year how is it more efficient than a non-cat, which as I understand does not suffer this type of loss. The break down looks something like this.

Given
Base stove efficiency = 50%
Catalyst adds = 33% when new
Total when new = 83%
Catalyst degrades 10% per year (multiplicative decay)

Summary: Efficiency Over 5 Years
Year Catalytic Efficiency Total Efficiency
0 33% 83%
1 29.7% 79.7%
2 26.73% 76.73%
3 24.06% 74.06%
4 21.65% 71.65%
5 19.49% 69.49%

Final Answers
Efficiency after 5 years: 69.5%
Average efficiency over the 5-year period: ≈75.4%

 

[EbS-P]

So as I am constantly thinking about wood stoves since my purchase, I am questioning the efficiency of catalytic stoves. I will preface by saying a lot of my research was done by chatgpt. So it could be completely wrong. But I have found that a cat can loose 10%-15% efficiency per year. I have also found that a stove with no cat or secondary burn may only be around 40%-50% efficient. So a stove like the BK Ashford 30.2 may start off at 83% efficient, but the stove itself might (my assumption) only be 50% efficient and the cat might be doing the other 33% of the work. If that is all true and the cat is loosing 10% efficiency over a 5 year period, a cat stove is only averaging 75.4% efficiency over that 5 year period. Or about the same as a clean non-cat like the Alderlea T6 (74%). (The 2 stoves I was considering). If my data is correct, it would seem to me, a cat should be replaced at a minimum of every 5 years to maintain efficiency.

What am I missing? If a cat looses 10% efficiency per year how is it more efficient than a non-cat, which as I understand does not suffer this type of loss. The break down looks something like this.

Given
Base stove efficiency = 50%
Catalyst adds = 33% when new
Total when new = 83%
Catalyst degrades 10% per year (multiplicative decay)

Summary: Efficiency Over 5 Years
Year Catalytic Efficiency Total Efficiency
0 33% 83%
1 29.7% 79.7%
2 26.73% 76.73%
3 24.06% 74.06%
4 21.65% 71.65%
5 19.49% 69.49%

Final Answers
Efficiency after 5 years: 69.5%
Average efficiency over the 5-year period: ≈75.4%

Life of the cat is roughly 10k hours. Do in a decade or 3 years. It doesn’t change the efficiency. The cat stoves are more efficient at lower operating temps. Burn less wood but you get replace a cat every 10k hours. They work well for some who don’t need lots of heat. Once you need to go to a 6-8 hour burn cycle the efficiency difference is less compared to a secondary burn stove.

The cat efficiency is just being measured how? Probably not the same way we measure stove efficiency.

 

[Fargo]

Life of the cat is roughly 10k hours. Do in a decade or 3 years. It doesn’t change the efficiency. ...

The cat efficiency is just being measured how? Probably not the same way we measure stove efficiency.

I don't know how the efficiency is measured, but surely they loose efficiency. They are made with materials that wear out and degrade. A used cat with 5000 hours won't work as well as a new cat, right???. Something must changed as the hours add on. Otherwise there would be no need to replace them. Unless you're saying a cat either works at 100% or it doesn't work at all. That would be a different scenario. But from my research, it appears a cat will loose its efficiency as it gets used up. So maybe the question is how much efficiency is lost at 10,000 hours? Is that when the cat is completely drained out and not doing anything? Is that closer to 50% loss of efficiency, or is it closer to 30% loss and your at the break even point of a non-cat? It seems to me a catalytic converter is a consumable item that wears out and looses its efficiency as it breaks down the materials. If so, the efficiency of the stove would have to be affected. So unless I'm completely wrong in my thinking, a cat stove will decrease in its efficiency as the cat breaks down. So its efficiency is kind of a decreasing number. Where a non-cat, with a secondary burner will have a more stable efficiency level through out its life. Sure the tubes or baffle can also wear out. And at that point they are not efficient and need replacing as well. But I think they are more durable will not suffer from loss of efficiency until completely gone. It seems to me the secondary burners either work or they don't. Otherwise, it would seem we would be replacing them as part or regular maintenance as well.

So I guess the question I am trying to figure out is how does the loss in the efficiency of the cat, or secondaries, affect the overall efficiency of the entire stove.

Note: I understand, the scenario I am trying to measure would require both stoves to be running at their optimal efficiency levels through out the test period (say 10,000 hours) The comfort of low and slow vs hot and fast could certainly affect efficiency as the secondary burner would likely drop out of its efficiency zone sooner as the firebox cools off. But lets assume, for the sake of argument, we are keeping both stoves warm enough during the entire 10,000 hours that both are maintaining optimal efficiency. How does loss of efficiency affect each stove.

In short, which is more efficient, a good quality catalytic stove with 9000 hours or a good quality non-cat, but secondary burner stove with 9000 hours?

 

[John Lehet]

Personally, I think chatGPT can draw itself a pixel bridge and go jump off of it. When we don’t have to worry about it spouting nonsense, maybe I will use it, but I’d rather not.

It’s like the cat in your car. It works, until it fails. When it fails, you replace it. I think what people see as the cats get older is that it’s harder to get them to light, takes slightly higher temperatures. So in that regard, you do lose a tiny bit of efficiency because you have to burn the fire longer without the cat. Like a non-cat stove. You can clean the cat, rinse it in vinegar in the case of my stove, to restore it, periodically, but eventually you get to a point where it’s hard to get it to light off at all.

I’ve been burning a non cat stove for the last 17 years, and before that I also had a non cat stove for some years. About 28 years ago I had a cat stove that worked very well, and then for a few years I had a very badly designed cat stove (Vermont Castings), which kind of soured me on catalytic stoves.

From my research, modern well designed cat stoves are much better than the early generation of catalytic stoves. I am replacing my stove with a hybrid stove, which features both secondary burning when the temp is high enough, and then uses the cat when the temps are lower. My current (non cat) stove needs to keep the temp higher all the time, so that often means burning a hot fire and then letting it go out. With this stove I don’t have to worry about the cat wearing out, but I’m definitely burning at lower efficiency and with less flexibility. Also catalytic stoves (with a bigger fireboxes) are better for burning overnight. This is something I want to do, since I live in a cold climate.

I fully expect that my new hybrid stove will give me more heat using less wood (which means less work). I also expect I will have to replace the cat after some winters. In the case of my incoming stove, that’s very easy and costs $200. I will have saved at least $200 worth of wood and had an easier and more comfortable time of it. Others may well want to avoid a cat, as I have for the last many years. Lucky we have many choices.

 

[Fargo]

I hear you on chatgpt. I take everything it says with caution. That is why I mentioned it was the source of my info. So I'm totally open to being wrong here. Infact, since I just ordered a Blazeking Ashford 30.2, I hope I am wrong about the cat loosing its efficiency. But it made sense to me. So I had to pursue the idea.

I see what your saying in regards to the cat. As long as its lighting up its doing something. I could even understand if a failing cat just means higher temps to light. So I guess the real question is, does a cat actually loose its efficiency or does it just get harder to light until it just doesn't work any more. Thanks for your thoughts.

 

[Sim]

Personally, I think chatGPT can draw itself a pixel bridge and go jump off of it. When we don’t have to worry about it spouting nonsense, maybe I will use it, but I’d rather not.

It’s like the cat in your car. It works, until it fails. When it fails, you replace it. I think what people see as the cats get older is that it’s harder to get them to light, takes slightly higher temperatures. So in that regard, you do lose a tiny bit of efficiency because you have to burn the fire longer without the cat. Like a non-cat stove. You can clean the cat, rinse it in vinegar in the case of my stove, to restore it, periodically, but eventually you get to a point where it’s hard to get it to light off at all.

I’ve been burning a non cat stove for the last 17 years, and before that I also had a non cat stove for some years. About 28 years ago I had a cat stove that worked very well, and then for a few years I had a very badly designed cat stove (Vermont Castings), which kind of soured me on catalytic stoves.

From my research, modern well designed cat stoves are much better than the early generation of catalytic stoves. I am replacing my stove with a hybrid stove, which features both secondary burning when the temp is high enough, and then uses the cat when the temps are lower. My current (non cat) stove needs to keep the temp higher all the time, so that often means burning a hot fire and then letting it go out. With this stove I don’t have to worry about the cat wearing out, but I’m definitely burning at lower efficiency and with less flexibility. Also catalytic stoves (with a bigger fireboxes) are better for burning overnight. This is something I want to do, since I live in a cold climate.

I fully expect that my new hybrid stove will give me more heat using less wood (which means less work). I also expect I will have to replace the cat after some winters. In the case of my incoming stove, that’s very easy and costs $200. I will have saved at least $200 worth of wood and had an easier and more comfortable time of it. Others may well want to avoid a cat, as I have for the last many years. Lucky we have many choices.

Why did you decide to get a hybrid stove vs catalytic for your new stove?

 

[EbS-P]

The way the cat works is it provides a reaction site, while at the site it requires less energy to break apart the molecules. So at the site by site level yes it is an all or nothing reaction. As the cat ages my guess is the number of reaction sites declines. So the amount of smoke it can combust becomes less and less until it cannot keep a high enough temp to keep the sustaining ration going.

So yes the efficiency of the cat degrades as in it can’t handle as much smoke. But hopefully you are running in a regime where you are never overloading the cat (it can happen). So your thermal efficiency (wood in to heat out) remains unchanged until the cat is really degraded and won’t light off.

In short cat efficiency doesn’t matter.

 

[John Lehet]

Sorry if I seemed grumpy in my response. No grumpiness at all around curiosity, wood stove geekiness, wanting the best efficiency. I’m all in on that! But ChatGPT, grrr. If it could give you solid references or draw out the line of research that led to its conclusions, that would be one thing. But it’s a black box that can be completely wrong, and you never know if it is. To use a crisis-causing amount of electricity to be able to do that. Well.

I decided on the hybrid pretty much because the specific stove I fell in love with happened to be a hybrid. Also it appeals to me that the catalyst gets a break if the stove can do secondary combustion. I’m not sure, but I think it will put on a prettier flame show. Some pure cat stoves, like the Woodstock Fireview apparently put on a nice flame show. My impression is that some other pure cat stoves, like Blaze King, can spend a lot more time looking like a pure black box (with the trade off of even longer clean-burn times).

So (as many readers of this forum are probably tired of hearing), I’m getting (I hope, if they can ever ship it) a Woodstock Progress Hybrid. I picked that stove because so many people seem to like it 100%, and there are few if any complaints about it online. By all accounts it can easily hold a fire overnight, which is a feature I’ve been living without. I wake up to a struggling mini split and a cold room, once it’s real winter. The manufacturer is nearby, so I could see it in person. It’s lovely, efficient, it seems all around good. A unicorn stove.

 

[brenndatomu]

Seems like a good convo to involve @Highbeam in.

 

[Fargo]

Sorry if I seemed grumpy in my response. No grumpiness at all around curiosity, wood stove geekiness, wanting the best efficiency. I’m all in on that! But ChatGPT, grrr. If it could give you solid references or draw out the line of research that led to its conclusions, that would be one thing. But it’s a black box that can be completely wrong, and you never know if it is. To use a crisis-causing amount of electricity to be able to do that. Well.

Trust me I get it. I'm actually the same way. For all the hype it gets, its insane how poor the answers can be. But even more bewildering is how much big tech is pushing it, considering how much energy AI consumes. It seems severely hypocritical to me for any company promoting the use of AI to claim they are environmentally friendly. It obviously has a lot of potential revenue streams though. Otherwise, it wouldn't be promoted like it is.

But yes, I do use it on occasion. I do try to follow up the data sources it provides, because as you pointed out it is notorious for fabricating information or simply taking things out of context. On the efficiency of a woodstove cat though, I'm just not finding much info. Some of the links from chatgpt point to a document from Cal/EPA Resource board. But the document is pretty sparce. Only saying that cat efficiency does drop over time. So I'm not sure. Another search pointed to a more indepth document. I think the links should be included here. It might be worth my reading rather than trusting the AI

Chatgpt says

• The EPA’s “Residential Wood Combustion Technology Review” notes that “with normal use … emissions of particles from most catalytic wood stoves will increase, in some cases reaching conventional stove levels within five years of use due to the loss of catalytic activity.” EPA+1
• In that same review, the authors show “default” (new) efficiencies of about 72% for catalytic stoves, compared with 68% for non-catalytic. EPA+1
  

So in short, I agree chatgpt is not the best research tool. But it can help to find documents.

 

[EbS-P]

Trust me I get it. I'm actually the same way. For all the hype it gets, its insane how poor the answers can be. But even more bewildering is how much big tech is pushing it, considering how much energy AI consumes. It seems severely hypocritical to me for any company promoting the use of AI to claim they are environmentally friendly. It obviously has a lot of potential revenue streams though. Otherwise, it wouldn't be promoted like it is.

But yes, I do use it on occasion. I do try to follow up the data sources it provides, because as you pointed out it is notorious for fabricating information or simply taking things out of context. On the efficiency of a woodstove cat though, I'm just not finding much info. Some of the links from chatgpt point to a document from Cal/EPA Resource board. But the document is pretty sparce. Only saying that cat efficiency does drop over time. So I'm not sure. Another search pointed to a more indepth document. I think the links should be included here. It might be worth my reading rather than trusting the AI

Chatgpt says

• The EPA’s “Residential Wood Combustion Technology Review” notes that “with normal use … emissions of particles from most catalytic wood stoves will increase, in some cases reaching conventional stove levels within five years of use due to the loss of catalytic activity.” EPA+1
• In that same review, the authors show “default” (new) efficiencies of about 72% for catalytic stoves, compared with 68% for non-catalytic. EPA+1

So in short, I agree chatgpt is not the best research tool. But it can help to find documents.

First link is from 1998. Doesn’t mean it bad just dated. Anyone using a household appliance from the late 90s.? Technology has moved on especially since EPA changed emissions regulations about that time.

Testing protocols matter a lot. Just figure 5+- % and those stoves are the same.

What till matter more and save more wood is insulation and air sealing.

 

[John Lehet]

What till matter more and save more wood is insulation and air sealing

In my case, I’m in an 1860s building. First thing we did (well, it took several months and we were well into winter), we dropped $12k+ on insulation and sealing. I had a crew here who had a bit of time between jobs, so they were willing to sleuth, found some really interesting stuff to work on. Sealed the stone foundation crawlspace with foam, put in a lot of cellulose where they could. Still, in the end, the blower door test — not sure how much better that was. We could feel huge difference in real time while they were working on it. In the end it’s still an 1860s building with a thermal face lift. Why I need a wood stove. And efficiency is good.

 

[Highbeam]

Seems like a good convo to involve @Highbeam in.

Actually, on this one especially, the man who has actually tested efficiency would be an excellent resource @BKVP. I seem to remember that testing is done on a "seasoned" catalyst.

I believe it is a false assumption that catalyst efficiency drops a fixed amount each year until death. In my experience the catalyst works perfectly until it dies and it dies in a spectacular fashion. L:ike in a car. There is a brief honeymoon period when a new cat works extra super well and then a long 10,000+ hours of dependable, efficient, excellent performance, and then bam it dies with smokey chimney, tar dripping, inability to maintain cat temperature at low settings, and higher thermostat settings required to heat the home. All easily fixed by a 200$ cat swap in about the same amount of time it takes to change your shoes. I get 2-3 years per catalyst but I burn at low settings almost all of the time and my burning season can be 9 months long so at least 10k hours per cat. I'm happy with that.

I have actually burned a modern noncat and a modern cat stove on the same hearth with the same fuel for many years each and I found much higher efficiency with the cat stove. I burn 20% less, 4 cords vs. 5 per year with the noncat.

Nothing wrong with a noncat but they are all going to be less efficient than the leader of the pack BK.

 

[Sim]

Actually, on this one especially, the man who has actually tested efficiency would be an excellent resource @BKVP. I seem to remember that testing is done on a "seasoned" catalyst.

I believe it is a false assumption that catalyst efficiency drops a fixed amount each year until death. In my experience the catalyst works perfectly until it dies and it dies in a spectacular fashion. L:ike in a car. There is a brief honeymoon period when a new cat works extra super well and then a long 10,000+ hours of dependable, efficient, excellent performance, and then bam it dies with smokey chimney, tar dripping, inability to maintain cat temperature at low settings, and higher thermostat settings required to heat the home. All easily fixed by a 200$ cat swap in about the same amount of time it takes to change your shoes. I get 2-3 years per catalyst but I burn at low settings almost all of the time and my burning season can be 9 months long so at least 10k hours per cat. I'm happy with that.

I have actually burned a modern noncat and a modern cat stove on the same hearth with the same fuel for many years each and I found much higher efficiency with the cat stove. I burn 20% less, 4 cords vs. 5 per year with the noncat.

Nothing wrong with a noncat but they are all going to be less efficient than the leader of the pack BK.

I've been reading a few people mention a cat lasts between 10000-12000 hours. However I've noticed different stoves have different size cats. Some very small and others larger. Is it not dependent on the size of the cat? Also how does the hours change when the stove also includes secondary burn tubes? Does that estimated 10-12k hours go up?

 

[Fargo]

Actually, on this one especially, the man who has actually tested efficiency would be an excellent resource @BKVP. I seem to remember that testing is done on a "seasoned" catalyst.

I believe it is a false assumption that catalyst efficiency drops a fixed amount each year until death. In my experience the catalyst works perfectly until it dies and it dies in a spectacular fashion. L:ike in a car. There is a brief honeymoon period when a new cat works extra super well and then a long 10,000+ hours of dependable, efficient, excellent performance, and then bam it dies with smokey chimney, tar dripping, inability to maintain cat temperature at low settings, and higher thermostat settings required to heat the home. All easily fixed by a 200$ cat swap in about the same amount of time it takes to change your shoes. I get 2-3 years per catalyst but I burn at low settings almost all of the time and my burning season can be 9 months long so at least 10k hours per cat. I'm happy with that.

I have actually burned a modern noncat and a modern cat stove on the same hearth with the same fuel for many years each and I found much higher efficiency with the cat stove. I burn 20% less, 4 cords vs. 5 per year with the noncat.

Nothing wrong with a noncat but they are all going to be less efficient than the leader of the pack BK.

I thought about calling out to BKVP, but I didn't want to bother him as I was just musing how the efficiency of a cat will deteriorate with age. But it would be great if he could share some insight.

It might very well be a false assumption that modern cats loose efficiency... or at least enough to matter. I already shared my source for that info and its know to be notoriously unreliable (chatgpt).

 

[BKVP]

Very interesting stuff. First and foremost, cataltyic AND secondary combustion stoves drop in emissions reduction efficacy.

The aged cat stove emissions at 5 years is compared to a new secondary combustion stoves. It is also the cleanest secondary combustion stove at the time. I know this because we paid $25k as our share of the study.

Next, the life span average....this is candidly BS. This is like saying all tires are good for 40k miles. Cat placement, threshold temperatures, user interface, fuel and so much more effects combustor lifespan.

The aged cats studied in the study showed that after 9+ seasons, the average cat was 1 gr/h dirtier than new. At the time of the study, the aged cats were still cleaner burning at 9 years of age than 84% of the secondary stoves listed by EPA.

All emissions testing ON ALL COMBUSTION designs requires 50 hours of conditioning PRIOR to testing. Prior to 2015' EPA NSPS, only cataltyic models required conditioning. After many trips to EPA's RTP location and meetings there, EPA was convinced that conditioning is a requirement of all solid fuel heaters.

BKVP

 

[Murray01]

Three year warranty, no charge, not bad IMHO. I did fill out a separate mail in card for a 10 year warranty on the CAT, don’t remember the details unfortunately.