What should I be expecting - first Cat Stove

[joefrompa]

Hi all:

I need some expectation setting from the wisdom of the group. My first and only prior wood burning stove was a Lopi 1750 insert, which I used for 12 winters (flawlessly I may add - that stove needed nothing but a single new door gasket in 12 years of burning). In that stove, I could shove it to the brim with some oak or similar, get it roaring very hot, turn the air down low, and 8 hours later I'd have a bed of coals and maybe a 200-250 degree stove. Sometimes the fan would still be blowing, sometimes not - so basically it had a max 8 hour burn time. So that's my background

I just built a new home and designed my home from scratch around a free-standing wood burning stove. I built the chimney inside the house envelope and almost achieved a perfect straight vertical chimney. And I bought a Hearthstone Green Mountain 60, my first cat stove on a 2.0 cubic foot firebox. Hearthstone claims a 24 hour "heatlife" when burning a full firebox in ideal conditions.

However, I'm not really seeing differences when I use the cat. Maybe some slower burning, but I need some expectation setting in two ways:

1. When I engage the cat, the fire looks the same. It doesn't slow down, or burn differently in any meaningful way. Is that correct?

2. I'm about ~5-6 fires in now and learning the stove. Last night I had a roaring fire going with the cat fully heated and the temp solidly in the mid-range of cat heat target temps, shoved big pieces of hardwood on top, re-engaged the cat, and had the air a fraction of an inch away from fully closed. 8 hours later I had....a bed of coals and the blower was still on for maybe 30 more minutes. The temp gauge was no longer in the cat range, though it was pretty darn close. It really didn't perform notably different than what I'd experience from a non-cat stove.

Am I anticipating the wrong things from a cat? Is this about right but maybe it would just keep humming at ~200 degrees for many hours on that bed of coals with no visible activity I can see?

Thanks all,

Joe

 

[bholler]

Hi all:

I need some expectation setting from the wisdom of the group. My first and only prior wood burning stove was a Lopi 1750 insert, which I used for 12 winters (flawlessly I may add - that stove needed nothing but a single new door gasket in 12 years of burning). In that stove, I could shove it to the brim with some oak or similar, get it roaring very hot, turn the air down low, and 8 hours later I'd have a bed of coals and maybe a 200-250 degree stove. Sometimes the fan would still be blowing, sometimes not - so basically it had a max 8 hour burn time. So that's my background

I just built a new home and designed my home from scratch around a free-standing wood burning stove. I built the chimney inside the house envelope and almost achieved a perfect straight vertical chimney. And I bought a Hearthstone Green Mountain 60, my first cat stove on a 2.0 cubic foot firebox. Hearthstone claims a 24 hour "heatlife" when burning a full firebox in ideal conditions.

However, I'm not really seeing differences when I use the cat. Maybe some slower burning, but I need some expectation setting in two ways:

1. When I engage the cat, the fire looks the same. It doesn't slow down, or burn differently in any meaningful way. Is that correct?

2. I'm about ~5-6 fires in now and learning the stove. Last night I had a roaring fire going with the cat fully heated and the temp solidly in the mid-range of cat heat target temps, shoved big pieces of hardwood on top, re-engaged the cat, and had the air a fraction of an inch away from fully closed. 8 hours later I had....a bed of coals and the blower was still on for maybe 30 more minutes. The temp gauge was no longer in the cat range, though it was pretty darn close. It really didn't perform notably different than what I'd experience from a non-cat stove.

Am I anticipating the wrong things from a cat? Is this about right but maybe it would just keep humming at ~200 degrees for many hours on that bed of coals with no visible activity I can see?

Thanks all,

Joe

A cat doesn't magically give you longer burn times. What it does do is allow you to shut the air down further and still burn cleanly. How tall is your chimney?

 

[joefrompa]

A cat doesn't magically give you longer burn times. What it does do is allow you to shut the air down further and still burn cleanly. How tall is your chimney?

Chimney's ~30 feet tall.

You raise an interesting point. I guess I should experiment more with shutting the air down all the way as long as the temp is in the "Cat engage" mode. Previously, if I saw that smothering the fire, I wouldn't do it. But here what you are saying is it can be smothered to some degree and still burn cleanly with the cat - leading to the longer burn times/slower wood consumption.

 

[Ashful]

You’re on the right path. Just two more notes:

1. With 30 feet of pipe pulling on the thing, even shutting down fully may still allow enough air to prevent your stove from achieving its maximum burn times. A key damper is often recommended on pipes this tall, to optimize performance.

2. When shutting down real low from a raging fire, esp if you install that key damper, do it in two or more steps spaced a few minutes apart. In all cat stoves this will help to avoid spiking the cat temp, and with short pipes or key dampers, it can also help to prevent any back puffing.

 

[Highbeam]

That's a good looking stove, I hope it performs per the marketing for you. I had a modern hearthstone noncat stone stove for many years before moving to a plate steel stove that's much less pretty but really does provide that 24 hours of heat that I wanted. Not all cat stoves are created equal.

 

[NYSB]

I have a cat stove, Regency CI2700 insert mentioned above with the broken screw…. That minor issue aside, it’s a great stove. They claim it is a “hybrid” stove - it has both a cat and some secondary air tubes to promote re-burning of secondary gasses in the firebox as well. We have a family member in a nearby town who has a non-cat stove. For his non-cat stove it seems to run more efficiently when really hot - you can really see those secondary flames. When he runs it with less air, it smolders and doesn’t burn as much of the secondary gasses. You can tell by the smoke it emits.

Meanwhile our cat stove runs efficiently at high burn rates and also runs efficiently at low burn rates. At those low burn rates I see just a few very gentle flames, and a few secondaries, in the fire box. But the cat will glow red for hours, indicating secondary combustion is occurring. From the chimney is those conditions I just see some whisps of white steam being emitted - hardly any smoke.

The firebox on this stove is about 2.6 cbft and I can get burn times 16-18 hrs before I feel like I need to reload. After 24 hrs there are still enough coals to quickly get it going again, but not much heat getting put out. When re-loading on a nice bed of coals I pack it to the gills. I try to leave minimal space left over. I leave the door open a bit and/or open the air control all the way. Once there are substantial flames going I close the door and begin to turn down the air supply in stages, over about 10-30 minutes. Once the cat reaches 600deg I engage it. I continue turning down the air control. On most long winter nights i will turn the air control down about 4/5ths of the way and just leave it with the circulating fan on high. This keeps our whole house (2000sqft) warm the whole night. After about 12- 14 hours I refill the stove and repeat. If I turn down the air control all the way it’ll go 18+ hours. After that, I notice chunks of charcoal left over…that’s probably not quite enough air for complete combustion I suppose.

I think both cat and non-cat stoves can be run efficiently .

And of course the dryer and denser the wood the better burn times you’ll get.

Good luck.

SB

 

[jalmondale]

Chimney's ~30 feet tall.

You raise an interesting point. I guess I should experiment more with shutting the air down all the way as long as the temp is in the "Cat engage" mode. Previously, if I saw that smothering the fire, I wouldn't do it. But here what you are saying is it can be smothered to some degree and still burn cleanly with the cat - leading to the longer burn times/slower wood consumption.

Exactly. A cat stove on low may not have any visible flames at all, but because the cat can combust the exhaust (and keep its own temperature up by doing so), all that smoky particulate is still being burned efficiently.

That said, the 'heat life' fine print suggests you won't actually get that long of a burn - I have a cat stove that can do a 10 hour burn on a 1.85 cu ft firebox, but it still has embers that could relight things 14 hours later (the HeatLife definition is "Under the right conditions, you will be able to start a new fire with kindling up to the end of the product’s HeatLife"). So I'd expect you could get 17 hours of useful heat running on low off something with a HeatLife of 24 hours.

 

[tabner]

i am on my second year of heating with a Green Mountain 60. My experience has been similar to what you describe. I think it's important to distinguish between a Cat stove and a Cat stove. Or that is to say, a Catalytic Stove, and a stove that has a Catalyst in it. The GM60, in my opinion, is just a secondary burn/tube stove, with Cats installed as a scrubber for an EPA benefit.
6 hours of good strong heat. with 2 to 3 hours of nice warm stove afterwards, is the best i have achieved. I can relight on coals (slowly with a bit of kindling) in the morning. There have been times when i shut the air down a bit too much, or too quick, and the flame snuffs out, resulting in glowing orange cats. Which i guess is a nice benefit of the Hybrid Cat system on these stoves - rather than smoking out smog and pollution and gunking up the chimney, the cats are scrubbing that smoke. But i don't think it's really heating well when it's burning that way.
better to run the GM60 like a non-cat stove, and just think of the cats as a bit of extra insurance.

 

[bholler]

i am on my second year of heating with a Green Mountain 60. My experience has been similar to what you describe. I think it's important to distinguish between a Cat stove and a Cat stove. Or that is to say, a Catalytic Stove, and a stove that has a Catalyst in it. The GM60, in my opinion, is just a secondary burn/tube stove, with Cats installed as a scrubber for an EPA benefit.
6 hours of good strong heat. with 2 to 3 hours of nice warm stove afterwards, is the best i have achieved. I can relight on coals (slowly with a bit of kindling) in the morning. There have been times when i shut the air down a bit too much, or too quick, and the flame snuffs out, resulting in glowing orange cats. Which i guess is a nice benefit of the Hybrid Cat system on these stoves - rather than smoking out smog and pollution and gunking up the chimney, the cats are scrubbing that smoke. But i don't think it's really heating well when it's burning that way.
better to run the GM60 like a non-cat stove, and just think of the cats as a bit of extra insurance.

Very good description but you are missing the fact that in and stove with a cat (hybrid or not) the heat output is very low when you have no flames just a glowing cat. That's how they get such long burn times with the same amount of wood.

 

[Ashful]

You can consume a load of wood in 6 hours, or stretch it for 30 hours, in my BK Ashfords. But it's the same 700k BTU of oak in the box, and the same 500k BTU going into your house, either way.

Whether that 500k BTU is enough to heat your home for 6 hours or 30, under the given weather conditions, has nothing to do with the stove from which it is coming.

 

[Highbeam]

You can consume a load of wood in 6 hours, or stretch it for 30 hours, in my BK Ashfords. But it's the same 700k BTU of oak in the box, and the same 500k BTU going into your house, either way.

Whether that 500k BTU is enough to heat your home for 6 hours or 30, under the given weather conditions, has nothing to do with the stove from which it is coming.

Correct, burn time is just a matter of how you choose to operate your stove. It could be out in a field. The output from my cat stove on low is lots of heat, enough to heat my home 95% of the time. It can burn hotter if I needed way more heat and a shorter burn time would result.

The home and the home's heat demands do not determine burn time.

 

[bholler]

The home and the home's heat demands do not determine burn time.

If you actually want to heat the house it absolutely does. You can run on low most of the time. I almost never can. So my burn times are far lower than yours with the same stove

 

[Diabel]

If you actually want to heat the house it absolutely does. You can run on low most of the time. I almost never can. So my burn times are far lower than yours with the same stove

Time to start sealing your house😝

 

[bholler]

Time to start sealing your house😝

Or move it off the top of a ridge. It's sealed pretty well just lots of wind all the time

 

[Diabel]

Or move it off the top of a ridge. It's sealed pretty well just lots of wind all the time

If it only was that easy. Resealing the attic and re insulating it is the best $$ and time spent.

 

[Highbeam]

If you actually want to heat the house it absolutely does. You can run on low most of the time. I almost never can. So my burn times are far lower than yours with the same stove

I disagree. Any wood burned heats the house. Just maybe not enough to keep your house comfortable. Think physics. Think conservation of energy. You choose a higher burn rate not the house. The higher burn rate you choose results in a shorter burn time.

I of course understand your mistake. You think that in order to hold the house temperature constant with the stove that it must be burned harder when the weather is colder but that’s a choice. You did not have to make that choice. Especially if you’re like most folks that also use a furnace.

 

[bholler]

If it only was that easy. Resealing the attic and re insulating it is the best $$ and time spent.

I have already spent allot of time and money found that

 

[bholler]

I disagree. Any wood burned heats the house. Just maybe not enough to keep your house comfortable. Think physics. Think conservation of energy. You choose a higher burn rate not the house. The higher burn rate you choose results in a shorter burn time.

I of course understand your mistake. You think that in order to hold the house temperature constant with the stove that it must be burned harder when the weather is colder but that’s a choice. You did not have to make that choice. Especially if you’re like most folks that also use a furnace.

Yes of course I choose a higher burn rate because the house needs more BTUs. Which make the load of wood in my stove burn up faster.

I suppose how much wood I load in the stove doesn't change burn time either because that's a choice. Same with species of wood right? What about chimney height? Outside temp etc etc.

You are right the maximum potential burn time doesn't change. But my concern is with burn times while heating my home. I don't care about maximum potential times at all.

 

[Ashful]

Who's on first?

 

[Ashful]

Here's a recent post to another thread that seems fitting, here:

Getting close to the Sirocco 20 not keeping up with the weather with 12 hour burns. Been getting into the teens at night and barely into the 20's during the day. Heading for single digits by the end of the week. Downstairs dropped to 65° this morning and upstairs was 70°. Went ahead and turned the boiler thermostats up to 65° but I've been enjoying the new woodstove so much that I may start doing a small load in the evening and full load for the night and morning. I was set on 12 hour burns and letting the boiler pick up the slack but now I figure why do that when cutting, splitting and burning is so much fun 😊

 

[Highbeam]

Yes of course I choose a higher burn rate because the house needs more BTUs. You are right the maximum potential burn time doesn't change. But my concern is with burn times while heating my home. I don't care about maximum potential times at all.

You’re right, potential burn time doesn’t change. The operator sets the burn rate. All of our stoves have output controls and we can set the burn rate to whatever we want. Not everybody is trying to heat 100% of their home with their stoves, some (I predict most)choose burn rates that work with their schedule and let the furnace pick up the slack so burn time is independent of house demand. Isn’t that how @Ashful runs his? I’m certainly doing some of that with my new heat pump to share duties.

I'll tell you what, if it hurts your feeling less, how about lets just say I have different way of looking at it. I understand your theory about why you think you have no control over your burn rate but I have my own theory about why my knob works!

 

[Ashful]

...some choose burn rates that work with their schedule and let the furnace pick up the slack so burn time is independent of house demand. Isn’t that how @Ashful runs his?

Yes. But I could be convinced to give it another go at doing solely wood, if you're offering to come help me fell, haul, split, stack, move, and load enough fire wood to heat 6700 sq.ft. of 18th century construction in an eastern PA climate. Bring gloves!

 

[stoveliker]

A stove has a certain fixed range of output - due to its engineering design. Cat stoves often (not always) have extended that output range to the lower end as compared to stoves that are similar but don't have a cat.

Output is just the rate of BTU release from the (fixed) amount of BTUs in a (full) firebox.

Output rate is set by the user via the air control.

The user sets that output rate taking into account the wanted temperature in the home. And the rate to reach that temperature is affected by the heat loss rate of the home.

It's simple as that.
Boundary conditions, part of which are "mechanical" (heat loss rate of the home) and part of which are "personal" (I want 68 F, others want 72 F etc.), determine in practice the heat output rate that a user sets on a stove (within the mechanical limits dictated by the stove design).

A discussion on WHICH boundary condition (mechanical or personal) is the bottleneck, is not useful imo.


To the OP: your post #3 is correct.

 

[Highbeam]

A stove has a certain fixed range of output - due to its engineering design. Cat stoves often (not always) have extended that output range to the lower end as compared to stoves that are similar but don't have a cat.

Output is just the rate of BTU release from the (fixed) amount of BTUs in a (full) firebox.

Output rate is set by the user via the air control.

The user sets that output rate taking into account the wanted temperature in the home. And the rate to reach that temperature is affected by the heat loss rate of the home.

It's simple as that.
Boundary conditions, part of which are "mechanical" (heat loss rate of the home) and part of which are "personal" (I want 68 F, others want 72 F etc.), determine in practice the heat output rate that a user sets on a stove (within the mechanical limits dictated by the stove design).

A discussion on WHICH boundary condition (mechanical or personal) is the bottleneck, is not useful imo.


To the OP: your post #3 is correct.

Thank you for saying it more eloquently than I could.

Every breath you take, every candle you burn, every stick of wood you burn "heats your house" to some extent.

 

[stoveliker]

That is the first time I've been accused of eloquency...

To dispel that myth: every fart heats my house too.

Sometimes it's useful to read a discussion of others to distill something in a clear way for myself. And given that my memory is far from perfect, I tend to write it down.