Lazy Cat?

[stoveliker]

Newcomer here trying to learn. I thought you want to keep the bypass open as little as possible when cat is in the active zone. Is it damaging to the cat to run the stove with the bypass open (in which case I'd be much quicker to open and close the bypass during hot reload)? Or it's just for efficiency sake?

It sounds like a balance between two opposite needs:
- Keep the cat closed whenever the cat is in active temp zone (for efficiency? to avoid damage?)
- Open the bypass for a few minutes before and after hot reloads
but I might be misunderstanding something

If the cat is (well) within the active zone, I reload (of course with the bypass open), close the main door, let it go for a minute or so to get the cool room air out of the firebox (while the new load is already burning well - it's dry and the air is fully open), and then immediately close the bypass.

It is *not* damaging to the cat to run with the bypass open. It might be damaging to the stove (mostly bypass area) to do so too long, as it gets hotter that way than when burning with the bypass closed.

 

[Woody Stover]

If the cat is (well) within the active zone, I reload (of course with the bypass open), close the main door, let it go for a minute or so to get the cool room air out of the firebox (while the new load is already burning well - it's dry and the air is fully open), and then immediately close the bypass.

It is *not* damaging to the cat to run with the bypass open. It might be damaging to the stove (mostly bypass area) to do so too long, as it gets hotter that way than when burning with the bypass closed.

I usually burn in a new load a bit longer than a minute, since the initial moisture coming off the new wood will probably slow the cat a bit at first anyway. I like to see that cat glowing shortly after I close the bypass, so that I minimize the amount of unburned smoke through the cat. Of course that'll also depend on the wood--If it's super-dry, or lighter species that catch and gas fairly quickly, I won't need to burn in the new load as long.
Right, you don't have to worry about damaging the stove when running with the bypass open, as long as the fire in the box isn't too vigorous--you don't want a roaring blaze in there concentrating excessive flame heat around the bypass opening.

 

[stoveliker]

I usually burn in a new load a bit longer than a minute, since the initial moisture coming off the new wood will probably slow the cat a bit at first anyway.

I don't think moisture (vapor) per se slows a cat. Low temperature does. (Of course evaporating water eats energy, so the temperature will be lower.)

I like to see that cat glowing shortly after I close the bypass,

If my cat was well in the active regime before I opened to reload, then once I have decent flame - which happens within a minute - the cat glows immediately when I close the bypass and have the air fully open. This may depend on the stove design (the air flow in the firebox), as it will depend on how much heat is transported to the cat versus radiated out into the stove walls and room before reaching the cat.
I do rake my coals to the front before reloading, and this results (for my stove) in the first flame upon reloading being vigorous because the airwash goes directly to where the new wood touches the coals, and it results in the flames going straight up towards the flameshield before the cat.

so that I minimize the amount of unburned smoke through the cat. Of course that'll also depend on the wood--If it's super-dry, or lighter species that catch and gas fairly quickly, I won't need to burn in the new load as long.

This works for me with (red) oak, or pine, either way.

Right, you don't have to worry about damaging the stove when running with the bypass open, as long as the fire in the box isn't too vigorous--you don't want a roaring blaze in there concentrating excessive flame heat around the bypass opening.

Yes, well-said.

 

[Highbeam]

I have indeed melted a few steelcats, all the cheaper diesel foil variety (Condar), and all in pretty crappy stoves (Jotul Firelight 12's). They distort somewhere above 2600F (yes... been there), but I've never seen one crack. How is that even possible? You'd have to reach a metal fatigue threshold through numerous CTE-driven cycles seems unlikely anyone would keep a cat installed and in use after such distortion.

The welds break. The layers of cells slide apart from each other. I was unimpressed with the metal cat's longevity, it died/wore out much faster than ceramics, and of course the small holes plug up. I think manufacturers mostly started using them because they light off slightly earlier to give some slight emissions edge but more because they don't crack/break/crumble so are less likely to be warranty claims.

The cat that BK would recommend is the one that comes with the original stove - they can't (legally) recommend anything else as the testing and certification happened with that OEM cat.

Supposedly the king and princess are tested/approved with both ceramic and steel so you have a choice. Since the princess cat is the same size as the 30box cat you appear to have a choice there too but without an official declaration of choice from BK.

 

[Ashful]

The welds break. The layers of cells slide apart from each other. I was unimpressed with the metal cat's longevity, it died/wore out much faster than ceramics, and of course the small holes plug up.

Even at normal temperatures? I've run a combined 11 years on three steelcats, between my two Ashfords, and not had any mechanical issues with any of them. All of my steelcat failures were due to stupid-high cat temperatures in the Jotuls.

It's curious that all of the steelcats seem to have smaller passages than the ceramic cats, with the diesel foil ones being the most densely-corrugated, and the durafoil being only slightly coarser than that. I guess the marketing is all centered on their superior surface area, permitted by the thinner substrate, but as noted... clogging.

A coarse steelcat would have the CTE durability advantage, without being so prone to clogging. Maybe it's not as marketable, not having the obvious surface area advantage,

 

[stoveliker]

The surface area is not dependent much on the thickness of the foil, but more on the (roughness of the coating and the) folding pattern of the steel foil.

And that (folding pattern) is easily tunable. So in principle clogging could easily be avoided by creating larger channels.

The fact that that has not been done makes me wonder if the *areal* performance is exactly the same for a steel cat and a ceramic one, given the (obvious) difference in exposed surface area (that has to be multiplied by a factor pertaining to the the wash coating roughness).
Given the larger (I think) surface area of the steel ones, maybe they are actually less efficient thus needing the larger area (and narrower "gas tubes", leading to more frequent collisions of gases with the surface) to reach the same emissions level?

Or BK went to steel cats for the latest 30 boxes because the boxes have higher emissions and the steel ones with their larger surface area cut that down to EPA acceptable levels.

But obviously this enters the realm of trade secrets, so we won't get an answer

 

[Highbeam]

Even at normal temperatures? I've run a combined 11 years on three steelcats, between my two Ashfords, and not had any mechanical issues with any of them. All of my steelcat failures were due to stupid-high cat temperatures in the Jotuls.

It's curious that all of the steelcats seem to have smaller passages than the ceramic cats, with the diesel foil ones being the most densely-corrugated, and the durafoil being only slightly coarser than that. I guess the marketing is all centered on their superior surface area, permitted by the thinner substrate, but as noted... clogging.

A coarse steelcat would have the CTE durability advantage, without being so prone to clogging. Maybe it's not as marketable, not having the obvious surface area advantage,

Of course at normal temperatures, we’re all running BKs.

 

[Ashful]

The surface area is not dependent much on the thickness of the foil, but more on the (roughness of the coating and the) folding pattern of the steel foil.

I was referring to the higher cell count per square inch of steelcats, versus ceramic.

Of course at normal temperatures, we’re all running BKs.

Well, yes... today. But not always! All of my cat torture (pun intended) happened in the stoves I owned before these BK's.

 

[stoveliker]

I was referring to the higher cell count per square inch of steelcats, versus ceramic.

Hm, either I need to see a doctor or a post was edited, because my memory swears that someone used "thickness of the foil" in one of their posts, which resulted in my remark.

 

[Ashful]

Hm, either I need to see a doctor or a post was edited, because my memory swears that someone used "thickness of the foil" in one of their posts, which resulted in my remark.

My wife likes to yell at me for things I never said.

Me: "I never said that."
Her: "But I know that's what you meant."
Me: "No, what I meant is what I said."
Her: "Jerk."

 

[stoveliker]

Thanks for telling me I need to see a doctor
(no worries, just joking)