Please help me understand new/hyperactive cats

[BKVP]

Fascinating discussion. I'm one of those happy, but nervous new owners. On my Ashford 25 [8-10 burns so far; 15-20% mc Oak, longerish straight flue draft of 18-22 feet]. I notice that turning down the Tstat to lowest setting often bumps needle higher [1 o'clock position or 40-45 % into the red/active range on the gauge] and pushes higher heat out of the maxed fan [from 325F to 400F] .

I'm burning without a flue sensor in a tighter masonry/brick fireplace [just fits] and with blockoff plate.

The nervous point comes from the fact that Temp goes UP, even when thermostat setting is at LOWEST possible setting [cat is full glowing yellow, and primary flames are not extinguished.] Ergo, nothing in the manual to reduce temps at that point - even if I wanted to.

Q: Aside from the question of potential cat damage, safety. Should I be concerned about potential damage to or melting of flue pipe at the collar when the cat is "hyper active" ? How would I know and when or under what conditions I should be concerned?

Thanks!

This is absolutely what should happen. As you slow incoming combustion air, the residence time in the combustor increases which results in higher temps. It is why catalytic stove burn cleaner as you go lower. Secondary stove burn cleanest on high because they destroy particulate thermally as opposed to chemically.

This is an inverse relationship.

BKVP

 

[fao1989]

This is absolutely what should happen. As you slow incoming combustion air, the residence time in the combustor increases which results in higher temps. It is why catalytic stove burn cleaner as you go lower. Secondary stove burn cleanest on high because they destroy particulate thermally as opposed to chemically.

This is an inverse relationship.

BKVP

Thanks BKVP. Still trying to completely understand this:
Makes sense that hot cat and slow air burns more thoroughly and cleaner. But also evidently, a lot hotter.

So Turning the A25 Tstat lower [counterclockwise] actually increases stove temperature as air flow decreases volume and velocity across the cat [increased fuel residence time]?

This begs two other questions:

1. How does one then down-regulate temperature once the cat is fully active and Tstat is already at minimal/lowest setting? Do I open the throttle [clockwise], add air flow [decrease fuel residence time in cat] and increase primary burn flames ?

I'm confused, - thats definitely an inverse relationship - but it seems to run counter to the manual, page 21:
"A HIGH(wide line) thermostat setting will produce maximum heat which is more than suitable for heating the average size home."

Or am I simply stuck with a hot cat and stove once the Tstat is minimized lowest [counterclockwise], until fuel fumes/off-gasing decreases...?

2. If CAT is active and Tstat is turned down [low position on page 21], when, if ever, should I be concerned with collar exit temps, when the cat is 'hyperactive' and brightly glowing? Recall, I dont have a flue temp probe, yet. In unlikely case of a flue fire, how would you cool/slow the stove further?

By the way, I took thermodynamics twice at a Service Academy 30 years ago. Flunked the first time, passed on the second attempt. So type your reply slowly for me....lol.

Thanks for your patience!

 

[BKVP]

Thanks BKVP. Still trying to completely understand this:
Makes sense that hot cat and slow air burns more thoroughly and cleaner. But also evidently, a lot hotter.

So Turning the A25 Tstat lower [counterclockwise] actually increases stove temperature as air flow decreases volume and velocity across the cat [increased fuel residence time]?

This begs two other questions:

1. How does one then down-regulate temperature once the cat is fully active and Tstat is already at minimal/lowest setting? Do I open the throttle [clockwise], add air flow [decrease fuel residence time in cat] and increase primary burn flames ?

I'm confused, - thats definitely an inverse relationship - but it seems to run counter to the manual, page 21:
"A HIGH(wide line) thermostat setting will produce maximum heat which is more than suitable for heating the average size home."

Or am I simply stuck with a hot cat and stove once the Tstat is minimized lowest [counterclockwise], until fuel fumes/off-gasing decreases...?

2. If CAT is active and Tstat is turned down [low position on page 21], when, if ever, should I be concerned with collar exit temps, when the cat is 'hyperactive' and brightly glowing? Recall, I dont have a flue temp probe, yet. In unlikely case of a flue fire, how would you cool/slow the stove further?

By the way, I took thermodynamics twice at a Service Academy 30 years ago. Flunked the first time, passed on the second attempt. So type your reply slowly for me....lol.

Thanks for your patience!

You're confusing stove temp with cat temp. If you take an IR gun and measure directly above the cat (hard to do on inserts like AF25) you will find very high surface temps on low burns, but as you move away, surface temps drop quickly.

Do the same thing on a high burn, and the surface areas get closer to temp above combustor.

BKVP

 

[fao1989]

You're confusing stove temp with cat temp. If you take an IR gun and measure directly above the cat (hard to do on inserts like AF25) you will find very high surface temps on low burns, but as you move away, surface temps drop quickly.

Do the same thing on a high burn, and the surface areas get closer to temp above combustor.

BKVP

Ah...Thank you. That now makes it understandable. Also explains why hot burns are recommended occasionally to burn creosote on the glass and interior walls, and why it builds up on slow burns.

In either case, high WOT (stove hot) or low (cat hotter) do I need to worry about collar and flue temps?
Or is my hyperviligance mirroring my 'hyperactive cat'?

 

[BKVP]

So long as you have a good quality liner and close bypass when active, you're covered....

BKVP

 

[fao1989]

Thank you.

 

[BKVP]

Merry Christmas and Happy Burning!

BKVP

 

[Highbeam]

So long as you have a good quality liner and close bypass when active, you're covered....

BKVP

Probably want to add "have a nice and tight door seal" to that list.

I often run low stove temps with a high cat temp. Black box mode but a glowing orange cat up top. That should be most efficient , cleanest, and lowest output for longest burn times.

 

[fao1989]

Probably want to add "have a nice and tight door seal" to that list.

I often run low stove temps with a high cat temp. Black box mode but a glowing orange cat up top. That should be most efficient , cleanest, and lowest output for longest burn times.

Thank you Highbeam.