Mansfield, First cat stove - operating questions

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ThisStoveIsOnFire

New Member
Sep 22, 2022
16
NH
I had the new Hearthstone Mansfield stove installed this year and have been running it for a week now, and have a couple questions for folks more experienced than I with operating cat stoves:

1. After reloading, is it ok to engage the catalyst right away if it’s well in the active range still, or do I need to wait 10-20 minutes first? The manual was a bit ambiguous, other than needing to run at a medium or high burn for that period of time.
2. On initial startup the stovepipe gets to 300 degrees, but after engaging the catalyst it consistently stays at 200. Is this expected because of the greater efficiency of the catalyst? Just want to make sure I shouldn’t be concerned about the pipe not being hot enough to prevent creosote from collecting.
 
For my stove the manual says to immediately engage the cat again after closing the door if it is still in the active zone. Dry wood is important though as cats don't like to eat relatively cold steam.

How do you measure your flue temp.
200 seems a bit cold to me. It's below the water condensation temperature. You don't want water dripping down in the chimney.
 
I have a magnetic thermometer on the pipe (which is single-wall) about 12" above the stove. I have not yet noticed any condensation other than a little moisture releasing from the soapstone as part of the break-in period.
 
Ok. I'm not sure you would notice the condensation by looking from the outside; if the pipe is installed correctly, it'd drip into the stove (if no elbows are present).

Is the thermometer reading correctly at room temperature? Do you have another way of checking the temperature to see that it is working well?

Cat stoves can indeed have low flue temps, but the general advice is to keep it above 250, especially this low in the flue; it'll cool down further up the flue. Water condensing is a good way to end up with creosote, as that water will capture smoke particles.

This is also why cat stoves do best with a double wall stove pipe; keep the already low gases from cooling down too much thru a single wall pipe.
 
200 degrees on single wall is probably around 400 degrees internal which is probably ok but on the low end. See any smoke out the chimney? That’s probably the best way to determine if the cat is working or has stalled. Is this a Woodstock stove?
 
It's a Hearthstone. It was a little dark outside this morning when I checked but it looked like some steam came out initially and then dissipated after a few minutes. Definitely nothing that looked like dark smoke.

The temperature on the cat is staying well within the active range and it's brand-new.

The run from the stove to the thimble is not ideal as there's not much rise before the elbow, which I'm assuming could be a factor?

IMG_1660.jpeg
 
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I had the new Hearthstone Mansfield stove installed this year and have been running it for a week now, and have a couple questions for folks more experienced than I with operating cat stoves:

1. After reloading, is it ok to engage the catalyst right away if it’s well in the active range still, or do I need to wait 10-20 minutes first? The manual was a bit ambiguous, other than needing to run at a medium or high burn for that period of time.

Back when all cats were ceramic, stove manuals used to always call for a period of letting the new load catch and dry, before closing the bypass and pushing a bunch of cold water vapor thru a hot combustor. After the popularization of steelcats, many stove manuals dropped this recommendation, as they're less prone to cracking due to thermal shock.

I'm still in the camp of letting the new load catch for 5 minutes in bypass, even if combustor is active, as the new load seems to catch more quickly and I never saw much point in jumping the gun.

2. On initial startup the stovepipe gets to 300 degrees, but after engaging the catalyst it consistently stays at 200. Is this expected because of the greater efficiency of the catalyst? Just want to make sure I shouldn’t be concerned about the pipe not being hot enough to prevent creosote from collecting.
Yes. Any concern with creo buildup is minimal, if properly functioning cat stays in active temperature range. A 200F pipe is no problem.

A few years from now, you will begin to see creosote build-up, even when cat is kept in active range. That will be your sign it's time to replace the thing, if you didn't notice other signs prior to that (eg. increased smoke output).
 
200 degrees on single wall is probably around 400 degrees internal which is probably ok but on the low end. See any smoke out the chimney? That’s probably the best way to determine if the cat is working or has stalled. Is this a Woodstock stove?
I agree; in flue temps are about twice the on surface temps.

But It depends on what thermometer is there and how the scale is added to the pointer; some indicate the estimated "in flue" temperature and the actual measured on surface temp.
e.g.
1666197091274.png

to the OP: What is the thermometer in this case? I see you have two scales on the thermometer. What is the one you read?
 
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Is the stove connected to a 6" stainless liner in the chimney or a clay tile liner? If clay tile, what size or ID?
 
I lived there until near 30 y/o.
My problem was that I had an magnetic old stove pipe thermometer that had two scales. One reflecting the temperature that it actually was experiencing, and one that multiplied that by a fudge factor of around 2 that was the estimated flue gas temp.

The problem here is the factor of "about 2" is close to the C->F factor (100 -> 212). Ultimately the problem was my brain was not working right due to something else having priority there. I guess my multitasking abilities keep going down with age...
 
@begreen had a 6" smooth wall stainless steel/titanium liner wrapped with 1" insulation put in just last year.
That should work pretty well. Is it a 1 or 2 story chimney?
 
@begreen It's a 2 story.

@Ashful it's funny, I find that for reloads the fire actually burns more actively as soon as the catalyst is engaged, as the secondary burn tube (it's a hybrid stove) really start taking off after I close the bypass. Hence why I was asking if it was ok to do it right away rather than waiting.
 
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Ok, so after some trial and error it seems that running the stove with the air completely open for at least ten minutes after engaging the cat and then gradually cutting the air after that works best. The most I'll see come out of the stove is some light wispy stuff which I assume is just steam.

If I cut the air at all sooner than that I get some light grey smoke that comes up about 3 feet out of the top of the chimney and tails out a short distance - is that to be expected or should I be concerned that my cat is not operating completely effectively? Because of the secondary burn tube if I am running the stove hot I won't see smoke anyway, cat or not. Should also note at no point does the cat temperature drop out of the active range, in fact it stays well on the hot side.
 
That sounds good to me. That’s pretty much how I operated all my cat stoves. After reloads I always ran hot for 5-15 minutes and watched the thermostats then turned air down in stages til I got where I want. Pretty much the same way I run a non cat too.
 
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Do remember that cat probe thermometers have a long time constant, maybe something close to 5-10 minutes. So, you say your cat never falls out of active when shutting down too quick, but the fact that you see smoke under this condition is indication that it may actually be doing just that, but that your thermometer is just too slow for you to confirm it.

But I like the way you dialed in your process, by plume, rather than by probe. I've been waiting for our weather to turn cold enough for daylight reloads, so I can check and see if my combustors are actually still working as well as I hope or believe, but all of my burning so far this fall has been in the dark evening hours.
 
Ok. I'm not sure you would notice the condensation by looking from the outside; if the pipe is installed correctly, it'd drip into the stove (if no elbows are present).

Is the thermometer reading correctly at room temperature? Do you have another way of checking the temperature to see that it is working well?

Cat stoves can indeed have low flue temps, but the general advice is to keep it above 250, especially this low in the flue; it'll cool down further up the flue. Water condensing is a good way to end up with creosote, as that water will capture smoke particles.

This is also why cat stoves do best with a double wall stove pipe; keep the already low gases from cooling down too much thru a single wall pipe.
So I have a question, if one uses a double wall interior black pipe which I am considering when my new Mansfield arrives . So question is how does one properly measure flue temp with double wall pipe ?
 
Yep, a flue probe thermometer. I have the one from Condar.
 
So it turns out my worry about the stovepipe temperature was misplaced; I replaced my thermometer with one specifically designed for stovepipes (Condar Chimguard) and it turns out it's typically staying above 300, which honestly makes more sense and matches better with what I've been seeing from the stovetop.

I've been running into issues with the cat getting very hot when trying to fully load for an overnight burn, but from I've been seeing elsewhere new cats tend to be very reactive for a month or so, so I've playing it safe and doing light loads at night until it slows down.
I've also noticed that closing the air a bit to bring it down to a medium/medium-high burn before engaging the cat helps slow down the cat temperature increase. As long as the secondary burn tube is going pretty good it still burns very cleanly before engaging.
 
The temp probe on the side of these Mansfield Cat stoves can be misleading. Things to consider:

The temp probe is heavily effected by the temperature of the stove itself over in that corner. Slow to rise on a cold stove, and slow to fall coming down from a hot stove.

On startup from cold, the temp probe is way off in the corner. Waiting for it to read "active" while bypassing it would take far longer than is likely necessary. I engage the cat when the temp probe on the stove pipe is up around 550-600F on that initial startup. The stove temp probe jumps up to "active" within a minute or so after engaging.

On reloads, it's common for that temp probe to still be in the bottom part of the "active" range even though EGTs are like 300F from a bed of coals that haven't put out any wood gases in hours. The cat is not active. Don't trust the probe! It's just confused because it's getting too much information about how hot the stove still is. Bypass and run with the air wide open until the firebox is full of flames and the EGT's are back up in that 550F+ range. Then engage.

The cat in this stove is most active towards the end of the off-gassing stage, just after the fire in the box drops out. You'll hear it start to go "tink tink tink" pretty aggressively at this stage. This is when the cat is most likely to over-heat. The counter-intuitive part of this adventure, is that, lower burn rates actually lead to the flame combustion in the firebox shutting down sooner, which results in a significant amount of wood gases for the CAT to process. Higher burn rates will finish off more of the wood gases before collapsing, resulting in less work for the cat to do afterwards.

Best of luck!
 
I’ve played around with the fluegard probe and single wall pipe in the past trying to get a more accurate reading. Finally I just purchased an Auber thermocouple probe. They are very quick to read and much more accurate.