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Jotul Firelight 12 thermometer location

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by Joful, Feb 1, 2013.

  1. Joful

    Joful Minister of Fire

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    So, with both stoves cruising at 500F, running 2.5 full loads per day, we're still barely keeping temps up to 68-70F, and often running some oil. I've also noticed how hard it is to hold these stoves below 500F with some types of wood (particularly Walnut, believe it or not!), without getting into catalyst over-temp situations, and it's hard to get the cat to light off (even with my better dry wood) without getting the stovetop up to at least 650F. It's got me thinking... I may be measuring the wrong temperature, and thus running these stoves way too cool!

    Here's what I know:

    1. The Firelight 12 specifies no location for any thermometer, or any range of safe or maximum operating temperature.

    2. The Firelight 12 has a cast iron top load door (single layer, webbed, maybe 5/16" thick), upon which I've been measuring my temperatures. It's the hot spot, and very responsive.

    3. Jotul does specify a thermometer location for the Firelight 600, which is the non-cat twin to my stove, this location being the rear corner of the stove top. These stoves share most of the same castings, but the F600 lacks the top-load door of the F12, thanks to the reburn system.

    4. When I see 600F on the top load door, I see only 400F at the rear corner, where I'd be running the thermometer on the F600.

    So, am I running my stove at "400F", or "600F"? More importantly, when I'm cruising all day at 400F on the top-load door, am I really running the stove at "250F", the temperature I would see on the F600-specified thermometer location?

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  2. topoftheriver

    topoftheriver Member

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    just use common sense. Every stove runs differently. I just looked at my manual and it didn't say anything about it, but in all of my research I have seen a picture with thermometers in each of the four corners. I would say it is overkill. I have two and they are never the same. So then I have to say it is an estimate. The thermometer only measures the temperature of the surface. The temperature inside is at least double.
  3. webby3650

    webby3650 Master of Fire

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    I'm not sure why your manual doesn't show you where to put the thermometer, the current manual for the Oslo does.

    The picture you see with a thermometer in each corner is the pic that's in the manual. It's showing that it can go in any of the corners, not that you should have 4 thermometers.
  4. topoftheriver

    topoftheriver Member

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    I stand corrected. Page 16, figure 12 indicates the location of the thermometer. I thought I had seen it some place else. I have the original manual but I also downloaded the PDF manual from Jotul as a spare in case I loose the original for some odd reason. You are correct.
  5. Joful

    Joful Minister of Fire

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    Actually, the temperature inside could be 100x, when you start a cold stove and the thermo on top reads 100F. Similarly, the trouble here is that the top load door is very responsive, whereas the rest of the stove is very slow to respond to the heat in the firebox. I'm honestly unsure how the Firelight 600 folks even drive that stove with the thermometer mounted in a location where the temperature takes almost forever to change at all. I suspect I could get my top plate to 900F pretty quick, and still have the corner location shown for the F600 reading 350F.

    That brings us back to the point... I could destroy the top door, when the rest of the stove is almost stone cold. Then again, does 700F on the top load door, when the main part of the stove is at 400F, really mean I'm close to doing any damage?
  6. dznam

    dznam Member

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    Wow, 500* stovetop on two Firelight Model 12s and only 68-70* in the house! You must have a large or drafty or modestly insulated house, or some combination thereof. We've run a Model 12 at one end of the house since '97 and we'll only run the stovetop that hot on the very coldest of days up here in Maine - it's a massive heater. We're typically running stovetop temperatures of 350-400* with the cat running in the roughly 500-1000* range. At 500* stovetop, that side of the house (2000 sq ft) is in the high 70s when it's 15* outside and you don't want to be sitting near the stove.

    Maybe it'd be helpful to share a few thoughts based on my experience with the stove (below). Of course, YMMV.

    The '97 manual for the 12 states that the cat should not be operated above 1800* . You're having trouble getting into cat over-fire territory with a stovetop temp of 500*? I have never seen anything close to those kinds of cat temps running the stovetop at 500*. Are you using a probe thermometer located in the access hole in the cat chamber or are you using an IR thermometer? If IR, I'd suggest you try a probe, perhaps you'd get a more accurate reading.

    My cat lights off with a stovetop temperature (measured in the center of the stovetop) of about 350*. This is when I can reliably close the damper, watch probe temps climb quickly and watch the smoke plume at the chimney top disappear. The manual states that, "Once the stove and gases have been warmed to the 500-700* F. range, any gasses reaching the catalyst will ignite", so (if you're running the the original Corning Cat or equivalent), I suppose your 650* light-off temp is about right. I don't have any explanation as to why my light off occurs at a lower temperature other than the fact that I'm on my third cat and it's not a Corning (Condar). Perhaps the newer cats have catalysts which become effective at lower temperature. Having said that, I recall cat light-off being around 350* with each of the two previous cats. Light off- did start to climb on those cats when they got dirty (almost never) and when they got near the end of their service life, though. 650* stovetop on this stove is extreme (to me) and I've never had cause to run the stove that hot.

    I wouldn't use the F600 instructions as it's a completely different design. It'd probably be more relevant to use the Isle Royal directions for location. In any case, I use the same location you do and my stove runs just as it should. Imagine what your cat temps would be if you used the F600 location to run your stove?!

    On a somewhat unrelated note, I once loaded the stove for the evening and went to bed. The wind picked up that night to a constant 40 mph. That kind of wind dramatically increases my chimney draft. I woke up to find out that the porcelain on both sides of the cat chamber had bubbles in it! According to wikipedia, porcelain has a melting point of 2550*! Ouch. I installed a damper after that and now pay more attention to the wind forecast! I also picked up a Tel-Tru - best little woodstove toy I've ever had.
  7. topoftheriver

    topoftheriver Member

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    I have never run into that problem. First of all my stove almost never goes out. It only goes out if I am away for a day. But even when I had to relight it, I haven't experienced any problems ever and once the stove is at operating temperature, it runs normally. Unless my thermometers are incorrect, my operating temperature is usually 350-550 degrees. Once in a great while, I will put a bunch of small wood in and run it up so that I can burn out the chimney pipe. But I can say I haven't had bad creosote problems. My stove is cooking away as I write. The temp on top is around 475 and it is warm in here. I have 2500 sq ft and it does a good job. All areas are as the should or at least the way I want it.
  8. Joful

    Joful Minister of Fire

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    Wow... great info! I'm so glad to see another Firelight 12 user out there, as there don't seem to be many of us here.

    The house is large, drafty, and the 1773 wing is entirely un-insulated stone [1]. However, I agree that two F12's should be able to heat better than I've been doing. There are reasons why that's not happening (wood supply, reload schedule, etc.), but I won't bore you with those details, here.

    I had been running the stove more like you, just getting the cat up to 500F, and often not much higher. I am running a Condar Steelcat. However, after complaining that my chimney was still smoking [2], and that my cat temp would often dip as I lowered my air control (rather than rise, as it should), other F12 owners convinced me I was running way too cool. Seems many others are shooting for 1000+ on the catalyst (yep, I have a probe in the access hole above the catalyst on each F12), and I've been doing the same more recently. If I can get the cat up above 750F on the initial closing of the bypass door, then I find I don't have any smoke out the chimney, and have no trouble with it falling out of ignition when I shut the stove down. Of course, my burn times are shorter, than when I was keeping the cat in the 500's.

    I think that if I were to engage my cat at stovetop = 350F, it would probably never get up to 500F on the cat probe. When I get the cat to shoot up above 750F on the initial engagement, I find I can (usually) get both stoves cruising beautifully for hours, with 450-500F on the stovetop, and 1500F on the catalyst. They seem to just sing in this mode, but then my less than perfect wood burns out in 7-8 hours, and I'm not around to reload for 9 - 12 hours.

    The trouble with the cat going over temp is related to two factors, I think: 1. Burning walnut. Seems that wood must be crazy high in resins, or something. It drives my catalyst temp thru the roof, the way Poplar, Sycamore, and Oak never will. 2. How early I engage the catalyst. If I burn longer in bypass before engaging, perhaps at a lower air control setting, then I can usually avoid any trouble with the catalyst wanting to go over 1800F. In fact, even if I engage early, if wait an hour before shutting the primary air down tight, then I can usually avoid cat overheating. All has to do with how quick the volatiles are coming off the wood in the first hour of the burn, I suppose.

    One of my F12's is a later model, and installed on 26 feet of chimney. The other is 1993 vintage (first model year?), and on a shorter chimney, perhaps 15 - 19 feet. The newer one on the tal chimney is a breeze to get going and into cat mode, whereas the older one on the short chimney seems to take forever to get where the cat will really light off. I can go from coals to set up and cruising in 20 minutes on the newer F12, but rarely less than 45 minutes with the older one on the shorter chimney.

    Thanks, again!

    [1] - Thermal imaging: http://www.hearth.com/talk/threads/old-house-thermal-imaging.104400/

    [2] - Smoke / running cat at 1000F+: http://www.hearth.com/talk/threads/white-sky-smoke-failing-cat.103391/
  9. Joful

    Joful Minister of Fire

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    One other thought, dznam... what are you burning? I just got started last year, so only my softwoods are well seasoned. The hardwoods burn, but they could use another year or two in the stacks. A large part of my difficulty with the cat is likely the fact that I need to do the last bit of seasoning in the stove, basically making sure the water is steamed out completely, before I can ever engage the cat.
  10. dznam

    dznam Member

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    I think you're on to something with your seasoning thoughts. I burn red and white oak, Ash, Sugar Maple, Red Maple and Spruce. I recall a winter about 5 years ago when my wood was not adequately seasoned. I had the same issue you have experienced with getting the cat to light off. Everything I'm burning now has been seasoned for 2-3 years and is in the mid-teens in M.C. Interestingly, even when burning the Spruce (extremely resinous, especially the "stump splits" which are near-cousins to fatwood), I do not have the issue you have experienced with the Walnut.

    My chimney's are each about 25' and have good drafts. I have run Model 12s at both ends in the past, and they've operated well at both locations. One other thought - I did run a 12 up at camp in a chimney that has a less than strong draft and I had the same type of light-off problem you're describing whereas my NC30 and the Elm worked well there. Based on these experiences, I think the 12 is very draft-sensitive and really needs a strong draft to operate well. Perhaps draft strength is a contributing factor to the performance of your '93?.
  11. dznam

    dznam Member

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    One more thought... I recall reading somewhere about an issue with the Steelcats (this was a while ago). If I'm remembering correctly, some owners experienced deteriorating performance (rising light-off temps) early in their lives. The issue appeared to be resolved by the owners switching back to ceramic cats. Maybe you could swap cats between the stoves to see if the issue is cat-related (even if they're both Steelcats)
  12. Joful

    Joful Minister of Fire

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    With a few weeks on both of these stoves, I'm now pretty well convinced the difference in chimney heights is my primary problem with the older stove. Identical loads always seem to be ready for cat engagement in about half the time in the new stove, on the taller chimney. I can run with this new stove shut down, 1500F on the cat probe and 450F on the stovetop, for hours and hours. No concerns with back-puffing, either.

    I have noticed the species I'm burning can make a big difference in how hot I have to get the stove prior to the cat taking off. Throwing three splits of my 1-year oak in on top of an equal amount of something dry (poplar, sycamore, or maple) seems to be the magic recipe, in that regard. A load entirely of poplar or softwoods seems to require a lot more time and temperature to achieve light-off (not enough good gas for the cat to chew?), and a load entirely of oak takes forever to get going, given the insufficient age of my wood stacks.

    I have considered swapping the cat's, and now that I have some time on both stoves and a good feeling for the characteristics of each, now may be the time. Trouble is... finding a moment when both stoves are shut down. I usually like to vacuum around the base of that back plate, and in the cat chamber itself, before reinstallation. Because of the down-draft design, it seems we get no fly ash clogging the cat, the way the Woodstock folks seem to report. Instead, I find all the fly ash sitting in the floor of the cat chamber, 6" below the cat.
  13. dznam

    dznam Member

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    I'm a "Woodstock guy", too and you're spot on. I need to clean the ash from my Progress' pre-cat screen regularly. I let it go too long last month and it was almost completely clogged. OTOH, my 12 has never accumulated any ash in the cat. I only inspect it once a year, after the burning season, and have never had any clogging. The Jotul cat is also easier to access/change. The Jotul 12 is the best stove I've ever burned for many reasons - hopefully this one will last long enough for Jotul to get back into the cat stove business! I remember your search for your 2nd 12 and recall thinking, "I understand exactly why he'd go to the ends of the earth to find this stove."

    I follow the same procedure that you do - smaller, easy lighting splits (spruce or red maple) on the coal bed followed by large oak/ash/sugar maple splits. Do this at bedtime, fill 'er to the gills, don't bother to give it time to get the fire going, just immediately throttle it down for the overnight burn and reliably wake up to a 350* stove.
  14. Joful

    Joful Minister of Fire

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    Hmm... maybe I should try throttling back sooner, myself. Can you detail your procedure, specifically, when do you engage the cat and when do you throttle back, when doing this?

    I did wake up to two stoves around 375F this morning, and they weren't even that full last night. Loads were 20% maple with 80% oak and dogwood, and of course, I spent 40 minutes getting both stoves loaded, heated up to 550F, cat engaged, and then throttled back in increments over 15 minutes.

    Glad to hear you like the F12, even after using a Woodstock. Another forum regular has told me the same, but only ever having used the F12, I really didn't know how worthy it is, compared to others.
  15. dznam

    dznam Member

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    I do engage the cat immediately. Generally, the stovetop is around 300* when I do this and it probably drops further with the new load in there. Have followed this procedure for years without any problems and it lets me get a good overnight load in there and head up to bed immediately instead of hanging around waiting to "toast" the wood with the cat bypassed. I do this regularly during the day, also.

    Interestingly, I do not get any coaling in this stove - it's the only stove I've ever had where coals don't accumulate - and I burn plenty of oak, etc. Same wood leaves coals in the Progress regularly. Wouldn't trade my 12 for the world!

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