Hi we just got a new Heatherstone Mansfield with the new EPA approved catalyst and are wondering if we need to be concerned about lower flue temps than we used to run with our old Mansfield. When the catalyst is in the safe zone for operation and engaged, we often are not able to get flue temps above 250 . That's with a new double-walled stove pipe and thermometer at a foot above the stove. We're burning 100% elm coz that's what drops all over our farm. What we're burning right now is not as cured as we'd like yet -- long dead, but not split until fall -- so not ideal, but far from green. Should we be concerned about the lower flue temps, or is that fine as long as we watch the indicator for the catalyst and only engage it when it is in the safe zone?
Hearthstone Mansfield 2022 truhybrid low flue temp
- Thread starter wiscoburning
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Todd
Minister of Fire
What kind of thermometer are you using? Double wall pipe requires an internal probe type thermometer. A magnetic surface type thermometer will give a much lower temp on double wall compared to single wall pipe.
I'm using a magnetic surface one that the dealer gave me with the stove. It's the same one that I used with my previous Heatherstone Mansfield, purchased in 2000! And same double walled pipe. The old stove would easily run in what I was told was the ideal range, i.e. around 275-475. But maybe I was wrong all those years??
That will not work on double-wall stove pipe. You need a probe thermometer places about 20" above the stove for an accurate reading. The good news is that your actual flue temps are much higher, so no worry there.
mdocod
Burning Hunk
Starting from cold and measuring with a FlueGard internal probe about 18" above the stove I use the following startup procedure and it seems to be serving me pretty well:
Start Fire with CAT bypassed and air control wide open.
Burn with door open until roaring/rumbling.
Close the door at about 350-400F EGT.
Close the bypass (engage CAT) at 600F EGT.
Set air control to 1/4-3/8" open at 800F. (1/4" for larger fuel loads, 3/8" for smaller fuel loads)
Keep in mind, that I have 13' of single wall above the stove then about an 8' insulated chimney section, so there's more cooling/condensing in my system than on a system that is double/wall +insulated the whole way up, so this startup process may be overkill on target EGT's for your configuration, however, I would venture to bet that your wet elm is going to have a similar effect on the system as my large section of single wall, so you might be well served to target the same with that wood! I like starting out at this higher EGT as it ensures the chimney system is very well heated at the front end of the burn to minimize risk of condensed gases on the chimney/pipe. The Mansfield manual states that the stove will produce exhaust gases in the 500-1200F range and that this is normal. I figure, anything under 1000F at the meter 18" above the stove is probably fine, so targeting 800F leaves me a little room for accidental overshoot.
You'll find that in the time it took to run the stove up from 600F to 800F under that initial roaring combustion with the air control wide open, the little probe on the side of the stove will have jumped up to the "active" range. As long as you have a firebox full of roaring flames and EGT's above the stove measuring around 600F or better, I see no reason not to start sending it through the CATs. The probe on the side of the stove is not really in the direct path of exhaust while the cats are bypassed, so waiting for it to say "active" before engaging the cats is kinda backwards in my opinion. I have not had any issues engaging the cat in this manner and it sets everything in motion nice and quickly.
After setting the air control down to the desired rate for the remainder of the burn cycle, EGT's will steadily work their way down through the burn cycle from the initial 800F down to around 400F later in the coaling stages long after the flames in the box have gone out.
When the active flames in the box go out, you may hear the CAT "tink tink tink" during this part of the burn and the little gauge on the stove actually go jump up a fair bit during this part of the burn cycle. The remaining wood gases in the wood aren't enough to sustain fire in the box, but this is where the cats pick up the slack that secondary combustion can't do on its own. It's pretty awesome to observe!
That brings up an interesting point about this stove... If you ever hear it clink clink tink tinking, and see no flames in the box, but the temp probe on the side of the thing is getting up near or into the "too hot" zone, this means you have a whole bunch of combustion taking place in the cat. Your instinct at this point to correct the problem might be to close down the air control more. Doing this may actually make the problem worse. Opening up the air control to excite the fuel in the box to catch flame again will actually move that combustion back to the firebox/secondaries, and rapidly cool off the cat as a result. This also moves the heat output of the combustion back down lower in the box where it will have more opportunity to be transferred to the house. Alternatively, you can bypass the cat in this circumstance, but this will just send unburnt fuel up the stack, a waste of energy.
Over time, you'll learn what sort of fuel loads work best with what sort of air-control settings to burn through the fuel completely without getting into trouble at some mid-stage of the burn. I've found that in my setup, that 1/4-3/8" air control position that the stove manual suggests is a very reliable place to operate the stove when it has large to medium fuel loads. Smaller loads can get weird so be careful with that. Fully-closed should only be used to help draw down an over-excited active fire, leaving it in the fully-closed position through a burn cycle is likely to cause back-puffing and a premature transfer of combustion to the cats.
Good luck!
-Eric
Start Fire with CAT bypassed and air control wide open.
Burn with door open until roaring/rumbling.
Close the door at about 350-400F EGT.
Close the bypass (engage CAT) at 600F EGT.
Set air control to 1/4-3/8" open at 800F. (1/4" for larger fuel loads, 3/8" for smaller fuel loads)
Keep in mind, that I have 13' of single wall above the stove then about an 8' insulated chimney section, so there's more cooling/condensing in my system than on a system that is double/wall +insulated the whole way up, so this startup process may be overkill on target EGT's for your configuration, however, I would venture to bet that your wet elm is going to have a similar effect on the system as my large section of single wall, so you might be well served to target the same with that wood! I like starting out at this higher EGT as it ensures the chimney system is very well heated at the front end of the burn to minimize risk of condensed gases on the chimney/pipe. The Mansfield manual states that the stove will produce exhaust gases in the 500-1200F range and that this is normal. I figure, anything under 1000F at the meter 18" above the stove is probably fine, so targeting 800F leaves me a little room for accidental overshoot.
You'll find that in the time it took to run the stove up from 600F to 800F under that initial roaring combustion with the air control wide open, the little probe on the side of the stove will have jumped up to the "active" range. As long as you have a firebox full of roaring flames and EGT's above the stove measuring around 600F or better, I see no reason not to start sending it through the CATs. The probe on the side of the stove is not really in the direct path of exhaust while the cats are bypassed, so waiting for it to say "active" before engaging the cats is kinda backwards in my opinion. I have not had any issues engaging the cat in this manner and it sets everything in motion nice and quickly.
After setting the air control down to the desired rate for the remainder of the burn cycle, EGT's will steadily work their way down through the burn cycle from the initial 800F down to around 400F later in the coaling stages long after the flames in the box have gone out.
When the active flames in the box go out, you may hear the CAT "tink tink tink" during this part of the burn and the little gauge on the stove actually go jump up a fair bit during this part of the burn cycle. The remaining wood gases in the wood aren't enough to sustain fire in the box, but this is where the cats pick up the slack that secondary combustion can't do on its own. It's pretty awesome to observe!
That brings up an interesting point about this stove... If you ever hear it clink clink tink tinking, and see no flames in the box, but the temp probe on the side of the thing is getting up near or into the "too hot" zone, this means you have a whole bunch of combustion taking place in the cat. Your instinct at this point to correct the problem might be to close down the air control more. Doing this may actually make the problem worse. Opening up the air control to excite the fuel in the box to catch flame again will actually move that combustion back to the firebox/secondaries, and rapidly cool off the cat as a result. This also moves the heat output of the combustion back down lower in the box where it will have more opportunity to be transferred to the house. Alternatively, you can bypass the cat in this circumstance, but this will just send unburnt fuel up the stack, a waste of energy.
Over time, you'll learn what sort of fuel loads work best with what sort of air-control settings to burn through the fuel completely without getting into trouble at some mid-stage of the burn. I've found that in my setup, that 1/4-3/8" air control position that the stove manual suggests is a very reliable place to operate the stove when it has large to medium fuel loads. Smaller loads can get weird so be careful with that. Fully-closed should only be used to help draw down an over-excited active fire, leaving it in the fully-closed position through a burn cycle is likely to cause back-puffing and a premature transfer of combustion to the cats.
Good luck!
-Eric
Todd
Minister of Fire
That’s a pretty long run of single wall pipe! I could be wrong but isn’t the max run 10’ or less per code?
mdocod
Burning Hunk
There is no limit specified in code here. I think that's a Canadian build code.
That 10' maximum length pipe would have to be something that could work on a large variety of stoves, even stoves much smaller than the Mansfield. How does a 1.2 cubic foot stove work on a 10' run of single wall "per code" if this stove that's going to drive significantly more exhaust gases through it (thus maintaining a more even temp through the chimney system), can't do 13' ?
I can point to numerous modern stove manuals for very tiny wood stoves, that call out single wall stove pipe as a recommended pipe option where clearances permit, up to the maximum length permitted by build code.
This stove likes to run high EGT's, especially on the wood we burn here, and I prefer to set things off to a hot start so that a rein-rich chunk of wood will burn through cleanly rather than soot up the cats. This is a good setup to be able to drive high EGT's for a thorough clean burn, while still getting some of that energy back into the house.
That is correct about the single walled pipe in parts of Canada. We had single wall run about 20’ inside up to a cathedral ceiling where it then joined a stainless double insulated which was what was visible on the outside. Great draft and the single wall pipe helped to heat the loft and upstairs bedroom.
I am wondering how accurate the Fluegard probe thermometer is when used on single-wall stove pipe. This question has come up a couple of times recently. Have you asked them about this? If not, I will try to make some time to do this.
Edit: Just sent them an email.
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Todd
Minister of Fire
mdocod
Burning Hunk
Why are you "starting to wonder" all of the sudden?
Seriously you guys need to let it go on the single wall until you can explain how a 1 cubic foot stove can safely use 10' of it but a 3 cubic foot can't use 13' of it. You're clipboard warrioring. Watch some Mike Row to get some perspective.
Nothing sudden about it. this question has come up a few times in the past month. For perspective, I contacted Condar. They got back to me this morning. Here is their response:
Our FlueGard is designed and calibrated to read temperatures in a double wall stovepipe. We do not recommend using it in a single wall stovepipe as you will not get accurate temperature readings. If you were to use it in a single wall stovepipe I can’t tell you how much the temperature readings would be off as we have never tested it in a single wall stovepipe. For single wall stovepipe I recommend using our ChimGard surface thermometer. Although it isn’t going to give you inner flue gas temp it will give you the most accurate readings.
Apparently, the high EGTs are not being measured accurately.
Our FlueGard is designed and calibrated to read temperatures in a double wall stovepipe. We do not recommend using it in a single wall stovepipe as you will not get accurate temperature readings. If you were to use it in a single wall stovepipe I can’t tell you how much the temperature readings would be off as we have never tested it in a single wall stovepipe. For single wall stovepipe I recommend using our ChimGard surface thermometer. Although it isn’t going to give you inner flue gas temp it will give you the most accurate readings.
Apparently, the high EGTs are not being measured accurately.
mdocod
Burning Hunk
The Amazon listing I bought the Fluegard from talks about these being the way to get an accurate reading on double wall, but makes no mention of them being incompatible with single wall.
That said... the fluegard manufacture website:
Sure enough... Sorry I "assumed" that this was just part of the witch hunt over my single wall stove pipe (I mean, lets be honest, it probably is part of that witch hunt, but it's a valid part of it). We're at a point now where people on the forum are implying that I'm doing something illegal by using my stove in the manner that I am, so if I seem a bit trigger happy on the issue I am. The clipboard warrior badge is proudly worn here. That's a GOOD thing to a point, it's just not fun to be the one looking at the back of the clipboard trying to explain to the officer that the traffic light was broken.
Seems like it would be easy enough to figure out what the effect of double and single wall would be on this probe:
I made a test jig out of some thin sheet metal to create a little "double wall" simulation behind the Fluegard to see what the difference was.... The test fixture "standoff" surface temps are around 100F lower than the single wall stove pipe behind it, which is comparable to the differences I seem to recall between single and double wall in similar burn states.
I experimented back and forth and back and forth at various temps and jotted a lot of numbers down and took a lot of averages. Yep, there's a difference.
In the end I would say it reads about 7% higher on single wall than on double wall in the range I tested it at (~500-800F).
