In one of the recent posts about flue size a person mentioned he thought the lower flue temps of the EPA stove was part of the problem with drafting on the new stoves, I was under the assumption you tried to keep the flue temp in the burn zone with or without a new type stove, I understand that overnight it will drop but when you are tending the fire during the day do you keep it in the burn zone on your stack temp. A lower stack temp will cause creasote problems no matter what kind of stove you have correct?
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laynes69
Minister of Fire
I don't think its a problem when the flue is properly sized and better yet insulated. When a flue is oversized it can create alot of problems. I have more draft now on a low fire with cooler flue temps than I did at almost full burn. All can be thanked for a insulated liner. Flue temps can be in the 400-500 range, and if the chimney is too big, those gasses can cool to under a 100 degrees at the top of the chimney. I know because it was my problem. An 32' chimney with a 7x11 liner.
Another question was some of the older posts on here stated that they did not worry about stack temps getting too high, but I always went by the guide lines on my stack thermometer so was not sure where they were coming from. My new rutland thermometer has 550 F as over fire and my older Condar has 450 F , what do you fine people consider over fire.
oldspark said:
Overfire to me refers to stove temp, not flue temp. If the stove metal is getting up to 900, it's in overfire range.
Flue temp depends on the stage of the burn, the stove and the flue system. When starting up the stove our flue may very well get up to 600, then settle down to about 400. With the old 602 I occasionally saw 900 °F flue temps. With the Castine 350-400 was pretty normal. As a counterpoint, some owners of downdraft (rear burners) report higher normal temps in the 800 range.
BLIMP said:
What size splits? Look at my avatar, that's 2 splits. 3 that size wouldn't fit. I think this also depends on the quality of insulation in the firebox. Some stoves do better with small hot fires than others.
This is how my question went the first time, humor me here, the stack thermometer has a "overtemp" range on it, are these number pointless?
Slow1
Minister of Fire
oldspark said:
I think it depends on your stove and installation (I just love that answer don't you?).
When I was burning my first stove (the downdraft) the ranges on the rutland thermometer seemed to match up rather well with what I found to work for me. Although a clean burn for me with that stove had to be on the high end of the 'good' range (entering into the low end of overfire). I seldom if ever would see it fall below the 'underfire' line.
Now with the FV it is a very different story. I have never been near that overfire line since installing the new stove. I regularly cruise below the "underfire" line and am not concerned about it. Folks at Woodstock don't give any "keep your flue temp above xxx*f" guidance so I don't worry about it.
My flue seems to stay clean enough as far as I can tell (I'll update on Thursday after I have my annual inspection done if different). The only thing that has built up on my cap with the FV is some ice in the colder part of winter (melts off when I reload or it warms up in the afternoon, whichever comes first).
Keep in mind that to get build-up of creosote in the chimney you need to not only be down in the condensation temperature range but you have to have enough VOCs, smoke particles, and water vapor to condense and create it. IF your stove is burning clean enough I would imagine that you simply won't have the right mix of ingredients in the flue to cause a problem. At least you won't have ENOUGH of the nasty mix to build up fast enough between cleanings to cause a problem eh?
Now draft - that is something I've wondered about since I believe draft is a function of temperature. I don't know the actual math calculations though so I can't even commend on how much the draft increases for a given increase in temperature. However I do wonder if this is one of those "as long as there is enough you are ok" sorts of things. Some stoves likely are more sensitive (have a more narrow range of 'good enough') than others so again it will depend on stove as well as actual flue and home design (as well as weather and...?).
I had a minor issue with draft I think. I was not happy last fall on starting up cold (reverse draft) and a couple back puffs that I thought were related to stalling draft so I added 3' to the top of my chimney and since then never had an issue. Ironically with the first stove I was convinced that I was overdrafting all the time and was ready to install a pipe damper for the new stove.
At any rate based on reports here it appears that most cat stoves do run much cooler up the flue than burn tube or downdraft stoves. Of course YMMV.
Thanks Pryo, I guess it is another varible, I burnt the old Nashua for 30+ years using my stack thermometer as a guide line, never any cresote to speak of and nice clean burns, so I assume I would burn the Summit the same way using the same guide lines but this may not be the case and will learn over the winter, (burnt stove 2 months this spring. I am not use to letting the stove stack temp getting in the over fire range after 30 years on avoiding it but it sounds like for a short period of time it will be no danger.
oldspark said:
The colored ranges are somewhat arbitrary guidelines. The actual temperature numbers are the reason for having the thermometer on the flue pipe.
The Summit will not burn the same as the old Nashua. Expect a learning curve as you get used to using the stove under a variety of conditions and with a variety of wood loads. With a full charge of wood, it is possible to get quite a temperature spike on the stovetop and in the flue, especially when the EBT kicks in.
Todd
Minister of Fire
The stove and chimney will be working as one system and there are many vairables with anyone system so temps will vary. I think the main thing to watch for me is for the flue temps to drop when I engage the cat. My external temps can go up over 500 easily while in the bypass mode and after I engage they drop in half in short order. Non cats will burn a little hotter flue temps but you should also see a drop when reducing the air down to a slow burn.
I know the summit will burn differently but I thought the temps for the flue stayed constant as far as the saftey guide lines, over fire is over fire no matter how you get it there. The new thermometers have basicaly the same temps on them as 30 years ago, still haveing a problem with getting the flue temp way up in the over fire range. I know the chimneys will take a much hotter temp but what the hell do the number mean on the thermometer, just that at the higher temp if can ignite any creosote that you may have? I may bea little anal here the guide lines are on there for a reason I assume.
laynes69
Minister of Fire
Here is a link that has some information on chimneys.
http://www.engineeringtoolbox.com/chimney-sizing-d_175.html
With flue temps and draft, I have seen .02" which is too low for the furnace when there was a low fire. Maybe 250-300 out of the unit. When those temperatures went to over 600, the draft would exceed .08" which is overdraft for the unit. I have a baro to control my draft, but most of the time it would be closed and draft would be too low due to the size of chimney. I recently lit a fire when it was about 50 out. Without secondary combustion, with a low fire my draft was .05" If that liner wasn't there to keep the temperatures in the flue up, I would have seen .01"-.02" with smoke spillage on startup. Where I had .02"-.03" before during last winter when the damper would close, performance suffered. Since my unit requires .04"-.06" all the time, I will see that this winter with the liner, and the baro will help keep the draft from exceeding my set point. So personally I have seen and measured huge draft variations during a single burn. I had low stack temps to the point of condensation and I had very little creosote in the chimney.
http://www.engineeringtoolbox.com/chimney-sizing-d_175.html
With flue temps and draft, I have seen .02" which is too low for the furnace when there was a low fire. Maybe 250-300 out of the unit. When those temperatures went to over 600, the draft would exceed .08" which is overdraft for the unit. I have a baro to control my draft, but most of the time it would be closed and draft would be too low due to the size of chimney. I recently lit a fire when it was about 50 out. Without secondary combustion, with a low fire my draft was .05" If that liner wasn't there to keep the temperatures in the flue up, I would have seen .01"-.02" with smoke spillage on startup. Where I had .02"-.03" before during last winter when the damper would close, performance suffered. Since my unit requires .04"-.06" all the time, I will see that this winter with the liner, and the baro will help keep the draft from exceeding my set point. So personally I have seen and measured huge draft variations during a single burn. I had low stack temps to the point of condensation and I had very little creosote in the chimney.
It might help to clarify that I was running the summit to keep the stack temp at 450 max with a little over shoot up to 5-6 hundred (makes me nervous) and I would reduce the air to get it back to 450, is this not the way to do it. I should have put the question this way in the first place. :red:
Todd
Minister of Fire
The numbers are a useful guideline imo. I think most liners are rated for a max of 1000 degrees at continuous use? So if your burning up in that range you may want to do something to get that down like a damper. At the low end I think somewhere around 200-250 is too cool and chances are high you could be burning a smouldering creosote factory but that can depend on the stove. Look at your fire and chimney as well.
Theres a number I have not seem before, 1000 degrees of continuous use, that helps, I wonder if the clay liner is about the same.
firefighterjake
Minister of Fire
oldspark said:
It seems as though once the flue is up to temp, even folks with marginal drafting chimneys do OK . . . most of the problems seem to be on the cold starts rather than reloads.
I can only speak for myself and what has worked for me . . . but I do use my probe thermometer as a guide as to safe burning -- not too hot, not too cold . . . but I also realize the numbers may be off and try to have a 150-200 degree buffer in case the thermometer is reading a little too high or a little too low. As for keeping the temp in the zone . . . as you no doubt know the temp will drop off on long burns as the fire progresses through the various stages . . . but at the tail end there isn't much bad stuff left for the temp to be a real issue . . . normally my temps in the flue are pretty constant and once I've got the stove up and cruising I don't worry too much about the temp since it doesn't really change much in the 4-5 hours before I reload it.
Once the wood gases are burned off and only charcoal is burning, lower flue gas temps will not create creosote. The exception being with damp wood which can take a longer time to outgas. With the new stove, if you don't see smoke coming out of the flue, odds are it is not going to have a creosote problem.
That said, there is a difference between a lazy draft and low flue temps. The concern in the other post is that even once the flue is fully warmed up, that the draft will be low. That can lead to smoke spillage on startup and a stove that doesn't start well even with the air control wide open. Think of it this way, which is easier to suck up water out of a glass with a straw or a 2" pipe?
That said, there is a difference between a lazy draft and low flue temps. The concern in the other post is that even once the flue is fully warmed up, that the draft will be low. That can lead to smoke spillage on startup and a stove that doesn't start well even with the air control wide open. Think of it this way, which is easier to suck up water out of a glass with a straw or a 2" pipe?
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