flue temps and temps outside?

[Mikewelland]

Hello all.

First of all I would like to say how wonderful everyone is here, being a new stove owner myself sometimes I think I have stupid questions but turns out that everyone is very helpful. Thanks guys ( and girls )

I am just curious about flue gas temps, I have a Pacific Energy Super 27 stove with a double wall stack and a probe thermometer 18" up from the stove and I am hearing very many conflicting tales about temperature ranges.

On one hand I hear that Anyone who says that you should aim for a particular flue gas temperature or even a range in temperature is setting you up for failure because steady-state burning is almost impossible to achieve? is this true??

Also I thought that there is no correct operating temperature for wood stoves because their output is modulated to provide enough heat for the conditions. So, in cold winter weather the temperature will be higher than in the fall when the heating load is lower. (this seems to make sense to me, as I live in a place where one day it can be -1 and the next day it is -45, when it is -1 outside I dont want my house to be 30 just because I have to keep a certian flue gas temp??)

I also heard that your flue temp should be on the minimun of 300 or I have heard 250 I Have also heard that it should be a minum of 500???? what is correct???? does it all depend on what kind of stove I have, wood I am burning?? etc??

I also see that once the secondary burn kicks in on my stove my flue temp goes down?? is this normal??

any help would be great, seems like everywhere I look I get conflicting answers, would be good to get a straight one.

once again, I hope this is not a stupid question

 

[firefighterjake]

No such thing as a stupid question here . . . questions asked repeatedly every year (i.e. cat vs. non-cat stove, stainless steel vs. poly chimney brushes, steel vs. cast iron vs. soapstone stoves) and statements made repeatedly every year (i.e. my new EPA stove sucks) . . . but no such thing as a dumb question . . . and even the repeated questions often get politely written replies.

Generally I try to run the stove around 350-900 degrees F -- the safe zone of my Condar probe thermometer. I generally try to aim for around 400-700 degrees F. Of course, these are the temps with a probe style thermometer on double wall pipe. Surface mount temps on a single wall will be quite different.

Woodstove thermometers and temps -- These temps seem to vary a lot more than the temps on a flue . . . namely because it seems as though how hot is too hot varies a lot according to the various materials that go into a stove. As a general rule, it seems as though folks with steel stoves can run them a lot hotter than cast iron and soapstone . . . within limits of course.

How much do I rely on the flue thermometer? Quite a bit actually . . . I use the flue thermometer more often than I do any other thermometer (stove top or my IR) . . . it is the one temp that I look to when deciding when to start cutting back on the air to get a good, sustained secondary burn (although the stove top temp helps somewhat.)

Normally . . . secondaries start . . . flue temp may dip some.

 

[Mikewelland]

Thanks for the reply "firefighterjake" so as long as i dont let my flue temp drop below 350 I should be ok? I had my flue temp up to 440 last night, turned down the air intake a bit and got that secondary burn going, sat down for a while then when i checked the temp again it had dropped to about 300, quite a bit of a drop I would say.so I opened the air intake up a bit more to get it to climb back up, what is the optimal temp to reload the fire box? or does that matter?

 

[firefighterjake]

Well your flue temp will inevitably drop as you to through the burn cycle and progress to the late coaling stage . . . but it's OK as there isn't a lot of the bad stuff or moisture left at that point to gunk up your flue.

During the "main event" with the flames and early coaling stage I try to keep my flue around 450-650 degrees F (I know I said between 400-700 in my last post . . . but this time I actually looked at my thermometer on my flue ).

Sometimes you will get a drop in the flue temp when you get the secondaries going . . . honestly at this point perhaps the two biggest indications that things are going well is if a) you have sustained secondaries and b) you go outside and see little to no smoke coming from your chimney. Well, actually, we could also say c) your fire doesn't go out or look as though it's about to be snuffed out.

Sometimes it's the draft and you cannot cut back the air as much . . . sometimes it's the wood and you may find it is not as dry as you may have thought . . . and sometimes it's the stove is not up to optimal temp. Each stove and the set up is different so don't take this to gospel, but for me I find that at around 400-500 degrees F (stove top temp) I can start cutting back on the air control without it affecting the flue temp too much in an adverse fashion.

I reload the stove when I need the heat . . . when it's wicked cold like it was yesterday this may mean reloading a little sooner in the coaling stage. When it's not quite as cold I reload later in the coaling process. I rarely, if ever, use the temp of the stove or flue as the guide to when to reload . . . only when to start cutting back the air control.

 

[Osagebndr]

Very good advice there ffj. I usually see flue temps with my probe therm at 450-700* depending on how hard the stove is running. Trust me mike when you burn good dry hard wood your stove will go where it wants. Do you have a stove too thermometer? I will always check flue temps when starting the stove and depending on how the fire is burning from the start I'll go by the flue temps and the fire to start shutting down the air. And my flue temps don't always drop much during secondary burn until later in the burn cycle. Lots of variables to consider .
Dry wood is a must however and wet wood will as difficulty and frustration to the learning process.

 

[Mikewelland]

Awesome! Great advice guys. I do not have a stove top thermometer but it is now on my list of things to get within the next couple days.

Where is the best place to put the stove top thermometer?

I am getting a cord of birtch delievered this weekend so I will see how that goes. And I will post my results...

Thanks for all the awesome advice. You guys really helped alot.

 

[firefighterjake]

Placement of stove thermometer . . . not sure with the PE. Perhaps some PE owners will chime in. With my particular stove the manufacturer suggested one of the four corners on top of the stove. I experimented a bit to see which corner was the hottest and it ended up being the rear right corner. Since getting the slab of soapstone I've had the thermometer in a different spot which seems to be OK . . . although when I want to get a more accurate reading I'll take my IR thermometer and shoot the corner as I can still do so with the IR thermo.

 

[jetmech]

great reply firefighterjake, i rely on my flue temp as well to regulate my primary air, i have single wall pipe and try to keep it below 450.. once settled in my pipe will cruise around 300 then slowly drop. also i remember a great line on here from a while back about stove top temps and pipe temps compared to the tourtice and the hare... stove top eventually catches up with pipe and passes it... good stuff

 

[Mikewelland]

hello guys,

well I thought I would give you an update following my question. I have been keeping my flue temp anywhere from 400 - 600 degrees during burning, at cruising speed it usually hovers around the 500 degree mark before it starts dropping, so thanks to all your help so far,

 

[CI-Borg]

hello guys,

well I thought I would give you an update following my question. I have been keeping my flue temp anywhere from 400 - 600 degrees during burning, at cruising speed it usually hovers around the 500 degree mark before it starts dropping, so thanks to all your help so far,

I just have a little Jotul 350 Wintersport insert. I have a thermocouple just above the stove outlet inside a offset adapter and a digital readout full time. Normally, the insert runs 500 to 800 degrees F but if I put dry splits on a hot coal bed it will get over 1100 degrees. The secondaries at that point look like blow torches coming out the holes on the secondary tubes. Pretty spectacular and and a little scary. That only lasts a half hour or so before it starts to back off. It's interesting to watch.