flue thermometer before or after pipe damper?

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sksmass

Member
Dec 21, 2009
203
Western MA
So, I think I want to install a flue damper in my setup and also a probe flue thermometer. I have a one-year old Woodstock Fireview. It exhausts through a 6" liner in an inside masonary chimney that is ~30' tall. I feel like my flue temps are too high -- like I am sending a lot of heat up the chimney. I gather, from reading Hearth.com, that a pipe damper might increase my efficiency. While I have got the drill out I figure I'll tap the pipe for a probe flue thermometer too.

But, I have three questions before I go taking anything apart and drilling holes in it:

1) can I install the damper in the middle of the 24" horizontal pipe run (in pic below)?
2) should the hole for the probe flue thermometer be before or after the damper?
3) should the probe thermometer be set vertically or horizontally?
 

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Unless you have an excessive overdraft with this setup, a pipe damper won't help you a bit.

How much chimney is above what we see? How long can you go between reloads? What sort of stove top temps are you seeing?

pen
 
Readings on the top surface of a horiz. pipe are bound to be high. Put the thermometer above the tee for awhile and see if they make you more comfortable.
 
pen said:
Unless you have an excessive overdraft with this setup, a pipe damper won't help you a bit.

How much chimney is above what we see? How long can you go between reloads? What sort of stove top temps are you seeing?

pen

I'm not sure if I've got excessive overdraft. It is a 30'+ above the T, through an interior chimney. Is there a way to measure draft? If I open the top of the stove and use the "match test" to check draft, the breeze will blow the match out.

Lately my pipe temps are almost as high as my stove temps at 500-600. If I reload around 10pm I have only a few glowing coals under the ash at 7am and stovetop temp of ~200. So, practical burn times of <9 hours I'd say.
 
30' inside chimney...ill assume lined the whole way. You could benifit from using a key dampner, but like pen said you may only ever use it sparingly due to outside conditions.

If you have to place probe on the horizontal run, mount horizontal too.
 
Sounds like a pipe damper would be worth trying then. Also agree w/ BG's suggestion on the probe.

pen
 
So your magno thermo is reading 500 - 600 ??? If so then your gasses are 1000-1200. A bit high there. As far as a flue damper, I have one, but I have an up, then 90, then out setup and the damper is first thing on the collar. 18 inches above that is the probe.
 
shawneyboy said:
So your magno thermo is reading 500 - 600 ??? If so then your gasses are 1000-1200. A bit high there.

Really? I always figured the difference between pipe surface temp and actual flue gas temp was less than 2X.
 
sksmass said:
shawneyboy said:
So your magno thermo is reading 500 - 600 ??? If so then your gasses are 1000-1200. A bit high there.

Really? I always figured the difference between pipe surface temp and actual flue gas temp was less than 2X.

Perhaps I am wrong but I thought the rule of thumb waw 2x on single wall. I have double wall with a probe so I dont use a magno thermo.

Shawn
 
Is that single wall pipe? Probe thermometers aren't accurate for single wall and not recommended. Looks like your thermometer in your picture is right next to the stove, this will give you a higher reading. It should be at least 12" up from the stove exhaust collar. Check and see if there is a difference in readings further away and also a difference between the top of the pipe and side. 30' chimney is pretty tall, a pipe damper may be a good idea but I know this stove has a lot of control. What air setting did you have set at for that 9 hour burn? Can you still get flame at 0? Maybe you just need to dial it down a little more? If I was to put a pipe damper on I would put it as close to the exhaust collar as possible and monitor the temps a foot or two above it.
 
shawneyboy said:
Perhaps I am wrong but I thought the rule of thumb waw 2x on single wall. I have double wall with a probe so I dont use a magno thermo.

Shawn

From a bunch of us playing around w/ these things last year, that rule is more of a guess. If you choose to use the probe, my suggestion is to not read it as though it is gospel. Take the readings w/ a grain of salt and consider what is going on w/ your stove, the look of the fire, etc to determine what your actual redline is.

pen
 
Todd said:
Is that single wall pipe? What air setting did you have set at for that 9 hour burn? Can you still get flame at 0? Maybe you just need to dial it down a little more? If I was to put a pipe damper on I would put it as close to the exhaust collar as possible and monitor the temps a foot or two above it.

Yes, single wall pipe. I usually run at about a setting of 0.75 for a long burn. I can't close it to zero without it starting to look starved.

So, if I can summarize the feedback here, it sounds like there may be no benefit, but also no harm in my installing a key damper in the 24" horizontal run, as close to the exhaust collar as possible, and to continue using a surface thermometer on my single wall pipe, but to take the readings off the SIDE of the pipe about a foot or two downstream of the damper.
 
sksmass said:
Todd said:
Is that single wall pipe? What air setting did you have set at for that 9 hour burn? Can you still get flame at 0? Maybe you just need to dial it down a little more? If I was to put a pipe damper on I would put it as close to the exhaust collar as possible and monitor the temps a foot or two above it.

Yes, single wall pipe. I usually run at about a setting of 0.75 for a long burn. I can't close it to zero without it starting to look starved.

So, if I can summarize the feedback here, it sounds like there may be no benefit, but also no harm in my installing a key damper in the 24" horizontal run, as close to the exhaust collar as possible, and to continue using a surface thermometer on my single wall pipe, but to take the readings off the SIDE of the pipe about a foot or two downstream of the damper.

I think maybe you should try burning at .5 and see what happens. Sounds like you still have some wiggle room on your air control. Also move that thermometer around and see what you get. I know I get much higher temps like yours close to the collar.
 
shawneyboy said:
Perhaps I am wrong but I thought the rule of thumb waw 2x on single wall. I have double wall with a probe so I dont use a magno thermo.

Last year I put a K-type thermocouple probe through one of the screw holes in my single-wall pipe. I connected the thermocouple to the receptacle on my IR gun and use the same instrument to measure both temps simultaneously. At a 600º external surface temp, the thermocouple hit 1200º before I pulled it out to spare the probe (max temp for my probe is 1200º). So, in my case, the flue gas temp was at least twice as high as the surface temp. That was for 8" pipe.

BTW the probe was glowing bright cherry red when I pulled it out, so I have to assume it was reading correctly.
 
Battenkiller said:
shawneyboy said:
Perhaps I am wrong but I thought the rule of thumb waw 2x on single wall. I have double wall with a probe so I dont use a magno thermo.

Last year I put a K-type thermocouple probe through one of the screw holes in my single-wall pipe. I connected the thermocouple to the receptacle on my IR gun and use the same instrument to measure both temps simultaneously. At a 600º external surface temp, the thermocouple hit 1200º before I pulled it out to spare the probe (max temp for my probe is 1200º). So, in my case, the flue gas temp was at least twice as high as the surface temp. That was for 8" pipe.

BTW the probe was glowing bright cherry red when I pulled it out, so I have to assume it was reading correctly.

As you said, that's w/ a K type thermocouple. Don't expect that from an analog probe in single wall as the OP is talking about.

pen
 
pen said:
Battenkiller said:
shawneyboy said:
Perhaps I am wrong but I thought the rule of thumb waw 2x on single wall. I have double wall with a probe so I dont use a magno thermo.

Last year I put a K-type thermocouple probe through one of the screw holes in my single-wall pipe. I connected the thermocouple to the receptacle on my IR gun and use the same instrument to measure both temps simultaneously. At a 600º external surface temp, the thermocouple hit 1200º before I pulled it out to spare the probe (max temp for my probe is 1200º). So, in my case, the flue gas temp was at least twice as high as the surface temp. That was for 8" pipe.

BTW the probe was glowing bright cherry red when I pulled it out, so I have to assume it was reading correctly.

As you said, that's w/ a K type thermocouple. Don't expect that from an analog probe in single wall as the OP is talking about.

I don't know nuttin' 'bout no analog probes. I was just agreeing with what Shawn said. The only thing that matters to me is how high the flues gas temps really are. Seems they are twice as high as the surface temp on single wall. Of course, if you have buildup low down in the pipe it will act as an insulator, so there will be an even greater disparity between the two numbers. Again, the only number that matters - the only one that you can base any computations on - is the actual flue gas temp. ;-)
 
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Battenkiller said:
I don't know nuttin' 'bout no analog probes. I was just agreeing with what Shawn said. The only thing that matters to me is how high the flues gas temps really are. Seems they are twice as high as the surface temp on single wall. Of course, if you have buildup low down in the pipe it will act as an insulator, so there will be an even greater disparity between the two numbers. Again, the only number that matters - the only one that you can base any computations on - is the actual flue gas temp. ;-)

No kiddin. However, the vast majority of folks on here measuring flue gasses aren't doing as you are (in particular the OP). The measuring device they have does not read accurately, but it does read consistently. Temps from a probe thermometer like condar's must be interpreted when used on single wall, not simply read and trusted. That is what I was trying to explain to the OP.

pen
 
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