Stack Temperature

I measure stack temperature with a magnetic thermometer on the stovepipe about three feet above the stove outlet, below the barometric damper. My Harman manual says if stack temp is 500 degrees the stove is being fired at its maximum. Do they mean 500 degrees as measured by my stick-on thermometer, or do they mean 500 degrees as measured by a probe (which would be about 250 on the stick-on)?

I would think Internal Pipe Temp, the magnetic ones on the pipe are not that accurate anyway on a round surface.

My stack temp measured with a PROBE inside the pipe just before the brick chimney is around 175-230 Deg. F normally with it burning quite well. The prove is about 6 feet from the stove (After the baro damper).

rberq wrote:I measure stack temperature with a magnetic thermometer on the stovepipe about three feet above the stove outlet, below the barometric damper. My Harman manual says if stack temp is 500 degrees the stove is being fired at its maximum. Do they mean 500 degrees as measured by my stick-on thermometer, or do they mean 500 degrees as measured by a probe (which would be about 250 on the stick-on)?

Yes, basically it is the maximum temp at the center of the pipe. As far as relating the 500* internal probe to a 250* stick on, it would depend on the stick on more rather than less. You could put 5 on the pipe and get 5 different readings. Plus the gas speed would vary the percentage of heat loss from the center. The only accurate way to measure the temp is with a probe. That is not to say you can't operate the stove with a stick on. The changes tell the story, you are just using lower numbers.

By the way, 500* stack temp is nothing for a coal appliance. If you push one real hard, watch the stove pipe. When the color of the steel approaches that of a vigourous coal fire, make up your mind what your going to do because it will be a puddle on the floor in a few seconds.

The user manual I have for the Harman Mark series says on page 2 a Harman magnetic temperature gauge to monitor stack and stove temperatures is recommended. However, they leave out where they would recommend placing it on the stack, i.e. how close to the exhaust port on the stove. I have one about 18" above the exhaust port that reads about 300*F less than one that is on the sidewall of the stove (located just below the baffle weld line). The stack gauge usually reads between 200* - 300* F, but has been as high as 400*F.

Yeah, titleist1, you would think Harman could be a little more precise. Magnetic thermometers show the "normal" range for a wood stove to be 230 - 460 degrees, and everything I have read says the flue gases are about twice the surface temp. So I have to believe Harman means to keep the stack SURFACE temp below 500 -- coal stoves can't be that much more delicate than wood stoves that they can handle only half the temperature!

It's great that you see temps so much higher on the stove side as on the stove pipe. That says to me that most of the valuable heat is being captured from the gases before they go up the chimney.

WNY, if you have a magnetic thermometer, I would be curious to know the temp reading below the barometric damper (closer to the stove) and above the baro damper. Or at the same locations for your probe, if you want to make another hole in the pipe. Presumably some room air is drawn into the baro damper and reduces the flue gas temp.

mines not a hand fired, but I can let you know, I have some other probes and the mag thermometer, I will advise if I have time tonight.....

we just go hammered with snow(8-12"+), so I may outside a while tonight....

I lose about 100* in the stack after the baro even when closed.

I don't get it. Why are everybody's stack temps so high burning coal?

I use a good quality Ashcroft 5" dial with a 4" probe threaded into the stack pipe. So I know I am sensing flue gas temps which are ALWAYS 140F to 160F. Even lower when I have the damper cranked in.

The only time I have high flue/stack temps is when I leave the ash pan door open longer than I should or if I burn wood (good grief). As I type this, my stove is producing 215F in the heat accumulator and 150F stack temps measured 18" above the outlet. And the fire is glowing as bright as Mattheus after he polishes up his latest project!

I have my stove producing 250-270F in the heat accumulator by 11p. Stack might be 160F. But I'll be tucked away in bed only to see it at 6a.

My boiler will run about 110-125* on its natural draft. When the blower comes on it can run up there, on a long pull it may go 500-550*.

Is this a critical measurement when using a brick chimney?

shortcut wrote:Is this a critical measurement when using a brick chimney?

No, bricks make great chimneys. What it tells you is how much of your heat is going up the chimney. Each install will have its own set of #s depending on the unit, the chimney, the fuel, etc. As you get used to running the appliance, it will let you know when its happy.

Hey Cap, I think the reason you have so much cooler temps in the flue is that your stove has a built in heat exchanger, pulling heat from the gasses before they get to the flue, and that you have a lot of surface area in your Harman SF250, pulling more heat out of the gasses.

Are you still using your firebox reducer??

Greg L

Greg,

yes, I am still reduced by 50%. With temps varying between 25F and 40F, I am able to maintain reasonably warm temps in the house and 120F --150F in my domestic hot water tank. This year, I installed a 12" x 24" vent directly above the stove and closed up some other vents. So all of the hot air goes directly to my living room. As a matter of fact, the opposite side of my basement, 28' from the stove doesn't exceed 65F while my living area is above 70F. I am burning about 50lbs a day. Last year, with my 20% reducer installed throughout the colder months, I burned about 80lbs a day.