Combustion gas analyzer reading off Greenwood boiler

[jpowell1979]

With the temperature tonight at a crisp -16 my Greenwood was really burning nice and hot and I couldn't resist taking a reading with my gas analyzer that I use when working on oil boilers. Here are the readings, tell me what you think.

stack temp 560F
O2 11.5%
CO2 7%
CO 610PPM
draft -.07 W.C.
efficiency 74.5%

I found out that the magnetic temp gauge on my stack is off by about 150 degrees cooler compared to the gases in the pipe.

 

[sgschwend]

From memory: I would think your draft is towards the top of the desired setting. I know the owner's manual show .05-.07 for draft. The 560F stack temp makes me feel like you could choke it down to the .05 number and recover more heat.

I hope you will try this, it would be great to see those numbers too!!

 

[ihookem]

Choke it down is great, but wouldn't it put out less heat. Since it is -16.

 

[pybyr]

Choke it down is great, but wouldn't it put out less heat. Since it is -16.

Decreasing the draft should slow the rate at which the combustion products pass through the heat exchanger -- giving the exchanger more opportunity to recover heat before it goes up the flue.

 

[Deere10]

I have a GW 100,love it so far. Where can i measure draft on the chimney. I have insulated ss 8 inch pipe I am not to keen on drilling into that stuff just for a draft measurment. I am only running 2 four foot sections but this is enuff to get me at or just over the peak of the shed. Stove is set 8 inches off grd on concrete pad and with the t at the rear of stove the total height of chimney is just under 12 ft w the weather cap. Thanks

 

[TCaldwell]

what brand and and model of combustion analyser are your readings from, does it offer the calculation, based on wood parameters, my testo 327 with your readings calculate a much lower effiency% the calculation testo uses is flue gas temp minus supplied combustion air temp, divide that number by the co2 value, then subtract that number from 100. with your, 560 deg- 70deg=490/7%co2=70, 100-70=30% combustion effiency. the high o2 reading and high stack temp might indicate too much draft, if draft was less, the o2 might be lower 6/8% range and stack temp would be lower increasing effiency. high burn garn numbers 251deg-55deg=196/13%co2=15.08, 100-15.08=84.92% combustion effiency

 

[jpowell1979]

The only way to reduce the draft will be to add a barometric dampner. I was also going to try cleaning the heat exchanger tubes and see if it lowers the stack temperatures much. I have not cleaned the back tubes since last spring and they could certainly use it.

I drilled a hole about 20" up from the tee and about 24" below my draft inducer fan. I have the draft fan wired to a timer so I can turn it on for 20 minutes or so to get it burning hot again after adding more wood.

 

[pybyr]

I have a GW 100,love it so far. Where can i measure draft on the chimney. I have insulated ss 8 inch pipe I am not to keen on drilling into that stuff just for a draft measurment. I am only running 2 four foot sections but this is enuff to get me at or just over the peak of the shed. Stove is set 8 inches off grd on concrete pad and with the t at the rear of stove the total height of chimney is just under 12 ft w the weather cap. Thanks

Do you have even a short bit of non-insulated going from the boiler to your insulated flue? If so, make a small port there (draft should, as I understand it, be uniform within the flue, except at/ near the top). I'd tend to think, though, that it's very unlikely that only 8 feet of 8 inch pipe would be at risk of creating too much draft.

 

[sgschwend]

You could slow the draft inducer fan down. Most have a speed control, if not use a motor type of dimmer switch.

 

[TCaldwell]

try the o2/co2 temp readings without the inducer after the hx tubes have been cleaned about 45 minutes into burn, apply the math and let us know the results, i am hoping we will be happily suprised

 

[2.beans]

The only way to reduce the draft will be to add a barometric dampner. I was also going to try cleaning the heat exchanger tubes and see if it lowers the stack temperatures much. I have not cleaned the back tubes since last spring and they could certainly use it.

I drilled a hole about 20" up from the tee and about 24" below my draft inducer fan. I have the draft fan wired to a timer so I can turn it on for 20 minutes or so to get it burning hot again after adding more wood.

if you can remove a section of chimney pipe that will also lower draft, also you can install a flap like the old wood stoves inside the pipe up close to the boiler.