flue temps and what they mean

[sixroses]

I just put in a internal flue thermometer and was surprised to see temps pushing 800 degrees. When I shoot the stack with my infrared I might see a high of 500. would a barometric damper keep a few hundred of those degrees in my boiler versus melting the snow off of the roof?? I am burning a GW 100 with great success but am always looking for better.
Steve

 

[Nofossil]

Internal stack temps are always higher than surface stack temps. The stack temp is affected by two things:

1) How hot the flue gas is coming out of the combustion zone
2) How effectively the heat exchanger removes heat from the flue gas

I don't know anything about the internals of your boiler, but typically you want the highest possible temperature coming out of the combustion zone - that's where peak efficiency is. There are a few things that can increase the amount of heat extracted by the heat exchanger portion of your boiler:

- Make sure the HX surfaces are clean.

- Reduce the flue gas velocity so that it spends more time in contact with the HX surfaces. Your damper might have this effect to some degree, but you don't want to smother the fire. The tradeoff is that you want enough air for complete combustion, but as little extra air as possible beyond that.

- Run cooler water through the HX - run the system at a lower water temp.

- Increase turbulence so that all the flue gas comes in contact with the HX surface

Don't know if any of these will help in your case. Maybe other GW 100 owners will chime in with their internal stack temps.

 

[sparke]

How long has it been since you cleaned your Hx? I would start there. When your Hx is clean you will see your flu temps lower and your boiler will perform much better. Your exhaust temp should be around 500* ... You may also have an over draft.