can someone explain the correlation between flue gas temp and combustion efficiency

I can understand the correlation of percentage of oxygen in flue gas to ccombustion efficiency, but how does flue gas temp determine combustion efficiency, as proposed in www.donegalorganic.ie , leaflet on wood gasification. A little poking around with a thermocouple controlling a modulator for a variable speed fan seems far less expensive than a fixed mount combustion analyzer and a modulating fan , will they both accomplish the same end result?

Combustion efficiency calculations are based on O2/CO2 content as well as flue gas temp. Simply put , you want your CO2 as high as you can get it without starving the fire of air and the lower your flue gas temp, the more heat you are transferring into your fluid. The best modern gas fired condensing boilers will typically have flue gas temps only 15-20* above the RETURN water temperature.

heaterman, thanks for the explanation,I have seen your performanance stats on the garn, do feel as a installer there is any room for improvement, ie, draft modulation or increase during puffing based upon oxygen sensing or stack temp .

Not really TC......at least not cost effective improvements. You have to let some heat out the stack especially with a large water content like the Garn. If you lower your flue temps to much you'll get into condensation problems which can wreck a boiler in a hurry.

The Garn just works so well the way it is that I don't see a couple % improvement in combustion stats would be worth the extra expense and possibility of condensation damage.

heaterman, I guess I suspected that was going to be the case, well still not a bad position to be in, thanks for the advice

Yo, heaterman! Where can I get a full spectrum combustion analyzer like you must have used to test the Econo? I want something I can leave in the pipe that has either wireless or USB/Ethernet so I can continuously monitor my GreenWood?

And combining analysis with Viessmann . . . do you know what type of analysis is available to the user via on board display with the Viessmann wood gassification (200) unit? If it's anything like my oil unit, it's no doubt justifiable to spend the extra bucks.

Jimbo

What you'd want would be something on the order of a Testo 330, which will do 8 different fuels IIRC, including wood. It will download to a graphing program that comes with it. Runs on batteries or 110VAC. Be prepared to shell out a bit under $2K for a piece like this. Send me your contact info if you want one and I'll get you a firm price.

Having spent bucks on a GW install, and even bigger bucks on the Viessmann, I think my next 2 spot will be going to a buffer tank and a twin-coiled DHW tank so I can facilitate summer DHW production until I get solar. But what you speak of is close to what I want. I also want to be able to sense and record draft state, load door state, outdoor temp and barometric pressure. I'm not real big on it having its own graphing program as I want to be able to access the data ( and alter the controls) from my cell phone.