real efficiency of eko 25?

[ihookem]

I have a heat loss calculator from builditsolar.com. Today I came up with a calc of 36,000 btu per hr. So I went ahead and weighed 45 pounds of dry wood and put it in the eko at 1:30. There was only coals left so I figure there were no real btus in the boiler. It took 7 hours before the boiler could not keep water temps @ 140 degrees which is the min. for usefull heat in a hx. The temp before I put in the wood was also 140. I figure 45 lbs of dry wood @7000 btu per lb =315,000 btu to keep the house @ 68 degrees. So I needed 252k btu but the wood put out 315k. So 252,000 btu divided by 315,000 btu =80% efficiency. Does this make sense? Have you ever figured your % efficiency? If so how did you figure it? Also, does anyone else know where I can find a heat loss calc online?

 

[Nofossil]

That's a reasonable approach, but there are a bunch of variables that heat loss calculators can't really take into account. Actual infiltration rates, wind speed, solar gain, heat input from electrical devices, insulation effectiveness and others are all best guesses, so actual heat load on a given day may vary quite a bit from what a heat loss calculator might predict.

If you have historical oil / gas consumption data, you can calculate your actual heat load for last year's heating season based on the efficiency of your fossil boiler, then see how much wood it takes to replace that fossil fuel. That approach probably yields a better overall number.

When I calculate my EKO efficiency that way, I get about 80%. Must be a coincidence ;-)

 

[ihookem]

Thanks nofossil, my eko must be burning properly. That's kind of why I did the test. I don't know of my gas use for my house cause I always burned wood though.

 

[Chris Hoskin]

based on our experience your 80% is a good real-world number.

 

[Nofossil]

There have been a few pretty intense discussions of efficiency. Heavy reading, but interesting to us hard-core geeks:

Discussion 1

Discussion 2

There are doubtless a few more.....

 

[jebatty]

I remember pouring over those posts at the time. A post of mine yesterday based on someone else's data indicated that 20% MC wood burned at flue temp of 400F delivers 6050 btulb to the "system," and the system wood include various heat losses from the boiler, flue and plumbing into their surrounding spaces. Efficiency.