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[Scott7m]

Well....   

Lets say your heat exchanger in your furnace is a 100k btu....   

Let's assume that it kicks on 20 times per day for 10 minutes each time...   Assumption only... 

200 minutes or 3 1/3 hours,  which would give you 333,000btu in your home...   

Your saying 42000 btu for your hot water.  That gives us 375,000btu that your using..

We have already determined you Could be producing around 800,000btu per day... 

Sooooo...  At this rate 46% of the heat your producing actually ends up being used and the rest is wasted somewhere in the cycle and up the stack...



You were dividing total btu's of wood put in, or available btu's, and dividing it by # of burns, that would be assuming 100% efficiency, and well, it's just not how we should look at this


Now, earlier before I did the math I said in this winter were likely using 1/3 or so as much wood as we soon will.  You were you needed 162kbtu per hour for your home but right now your only using about 16k btu per hour on average, in weather like we've been having it doesn't take a lot and I think from what I'm gathering your home is very well insulated and even in the coldest conditions  your home won't require near as much as you think....   

I'll be back after more calculations

[Scott7m]

Ridge, your saying you need 162k btu, are you thinking per day or what?  Because, it never made sense.

Most homes use 25k btu per day heating water, you assume 40 and that's probably right!  So, based on all calculations I can find a 2700 sq ft well insulated home in your area should require Between 32,000 and 65,000 btu per hour during the winter...   

Now the math is making sense'

I had already guessed we were at 1/3 winter load.   And that you were using 15k btu per hour, we know that, so the math makes sense that your only using 15k per day but could be as high as 65k btu this winter, average winter conditions would require about 45k btu which is my thoughts, and makes my 1/3 load, 1/3 of 45000, which is 15000 and that's exactly what your burning now...   

I feel these numbers are actually pretty close to reality

[martyinmi]

Hey Ridge-
 You know how I don't always agree with Scott, but he's right this time around. The difference between upper 20's at night and upper 30's during the day and single digits at night and teens during the day is like..well..night and day- especially if there are high winds involved. If your wood consumption ends up being anything like mine, you'll be going through between 2 and 3 times what you are burning now. I've went through a full cord in 25 days before, and thats with a 1700-1800 sq.ft. home and a gasser.
   On a positive note, though, the petroleum institute won't get a dime from you no matter how frigid it is outside. That satisfaction makes all the hauling, splitting and stacking well worth it.
   I really am impressed with your live stats. I've not been able to check on them and see your blower running yet. That is certainly a good sign.

[MTJAG]

This makes me feel a little better.  As I write this, the outside temp is -12 degrees and we had -3 degrees last night.  The high today was 13 degrees.  Last night I topped off my CB5036 around 10 pm and it was around 157 this morning at 6:30 and puffing with mostly ash left over.  I refilled it and left for the day.  Just got back in at 7:00pm and it again was mostly white ash.  I filled it again and will let you know what it's like in the morning.  BTW, this is not a total fill, but about 2/3rds full.  90% of what I am burning right now is aspen, with 10% pine.  Anyway, I recognize that aspen doesn't have the BTU's that hickory or oak has, but I am surprised about how much wood my OWB is burning with the restrictor plate in place.  Having said that, we have been having some cold spells that really suck the wood down.

[willieG]

wow minus 12..here in ontario canada we are having rain and today was about 40..tomorrow calls for 32 (0 in canada) for a high temp and staying firgt about there for 24 hours

[Ridgekid]

Scott-

Your assumption of a 100K BTU HX was right on.
162, 700 BTU was just a general number by adding my home requirements. (HX and DHWX) And that's if they operated at the same time, every time.
I don't disagree with any of your calculations.

I think my calculations were high. Here's why.
The green dragon only holds 196 gallons of water. (Plus what ever 230 ft of pex, a 100k BTU HX and 20 plate hold)
My burns only last 15 minutes. So with 6.5 burns that's only 1 hour and 37 minutes.
Out of the 118# I stocked Sunday, half took me into Monday (Today) until 7PM, 24 hours after I stocked it.

Recalculating, I think it was closer to 408,870 BTU produced Sunday. (62,903 BTU per burn).

Going back to your estimate I used 375,000 BTU (Which again, I agree with) With my recalculation, We could say I used 91.5% of the heat created and 8.5% is loss or went up the stack. I know what you (and others) are thinking-NO WAY. I have doubt it's that efficient too, compared to gasifiers.

What I do know is that I burned 1 cord of wood (as of this evening) in 47 days of operation. I can't believe 54% of that wood went up the stack! (sorry~)

There's got to be a better way to calculate this!

[willieG]

from what i read about these stoves, a non gasser is at best 60 percent efficient (or less)

[MTJAG]

Scott-

Your assumption of a 100K BTU HX was right on.
162, 700 BTU was just a general number by adding my home requirements. (HX and DHWX) And that's if they operated at the same time, every time.
I don't disagree with any of your calculations.

I think my calculations were high. Here's why.
The green dragon only holds 196 gallons of water. (Plus what ever 230 ft of pex, a 100k BTU HX and 20 plate hold)

Hey RidgeKid, do you have a cap on your stack, and if so, would that make a difference in efficiency?
My burns only last 15 minutes. So with 6.5 burns that's only 1 hour and 37 minutes.
Out of the 118# I stocked Sunday, half took me into Monday (Today) until 7PM, 24 hours after I stocked it.

Recalculating, I think it was closer to 408,870 BTU produced Sunday. (62,903 BTU per burn).

Going back to your estimate I used 375,000 BTU (Which again, I agree with) With my recalculation, We could say I used 91.5% of the heat created and 8.5% is loss or went up the stack. I know what you (and others) are thinking-NO WAY. I have doubt it's that efficient too, compared to gasifiers.

What I do know is that I burned 1 cord of wood (as of this evening) in 47 days of operation. I can't believe 54% of that wood went up the stack! (sorry~)

There's got to be a better way to calculate this!

[Scott7m]

Yea ridge, I think the btu calculation was spot on.  Because it does not matter how many times the stove cycles at all.  That does not change the btu amount you placed in the stove whatsoever.  Also you cant really calculate it by the # of btu created per burn because quite frankly it just doesn't work that way.

So in my opinion, your # of cycles is irrelevant and so is water capacity.  Were weighing wood and seeing and estimating how many minutes your fan ran over your known btu rating coil.

With all respect ridge, the % of 46% fell right in line with every other test I've seen from cb or a similar designed unit.  For example natures comfort non-gassers were at 75 percent eff with a test we now know was off at least 20-25%.

Your pound usage was right in line per 24 hour and everything, the math kinda fell into place.  Keep in mind ridge it's much cooler now than it was the first few weeks we were burning when it took only 4-6 pieces per 24 hours or less

[MTJAG]

wow minus 12..here in ontario canada we are having rain and today was about 40..tomorrow calls for 32 (0 in canada) for a high temp and staying firgt about there for 24 hours

Yea, the actual low at my house last night was -14 degrees.  We live at 8600' in the mountains of Colorado.  My OWB was out of wood this morning at 5:30.  During these cold nights, my OWB undershoots the 175 temp setting by about 8 degrees to 167 or so when it is burning.  Have you noticed that your's does that with below zero temperatures?  I have infloor heat and all my pumps are running in the house with the heat demand.

[Scott7m]

Oh and in regards to 91%, no gasser is getting that either.  The folks at Garn who have one heck of a gasser say real world numbers in there units is in the low 80's.  They burn over 2000 degrees

As far as a better way of calculating it, there is only one way.  Weighing your wood over 24 hours and figuring how many minutes your coil ran.  The hot water part isn't a big player and your estimate of 40k is fine.

If you think you can get over 55% eff with a natural draft unit, well, IMO you have the best one ever produced. 

If it makes you feel any better I crunched some numbers last night on my cousins hardy and only came up with 41% eff, he has some install issues to i think

[Ridgekid]

Scott-

I believe you. In fact it couldn't be 91%. Let's remember it takes 1 btu to raise 1 gallon of water 1*.  Which means on my 15 minute burns to raise 200 gallons of water 10* should be approx 16,000 btu each, right? So I actually made 104,000 BTU in 6.5 burns? I guess that don't make sense either If I used 375,000 BTU. 

Oh the drama! I will continue "counting" my wood estimating an avg of 12.5#'s per piece and maybe we can narrow this down.

The real test is forthcoming: http://www.anythingweather.com/current.aspx?id=48442

Oh BTW- I like Willies estimate of 60%. (or less)   

If we continue to work on this I think as time passes we might just narrow this down. I could start doing email pushes for when my air handler comes on. I won't be able to time it, but I would know how many times it did come on???

[gmviso]

Pardon the neophite question, but what is a "burn"?

[Ridgekid]

Every time the green dragon comes on to reheat water. = burn

[Scott7m]

Ridge, I urge You to continue but your not allowing for how many btu roar up the stack during a burn and there is just so many variables for heat loss not considered..

If you think we can ever skew the numbers enough to get your furnace to 60% eff we might be wasting out time.  It's just really hard to get to numbers that high, just be rest assured that whatever your getting is that much the power company don't get.

As far as your stove,
Im not knocking it one bit, there a very good unit, I just don't think the eff is anywhere near what your hoping to see.  In talking to other folks as well, they say that cb eff rating is between 46-54%.