Can Someone Explain the MAX BTU RATINGs?

[pms1]

QUESTION: Can someone explain the max btu ratings (cordwood) in meaningful (i.e, heating) terms?

BACKGROUND: I have been rlearned that there is little to no standardization in the rating processes for stoves regarding max btu, heating capacity (sq ft of house), etc. By contrast, the EPA efficiency standards are, so far as i know, standardized but they don't care about heat output but emissions. The stove store owner said to forget the heating capacity as there is no third-party certification and manufacturers just give conservative, accurate, or liberal self-assessments. He also said they are assuming one room and 8 ft ceilings etc. But, he said that MAX BTU RATINGS are meaningful.

True, max BTU ratings are influenced by weight, species and moisture content of wood place within so again we are not comparing apples to apples between manufacturers AND between stoves of a given manufacturer (as some reveal the weights of wood placed within and they are different... likely influenced by stove capacity).

I guess we can assume that the max rating is the manufacturer tossing in the best quality wood and in the largest volumes possible.... to, well... get MAX!

So REVISED QUESTIONs: How much of a difference (in terms of heating capacity that i mention above is elusive to measure) is, for example the following outputs from the following stoves? Is 60k to 97k a huge difference but 60k to 70k hard to notice? is 60k to 70k a bigger difference (in terms of feel) than 70k to 80k? is it really that arithmatic?

60,000 BTU of the morso 3610,
70,000 BTU of the jotul F50TL,
84,500 BTU from the Lennox Canyon ST310 and
97,000 BTU from the Pacific Energy T6 alderlea

My House: 2500 sq ft, about 2000 of which is essentially one big room with 22 ft ceilings (with fans). well insulated throughout. Huge windows everywhere (high-end doublepane). Prescott Arizona (6000 foot elevation, central AZ)... 20s at night in winter... can go lower... Lots of wind at this location. Stove basically near center of big room.

thanks all. trying to figure things out. some super helpful knowledge out in these forums.

 

[Hunderliggur]

You should never size your system by "heating capacity (sq ft of house),". Where is your house, what time of year is it, how is it built, what temperature do you want to keep it at, etc. At best, "heating capacity (sq ft of house)" gives you an "idea" of where to look.

As had been said on this forum many times, the first step in sizing a sytem is to determine your heat load in BTU/hr. There are calculators for doing this (The US Dept of Energy has ResCheck and there are others) or you can have a heating and cooling professional calculate it for you.

I am sure if we dig far enough, we will find that the BTU rating of the stove is specified as x% moisture content of y type of wood, n inch split, m inches long. The BTU rating will be the peak rating - the maximum output when all is running well. It does not included firing or run-out which are energy producing, but not peak, periods. nofossil recently posted what he ball-parks his setup's overall efficiency, I believe it was in the range of 60 to 75 percent of rated capacity. From my experience that is in the ballpark.

As for differences in ratings, 60K to 70K is about a 15% increase in output overall. You are gong to have an interesting time heating the 22ft ceiling (radiant at floor level will give you the most comfort, preferably a radiant floor). The heat loss (and feel) through your windows will be large, they are only R-5 at best. Do you have insulated window covering for when you do not have solar gain (like at night)? You current (I assume) forced air heat pump is probably very oversized to handle the worse case scenario invisioned by the contractor who installed it. They do not want to be callled when it is the once in 100 year deep chill and you are cold in the house. On the other hand, your existing mechanical system can handle whatever your selected burner is unable to produce.

Hope this helps.