Nominal BTU output

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zmender

Feeling the Heat
Dec 27, 2021
486
CT
Hey gang… trying to estimate the long term average BTU/hr that I’m asking from my stove.

my firebox is 2.5 cuf, but assuming that I can realistically load about 1.75cuft of wood in each time, accounting for existing ashes and void spaces.

now, assume about 25M BTUs per cord of hard wood. At 1.75cuft per reload, I’m putting in roughly 340k BTU during each reload.

Efficiency. My stove is rated for 76%, but let’s assume the operator (me) is an idiot and only burns moist wood, for a grand total of 70% efficiency. That means for the 340k BTUs I’m loading, I can realistically get 238k BTUs out.

burn time. I can get about 7hrs of useful heat per reload. Sure I’ve still got a bed of coals but my room temperature will stagnate/ drop. Pulling a number out of my ass, say I’ve extracted 85% of the 238k BTUs I’ve put in.

now for the grand total… 238*.85/7= 28.9K BTUs /hr that I’m getting from the stove. Does this math sound about right?
 
Start by weighing your fuel load. Don’t guess at volume or density. Weigh in the load. Time the whole burn. Then apply your efficiency factor.
 
This is a decent article on BTU's from wood stoves: