shawn.pinet.name

I've always been curious about how much propane I would have needed to offset the amount of heat that I'm generating from my stove.  So today since it's the last day of my vacation I tried to come up with a rough number.

What units are you using?

I have a physics background so units don't mean too much, but you have to be careful with them.  Since I have to pay by the litre, but many things are in BTU when it comes to heat, or BTU/hr. So here's what I have, it may not apply to everyone.   That's how I'll try to work things out to end up with pricing as it sits today. :)

The Equipment in the Lab

My stove is a Small EPA stove from Napolean which says it puts out 11,700 - 42,200 BTU/hr for softwood and 55,000 BTU/hr.  We burn at lest 50/50 hardwood (usually higher), but not at a high rate.  We see the blower come on around 80-100C (+60 from room temperature) so that would give an upper bound around 260-320C for that kind of BTU (the high end of our burn zone on our thermostat, so again seeming plausible).  If we take the range as being 100 - 300C we get  around 216 BTU/hr/degree of heat on the stove, which I'll make friendly at 200 (we want "close).  So we get 12,000 + 200 * ((avg)T - 100) as an easy formula, depending on how fast we are burning (T). 

So our typical temperature is about 150-200C or 22,000 - 32,000 BTU/hr, which feels right, or close to it.

How many BTU are in a litre of Propane?

From information that I found in a number of places (but best found at cogeneration.net) I found that there is about 24,200 BTU / litre for propane.  You can do the math if you want.  :)

My furnace is about 93% efficent, meaning I get about 22,500 BTU / litre from this propane.  I have an HRV and the fire place is in the basement, so I don't think there is much effeicency lost.

So you after all this, how many litres did you actually offset?

0.9 to 1.3 litres per hour of propane when the fireplace is going.  Makes you think about low and slow doesn't it?  I can also look at it as while making this post I've avoided burning another litre of propane.  Viva la revolution!

Extra Credit

Energy Values for specific woods