Are BTU's a true common-denominator? Propane versus gassification BTU's

Usually a propane furnace produces less than NG.

http://profab.org/product.php?id=1

Output max

Why a boiler and not a furnace, like:
http://lamppakuuma.com/kuuma-vapor-fire-100-high-efficiency-wood-gasification-furnace.html

In a short answer, yes... a BTU is a BTU. But be careful about comparing peak BTU values vs. time rated values (ie. 8 hour burn). These time rated values should give you a much more realistic idea of how much usable heat will be produced. Also, caution that these values are always determined using optimal wood and loading the firebox to the gills...most likely unrealistic to be able to do all the time.

You also have to look at your entire heating system; however, and determine if you'll have more losses with a boiler, especially one outside. Any piping is going to have some heat loss...it's just a matter of how much piping will be required and how good the insulation is. Knowing your average heating load is great, but you really want to be sizing your boiler and other equipment for the peak loads. Being able to heat your house on an average day is easy...you want to be sure you can stay warm on the really cold days. Will your Nest give you those max/peak values?

1 BTU will raise 1 pound of water, 1 degree regardless of whether the source is wood, pellets, electricity or the neighbors backyard reactor.

There are 2 things to consider when looking at sizing of wood fired products.
1. How the manufacturer is obtaining the rating for their unit. (this is often difficult or even impossible)
2. The fact that no cord wood burner is capable of steady output like a gas or oil fired unit.

The first point is tough because of the variables in the fuel itself and the fact that recreating lab test conditions in the field is virtually impossible.
The second point is easily addressed by including thermal storage in your boiler system design. This allows a boiler sized to handle worst case conditions to function at or near optimum output even though the demand from the heating load is in many cases far less.

So the short answer....... don't be hesitant to go slightly oversized if your plan includes thermal storage. If it does not, I'd rather see the wood boiler handle about 80% of the house load and the last 20% be picked up by your normal heating source when needed. JMHO.....

I want one of those 'backyard reactors' you are talking about!

I got wasting time online, and found some really cool boilers with sterling engines attached. 50k Btu heat and 5kw electrical generation. One was made right in MI I think it was. I gave them a call. (would be perfect for the barn, make heat AND power on the days when the solar isn't producing.)

AHEM! 35 to 40k installed... WOw. But 95% efficient by burning the propane, then using the exhaust for the sterling engine.

JP

AHEM! 35 to 40k installed... WOw. But 95% efficient by burning the propane, then using the exhaust for the sterling engine.

Perfect illustration of the law of diminishing returns. Also known as "government work" as demonstrated by the Nazi's at EPA.

I would certainly pick the heatmaster over the empire. (I've seen both up close and worked on empire's) there's no comparison. the G 100 would probably be plenty. Disclosure: I'm not a dealer for either, but will be setting up with Heatmaster to be able to offer an outdoor option.

a rule of thumb for the G series boilers is that for an 8 hour reload time, they'll produce about half of the "max BTU" rating that is the 100,200,400 in the model number.
so the 100 will deliver 50,000 btu per hour averaged over 8 hours (assuming you're burning seasoned hardwood. if you are thinking about heating the shop too, I'd think about bumping up to the 200.

karl