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[yoderheating]

Normally when people talk about large water capacity they are talking about three times the gal of water per 1,000 btu's. For example a Empyre 450 has 300 gal of water and a similar size furnace by Taylor has 800 gal.

[dirtdigger]

I"m curious about a few things, everyone seems to just be comparing water gallons, not really how the heat is distributed, so my question is, how can you compare only water gallons in the boiler, and not really worrying about things like, say for example, one boiler is hooked to a heat exchanger radiator where a fan blows through it, and another is hooked solely to infloor heat in the concrete floor of a shop or basement, wouldn't the infloor heat have more thero storage as some call it, than the one with just a radiator/fan setup or doesn't that factor into any of the equation?

Then don't things like piping distance's, total footage of piping and lastly how well insulated the heated building is, all factor into that equation somewhere.     

In theory, won't a small water jacket, and large water jacket use the same amount of wood to heat the save given space, once the water's hot and you discount the wasted heat at the end of the heating season, if these are taken out of the equation isn't about the only thing  left things like burn times and temp fluctuation.     

Then when do things like efficiency come into play, how is furnace efficiency calculated? 

[LittleJohn]

Dirtdigger, you are somewhat correct about the size of the water and the application it feeds are related.

So let me break this down to the best of my understanding, and others can argue if they want. 
Adding a larger water jack to a OWB does not necessarily increase any of the following: Efficiency, heat output or length of burn time.  What the larger volume does do is to help reduce the shocks (hot or cold) to water temperatures to you boiler.  But by adding a large volume of water you are also increasing the start-up timeof the system, because you will have to get the entire water jacket up to temp before you can ever start trying to pull heat off of it to heat structure.

**Point in case -> old man runs a CB eClassic 2400 (340g water jacket), CB requires a thermostat bypass valve (when water temperatures below 140f come out of boiler it gets returned, above 140-165 some is returned some is allowed thru to HX or radiant application, above 165f water go straight thru to HX or radiant).  So in the fall when he fires up OWB he has to heat up 340g of water above 140, then it finally makes it to HX & Mixing valve before going out into the slab (4000sf).  It can take up to a day or two to get the whole slab up to temperature, if my dad is not payign attention and gets the fire light a little late