I am starting to look into Geo, and I'm trying to sanity check the size of the system for Heating purposes, based on present fuel oil average usage. For reference, my pre-build room-by-room radiant heat load total was computed at approx. 35k BTUs based on a 6 degree F. outside temp., and if basement zone is added in (currently it is not hooked up), then add another 15k for a total of 50k-55k BTUs/HR (paper world). Here's how I did my calculation, please let me know if this approach is sound and also a reasonable way to sanity check paper calcs. My assumption here is that average fuel consumption per hour equates to a number of BTUs/hour, which is the heat loss. I observedusage of 150 gal per month during Dec 2010-Mar 2011, = approx. 5 gallons per day. Foroil-based systems, each gallon of fuel oil contains 139,000 BTU of energy. Myboiler has an 0.85 AFUE (efficiency) rating. 139,000BTU * 0.85 = 118,150 BTU per gallon. 5gallons * 118,150 = 590,750 BTU per day. 590,750BTU / 24 hours = 24,615 BTU (average) per hour. If the above is a reasonable way to compute the ballpark heat loss (25k BTUs based on my usage calc, 35k-55k room-by-room specs), then I'm expecting the Geo system to be sized according to the 25k-35k or worst case, max of 55k BTU loss, or in that vicinity. I'm not clear on how 25k BTUs equates to "tons", but in my first quote I was given a heat load of 5.4 tons - does that size square with my usage or the paper calcs? Thanks for any inputs including correcting my assumptions.