Glad we could be of help to you!
I wish to thank everyone who generously donated their time to helping me.
There was a weekend sale, so I devoted my Sunday afternoon to deciding what I'm buying. My best estimate of design heat load is 39k, using simplified online instructions for Manuals J and D. I can knock 6k off that figure by ripping off the siding, installing Typar wrap, and sealing leaks wherever I can find them. (I get 12k BTU/hr for infiltration at one exchange per hour, and should be able to modernize it to 0.5 per hour)
Manual D tells me that I can just barely move enough air through my current ducts to heat the house, assuming outlet temps 30° above interior temp. If my temp drop in the ducts is low enough to give me warmer outlet temps, so much the better. It turns out my 8x10 trunks are more of a limiting factor than my branches, and I don't want to pay for new trunk lines if I don't have to.
I will need to have return ducts put in the bedrooms. We're still arguing over whether to put returns in the kitchen/dining/living rooms, I think the central hallway return just off the dining and living rooms should take care of that, installer wants returns in every room but the bathroom/laundry.
I'm getting the GMH950453BX, a 20x25x5 media box, and a Honeywell 8110 thermostat, mainly because the 6xxx series lacks a 'circ' setting and I want to move air through the filter periodically. The GMH can be set for medium-low on the fan and it won't try to force too much air through the ducts. I was worried a GMVC would kick up the fan too hard.
A week from now, I should have the furnace sitting on a concrete platform in the basement waiting for my installer to hook it up. It'll be interesting to see how he handles the media box, but he said I could buy the 20x25 instead of the 16x25. (furnace has a 16x25 knockout on the side for return air)
Glad we could be of help to you!
tedkidd should read this. My tiny furnace putting out 39,800 btu/hr on propane is too big for my 1200 sq ft, 1970's ranch house in Michigan.
I'm living in the house, getting 30% run times (10 3/4 minutes out of 35) on low stage in darkness with a moderate breeze with thermostat set to 24° above ambient. That implies I could get about 75-80° above ambient from low stage, if it were possible to run this furnace for more than 12 minutes on low stage. Only other heat sources during the measurements were 350lb of humans and an energy star refrigerator. It looks like my actual load at 0° outside and 70° inside is closer to 28,000 btu/hr than my calculated 39,000 btu, and I should be able to drop that to around 20k with a few $hundred of insulation.
The only improvement I've made to the house to date is to seal the ductwork. That dropped my basement temps a degree or two, and added maybe two or three degrees to my theoretical ability to heat the house. It's still 64° in the basement with the house at 70°, and I've got three drafty single pane steel frame windows down there, with 140' x 2' of 8" cement block basement wall exposed to outside air. I'm surprised at how close to conditioned temps the basement is holding, just from the water heater, furnace, ductwork, and floor above radiating heat down there.
Last winter my DIY manual J calcs gave me 4400btu/hr for the entire roof (1200 sq ft, 70° design temp, R19) and 8400 btu/hr for the exposed part of the basement walls (280 sq ft, 60° design temp, R2).
I plan to increase the ceiling insulation to R38 and add R6 of foam sheet to the top 2' of the foundation, as well as insulate the joist pockets above the block wall. If my calculations above are correct, I'll save more from $100 worth of foam and glue than I could by taking the ceiling to R-infinity. Still, $250 worth of attic cellulose to drop my design load by 2200 btu/hr should be well worth doing when I'm paying $2.20 a gallon for propane.
A friend who's a block mason strongly recommends insulating the outside of a basement rather than the inside, says that by insulating the inside you can drop the wall temp so that the earth up against the wall can freeze and push the wall around.