Dana, for cars the issue is fuel density moreso than efficiency, especially if size and/or initial cost are not hurdles.

Badger, the problem with slab math is that it matters whose model you use. Siggy's is a simplified model. Passivehouse has a much more complicated model. there are probably dozens of others. there is no doubt that there is significant variance in slab losses between even two buildings in the same town as site conditions can vary dramatically... losses from a house on top of a hill and one further down on top of the water table will not resemble each other closely. but how to calculate? how to know?

an extra inch or two of insulation has some ROI for sure and maybe enough to justify it... it's good insurance.


as far as heat sources I love heat pumps, but it sure matters whose electricity you are using. Pellets and wood I like too, but particulate emissions are a concern if widespread adoption came into play.

Rob: I totally get the cost and energy density issues with electricity as transportation energy, and PV-electric vs. biodiesel will never be an either/or for every transportation application. The energy density of bio-diesel is VERY good, but to make a barely double-digit percentage dent in just the current diesel use in the US with algae requires a pond roughly the size of South Carolina (with an SC annual insolation factor too.) It's no panacea or anything close, at more than 1/10,000 the sun-to-wheels efficiency of PV using current technology for each.

Even at the best theoretically-possible genetically engineered & optimize that only shrinks to about 1/1000 efficiency factor, which means it will never be more than a bit-player in the transportation energy equation. By contrast, PV-electric can at least theoretically provide a large slice of the pie using current technology, once the battery cost (more than energy density) problems get solved. It won't be a long-haul rural dweller solution, but it could fill a large share of the commuter vehicle market.

European-style modulating pellet boilers are pretty clean burning, and have real market penetration in Germany & Austria. That might be a real option for bugzee's radiant heating, if there are local vendors & support. It would almost certainly be cheaper to set up than GSHP, but the operating costs are probably higher. I'm not sure how the economics would stack up to a Daikin Altherma.

I recently went with a pellet stove from Quadra-Fire. They have a nice selection at reasonable prices. We went with the Classic Bay 1200, it was the most efficient one suggested by my HVAC contractor. I absolutely love it! It heats my great room almost instantly and I've noticed about a 30-40% decrease in my heating bill. If you have room for a free standing stove, they really don't require a lot of maintenance, or take up a lot of space. Pellets are extremely efficient and inexpensive compared to many other heating sources. Hope this helps and good luck.