Heat the room not the tank. Nothing replaces insulation. Moving back from Los Angeles to Toronto was a bit of a thermal shock, moving north to more rural Canada even more so, bone chilling compares to the mere bitter cold of that city on the lake.

Insulation is the key here. You can heat with a light bulb if your insulation is good enough. There are houses based on recirculating air throughout a building envelope sold that do this and up to as far north as the mason dixon line, require no additional heat in winter. Above that a 100W light bulb per room actually works until you get farther north by which time you'll burn a cord of wood per season, a tenth of what is normally needed. The name of the company is Enertia Homes and they have a web site.

Now, from the early war-ravaged fuel prices of the late 70s and on all sorts of building alternatives were looked at: rammed earth,cob, straw, SIP panels and so forth but little was done really in terms of new sources heating. Nobody managed to get a house to work in a cold climate without adding supplemental heat. You can make things more efficient but you can' not heat north of the mason dixon line.

Except for one guy, A mech eng prof at Rutgers built his wife a greenhouse in 1974 and hasn't had to add supplemental heat to this day. He simply uses a pump to pump the water out of the greenhouse, which is in a pond, and pumps it under the house where it stays for the night. In the morning its pumped out back to the greenhouse to be warmed by the sun again. To this day nobody's ever cracked this nut besides this clever fellow.

The most efficient for of adding heat is a masonry furnace, the "russian heater" contra flow furnace.

The most efficient insulation is also the most stable and maintenanced free of all the natural building techniques: cordwood masonry. You stack 2 foot lengths of old softwood, mortar the ends and fill the middle with sawdust. It's structural up to two stories, completely fireproof and inexpensive if you can access to 2-year dead softwood, which must be debarked before use. Saw mills don't now what to do with sawdust ad would happily give it away. Get dry stuff.

Straw is popular but needs yearly maintenance of the earthen plaster or water can get in and mold eats your walls. Although we've found building over 100 years old made out of both straw bale and cordwood masonry only the latter was still structurally sound, level, square, intact and livable.

The house in Rutgers that requires no heat: http://rs79.vrx.palo-alto.ca.us/interests/alt.energy/heat/none/.images/00-0-Copr_2016-David_Mears.jpg "When David Mears and his wife Dorothy put their house up for sale at the end of last year, it wasn't just the four-plus acres of beautiful woodlot land that made the property appealing. Nor were the five bedrooms or extra cabinet space in their roomy kitchen the most significant features. The main attraction was the fact that the couple hadn't paid their heating bill for more than 25 years - because they had not received one since 1980."

Richard Sexton, Nov. 2017