…and they were standard equipment on all 3 of my Outbacks.
I normally only use the heated seats on really cold days, but if my back is aching, I will use that feature (on the low heat setting) even in the summer.
In a Volvo or a saab they’re known as Swedish bun warmers.
A heat pump (basically run the air conditioner in reverse) is a possibility.
Much more efficient then electric resistance heating.
can a heat pump actually produce heat when the ambient temp is -40*?
Why not have the evaporator coils heated by the engine exhaust?
The answer to that is No. The heat pump we had needed a backup system I think at 20 degrees. It was more efficient in our other home.
But then why not fan force manifold heat into the cab? There were after market manifold heaters for Ford Model Ts 90 years ago.
http://www.mtfca.com/discus/messages/118802/170577.html?1289686292
I think an engine block heater as someone has already suggested would be the best for the OP. Get one that replaces a core plug on the engpne and put it on a timer to come on hours before you leave the house. As a bonus it helps warm the engine on just you.
Manufacturers of small planes use “combustion heaters” to heat the cabins. I flew Piper Senecas for an air taxi company on Long Island. The plane had a heater that would burn fuel from the right engine. It was troublesome though, and expensive to maintain.
Electric grid heating could be done but not to the customers satisfaction.
The Cummins B-series engine has used electric grid heating for the engine intake air charge during cold start-up replacing the need for glow plugs. The heating grid draws 90 amps, the trucks use a 120 amp alternator. Automobile charging systems have been 120 amps and greater for years. This energy could be used to heat the cabin but customers would not accept the dimming of the headlights at idle associated with a high load item like this.
Air conditioning during hot weather draws 30 to 40 amps, this current can be used for electric heating during cold weather without any modification of the charging system but the amount of heat would only draw complaint, in sub-zero weather blowing 60F air would not be satisfactory.
Using waste heat from the exhaust for heat? Some hybrids have a heat exchanger in the exhaust system after the catalytic converter to heat the coolant for heat and to warm the engine.These things can be done but the cost to benefit does not seem to balance out.
Actually, if efficiency refers to the conversion from electricity to heat, nothing can beat a resistance heater, it is 100% efficient! I used to have resistance heat as a backup to a wood stove in one of my houses and had this discussion a number of times. The resistance heaters are 100% efficient in conversion but very costly to run in comparison to other methods of generating heat…Pretty sure this was your point but wanted to add for the sake of clarity.
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Cadillac SLR sports car… had DUCTed AC to the perforated leather seats. Oh, my, gosh, was that NICE! Felt like you’d poured a cold Coke in your lap without the sticky wetness. The thing was $80,000 new… not worth it just for the seats, but they were NICE.
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Heat pumps are effectively more than 100% because they move heat from the outside to the inside, in addition to the heat generated by electricity in the compressor.
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You’re absolutely right!
I had completely forgotten about the compounding effect from using latent heat in the ground/air.
I stand corrected!
In discussing topics like this it might help to remember the basics: heat propagates from a warmer body to a cooler body. Hot exhaust cannot absorb heat from a cooler gas. It can only warm it up.
AC systems work by compressing a refrigerant, removing the heat generated by the compression (compress matter and it releases heat energy), and then reexpanding it wherein it absorbs heat energy (cools), and feeding it through a heat exchanger wherein it absorbs heat. There’s no way to use hot gas to absorb heat unless it’s temperature is reduced to below that desiring to be cooled.
More fundamentally, “temperature” is simply a method of measuring atomic activity. A highly active atom can transfer some of its energy to a less active atom, in effect “warming” it, but it cannot cause a less active atom to become even less active (cooler). The more active atom will always stimulate the less active atom.
You already have ac AC system “running backwards”… your heater! Rather than removing heat from the cabin, it’s adding heat to the cabin. 
It’s using the exact same principle; transferring heat from a warmer fluid (coolant) to a cooler fluid (cabin air).
You guys would be surprised how many cars come with cooled seats now. You can even get them in Kias.
That’s huooooguh! Wait what??
Guess I gotta find a reputable Kia dealer! 
I suppose heated seats are a great idea, it just isn’t something I personally would be interested in.
Nor, for that matter, cooled seats.
I have to comment that back in '93 I test drove a Mazda 929 with leather seats. The dealer let me take it home. The wife was NOT pleased. Anyway, the next morning it was cold out and when my fanny hit that leather I swore I’d NEVER get leather seats! That leather sucked the heat out of my fanny like a supercharger sucks air from the intake system! I can see where leather seats would really need to be heated. And black leather seats would probably need to be cooled.
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Heated, yes. Cooled… Eh.
I have black leather in mine. They’re heated but not cooled. I’ve never really suffered for want of a butt-chiller.