As I've stated in other threads, winter driving is a major handicap of electric cars. When I try to run with electric cabin heating in my G2 volt, I have seen up to half of my power consumption go to heating. I get 1.X miles per kWh. Running an EV like this is not only expensive, it's horrible for the environment due to your long tail pipe. Let's just do a thought experiment and imagine that your local power station runs on gasoline (it doesn't, but it probably runs on either coal, natural gas, fission, or falling water. The average of all of these in the US is currently a bit better than gasoline). The power station is optimistically 50% efficient. Power transmission is 95% efficient. Car charging is 92% efficient. Let's just say that again, optimistically, 43% of the energy in that gasoline burned at the power plant gets to your drivetrain. This is about the same as an atkinson engine used in most modern hybrids. Driving around with electric heating most likely brings your effective gas mileage down into the 20's, and if it's very cold you might as well be driving around in a pickup truck or a suburban, because in order to heat your car with fuel burned remotely, you are losing over 60% of the energy content in that fuel.
There is another, much better way to heat a plug in hybrid car however, and it's called cogeneration. Cogeneration is when you burn fuel in order to produce mechanical work (or electricity) and then use the waste heat from that process for climate control. This makes a remarkable increase in the thermal efficiency of your engine. In europe, you can even get cogeneration units to heat your house; there is a small generator powered by oil or natural gas in your basement, and the coolant for that generator then heats your house. It makes a lot more sense than making electricity at the power plant because that other 60% of power that would normally be wasted is being put to use. While essentially all ICE cars use cogeneration for heating, they still expel most heat directly into the atmosphere because the heating requirements of an automobile cabin are several times lower than the amount of heat generated by an ICE to keep the car moving. The Volt doesn't work this way however... it only runs the engine long enough to heat your car, never opening it's thermostat to allow hot water to flow to the radiator. While it runs, it also recharges your battery, which means that you are effectively getting twice the bang for the buck compared to running in the summer.
If electric space heating was sensible and economical than most buildings would be heated this way. Boilers and furnaces are expensive to purchase, very expensive to install, noisy, space consuming, and require annual maintenance, but even despite all of those major disadvantages they are used for the vast majority of space heating in every part of the world. There is a reason GM chose to heat the car by running the engine and it's a very good reason. It is less expensive for the user of the vehicle and it is better for the environment. Unless your electricity is extraordinarily cheap as in QC Canada, you should never ever want to heat your car with battery stored electricity.
As an aside, I have been looking for a way to fool the car into thinking it's a bit colder so that I can engage ERDTT at a higher temperature. I usually want the heat on if it is less than 40f out, so I generally drive around in hold mode in this temperature range, again because it is less expensive to do so and because it's better for the environment.