Originally Posted by xenon
But the heater is still useful to demist windows quickly once you have the engine running. It would be unfeasible to expect it to noticeably "warm" the car though.
Agree, but as it does work fast(ish) for the initial demist, I see trying to use a timer for use ahead of the start, is one complex operation for possibly very little gain. Simply on the energy demands being so high. Any system to use it would still need battery protection, so can imagine it not working on the days you need it.
I noted on my 3-series that some winter cold starts there was definitely restrictions on the electrical system, rear screen demister and/or the auxiliary element would be clocked, it was a sign my car needed the battery on a trickle charge. I'm not talking of an old battery either, noticed the function when the car was relatively new. Shows how close we can sail to the wind on electrical demands during the winter months.