I was thinking about heaters on my long 14 minute drive home from work today. I'm probably missing something here, but why hasn't anyone used a small electric heater for use in the cockpit, rather than muffler shroud heat? Or has anyone? It would be instantaneous heat, no CO (I don't think... ), and easily installed in the baggage compartment or between the rudder pedals.
Sounds like a weight issue to me. Hot air that you're going to have anyway being connected to fairly light weight componants via scat tube Vs. the addition of a heater and fan system drawing power from a bigger battery getting charged from a heavier alternator.
It is all about current draw. A small electric heater you plug into the wall in your shop might be 500 Watts, a big one that uses most of the available current on a standard house circuit might be 1500 Watts. To get just 500 Watts on a 12 volt electrical system like in an aircraft would require about 40 amps. I suspect the amount of heat extracted the normal way with the muff exceeds 500 watts.