What Carbking said!
Icing is a problem for me in the winter even with exhaust heat to the aluminum Offy manifold, at least till the engine warms up. It was a problem with the stock setup on the various Chev sixes I've had. One could take out the heat insulators in the winter but what a hassle. I found much less icing when I used an electric fan but then there were a host of problems with that. You would think that ethanol gas would forestall the icing but that doesn't seem to be the case. Once the thermostat opens the problem goes away in my case.
