Since you have very cold conditions, why not do what the long hall truckers do and block most of the air flow in front of your radiator? A lot of big trucks have a radiator cover that can be folded and snapped to cover 90, 75, 50 or 25 percent of the radiator. This will enable your engine to warm up faster. You could put a plastic covering inside the grill in the winter season so it would not be visible. A second option is to put in a little higher temperature engine thermostat so the engine would run a bit warmer. You could also add some insulation to the input water line to the heater. I would also check the thermostat to make sure it is closing properly at the temperature that is stamped on it. How long does it take for the blue cold engine light to go out?