Tried the recirculating button in ‘the bus’ today ( 08 Expedition EL w/ rear heater ) and it helps.
The glitch ?
This truck has remote start and the recirc button is a temporary type circuit ( like the rear defog ) and does not stay preset for next time 
I only get the recirc feature once I’m in there.
bummer.
The thing to remember is to make sure you shut the recirc OFF before you park it for the night. If not, that frost/ice will be on the INSIDE of your windshield
I think the heater will put out warm air sooner on “recerculate” if the A/C is off!!!
I think the explanation is simple.
First, running the air conditioner puts a strain on the engine, making it warm up faster. The same thing happens in the summer, but in the summer you aren’t looking for heat, so you don’t pay as close attention to the temperature gauge.
Second, the heater effectively overrides the air conditioner. More accurately, the air gets conditioned before it gets heated. On a cold day, after your car is warm and putting out heat, turn on the air conditioner. The air coming out of the vents will be just as hot as it was with the air conditioner off.
The aptly named Tester is both conditioning and heating the air, and he is putting a strain on his engine to get it to warm up faster. He is adding additional strain on the engine by running the system in recirculate mode with the blower on its highest setting.
The additional strain on the engine probably isn’t doing any harm. The engine was built to withstand this kind of use, but I think that is helping him get heat sooner.
Cigroller; a heat pump is an air conditioner RUNNING IN REVERSE! A car air conditioner NEVER operates this way.
I agree the extra “strain” explanation has merit…I accomplish it similarly by driving up a steep half mile hill in second gear by necessity as soon as I leave the driveway. Car is warm by the time I reach the top, recirculate or no. Just like climbing a flight of stairs, nothing beats a good warm up at lower speeds, humanoid or car.
I think this is a function more of the recirculation door being closed rather than the air compressor being engaged.
The coolant bypass is going to be circulating coolant through the heater core from the second the engine is started and none of this coolant will be passing through the radiator at all. It will simply be a limited amount of coolant going in a circle until the thermostat starts to open; a very short circle.
Just my opinion anyway.