I mentioned a few days ago that I was ordering the Polarwrap Warm Air Mask from Sierra Trading Co. It arrived today--in spite of a driveway so icy that the UPS driver hiked up the hill to deliver the package. (Our driveway is 600 feet long, and about 100 feet of elevation gain. Talk about commitment to the customer!)
My wife and I went out for a walk this evening--and it worked very well. It wasn't as bad this evening: 31 degrees when we left, and no wind--but I could immediately feel the difference. If you use the mask exactly as intended (breathe through your mouth in and out of the heat exchanger system), you indeed get air that is as warm as inside your house--maybe warmer.
Unfortunately, I can't get quite as much air in and out through my mouth as through my nose (perhaps because of Venturi effect increasing air speed), but still, it helped a lot. The walk we did up the old highway is a bit more than a mile--and it is a steep hill. There is about a 500 feet gain, and even with warm air, it was a vigorous workout. But at least my lungs weren't in pain and shutting down from the cold.
Another strategy that seemed to work was to pull the mask down so that I had my nose pointing at the heat exchanger port that is supposed to be in front of your your mouth. This enabled me to get nearly all the warming benefit of mouth breathing, with the extra air flow of nose breathing. Perhaps if it was substantially colder--such as when out hunting mastodons or saber-tooth cats--it would not be such a good idea. But at typical winter temperatures, this is a great victory in the battle against cold-induced asthma.
I remain convinced that anyone who drives somewhere that you might get trapped in your car by snow should have one of these in the emergency kit.