You are not going to get much heat out of an IC vehicle heater at minus 35C either, you can try the cardboard trick, but good luck getting a piece in there with today's cars.
Never had problem getting heat when it's -35 out, it doesn't take much longer to start blowing warm just takes a bit longer to actually warm up the inside of the car.
Same.
Our V8 Ram, little patriot jeep and anything else we have purchased over the past 30 years has warmed up & operated just fine in -40 weather....even on the occasional day it gets colder than that, I've not had to use a winter front of any kind.
Cars & trucks from the '70s & '80s certainly needed help with keeping warm....anyone else here old enough to remember the stick on frost shields we used to put on a vehicles side windows to keep at least part of them clear?
