Those tubes you see are a Herman Nelson Heater which is a VERY high BTU heater that is standard kit in Canada in the winter. The heat from the external source is ducted wherever it's needed.
The heat can be put into almost any critical part of the aircraft when the temps are very low. As SASLess said, small Car Heaters are also used, just little electric ones, and they also do a good job when the temps aren't too extreme.
These tools are a must trying to get a 212 ready at -40C when it's been out overnight...
RH