The Hastings heating system was very much along the lines described by camlobe for aircraft of that vintage. Pilots Notes state that;-
"Engine exhaust heat exchangers, two on each engine, supply warm air for aircraft heating, drawing air from the intakes inboard of each engine. Additional cold air, which mixes with the hot air from the heat exchangers, is supplied from the intakes on each inboard engine. The proportion of hot and cold air is adjusted by mixer valves. The air is then circulated, by electrically driven fans, through ducts to the cockpit and cabin."
Those were the days! No doubt today such a system would be digitally controlled and the description would fill a volume (As that pertaining to my car radio does!).