Every October, Calgary homes start running their furnaces again, and many notice a furnace burning smell on day one. It's especially common on the first cold night of the season, when thousands of furnaces start up at once. In most cases it's summer dust burning off the heat exchanger, and it fades quickly. This Calgary homeowner guide from Purcell Heating & Air explains why fall start-up smells happen, how long they should last, and which smells mean you should switch the furnace off and call a technician.