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Test the furnace before the first sustained cold weather, replace or inspect the filter, clear the mechanical area, and make sure intake and exhaust terminations are free of snow or debris when applicable. Confirm carbon-monoxide alarms are working and know where the furnace switch and water shutoff are located. Do not cover vents, bypass safety controls, or use an oven, grill, or outdoor heater indoors. If the furnace fails or smells of gas, leave the building and arrange emergency help.
What to ask next
The right next step depends on the system, the urgency, and the building. Keep the model number, symptoms, age, and any previous service notes nearby when you request an estimate. A professional should explain the diagnosis or sizing basis in plain language.
When to bring in a professional
Use the callback form to describe the issue, or review HVAC services to find the closest starting point. For urgent loss of heat, see what to do in a cold snap.