No Heat and It Is Below Zero: What to Do Right Now

What to do when your heat fails in freezing weather

1. Call for service

   Call a licensed HVAC contractor before you start troubleshooting, so a technician is already dispatched while you work through the checks. Say what the indoor temperature is reading and whether anyone in the house is elderly, an infant, or medically vulnerable — it determines how the call is prioritised.

2. Check the thermostat

   Confirm it is set to Heat, that the setpoint is above the current room temperature, and that the batteries are good. A blank or unresponsive display is very often just dead batteries.

3. Check the furnace switch and breaker

   There is usually a switch on the wall near the furnace that looks like an ordinary light switch — confirm it is on. Then check the breaker panel for a tripped breaker on the furnace circuit. Reset it once; if it trips again, stop and leave it for the technician.

4. Check the furnace door and filter

   Most furnaces will not run with the front panel removed or not fully seated, because a safety switch detects it. Reseat it firmly. If the filter is visibly loaded, replace it — a severely restricted filter can trip the high-limit switch and shut the furnace down.

5. Check your fuel

   On propane or fuel oil, confirm the tank actually has fuel. A tank low enough that vapour pressure drops in extreme cold can under-supply a furnace running continuously, which looks exactly like an equipment failure.

6. Protect the plumbing

   Open cabinet doors under sinks on exterior walls so room air reaches the pipes. Let a faucet on the most exposed run drip — moving water resists freezing. Confirm you can reach your main water shutoff. Keep the garage door closed if plumbing runs through it.

7. Conserve the heat you have

   Close doors to unused rooms, close blinds and curtains to slow radiant loss through glass, and keep exterior doors shut as much as possible. Gather everyone into one or two rooms.

8. Heat safely or leave

   Use only electric space heaters, plugged directly into a wall outlet and kept clear of bedding and furniture. Never use a gas range, oven, charcoal or propane grill, or any unvented combustion heater indoors — these cause carbon monoxide poisonings every winter. If the house is dropping toward the 40s and help is hours away, go somewhere warm and tell us the house will be empty.