Why Aux Heat Fails in January

Every winter, the same call arrives during the first serious cold snap: the heat pump is running constantly and the house is losing ground. And the auxiliary strips — the part of the system specifically designed for exactly this weather — turn out to have been dead for months.

A duty cycle that invites failure

Auxiliary heat strips are the most neglected component in a heat pump system, structurally rather than through anyone's fault. They sit completely idle through spring, summer and autumn. Then the temperature drops below the balance point and they are asked to carry a substantial share of the heating load immediately, from cold.

That pattern — long dormancy, then hard duty — is harder on connections than steady operation. Terminal hardware expands and contracts through the seasons, connections loosen slightly, and resistance builds at the joint rather than in the coil where it belongs. Heat concentrates at that point, and eventually something gives.

The failure itself may well have happened in October. Nobody notices, because in October nothing needs them.

Why it stays hidden

A heat pump on its own handles Ontario weather comfortably for most of the year. Through autumn the strips are barely called on, and when they are, it is briefly and the shortfall is invisible.

Then January arrives, the heat pump hits the limit of what it can extract from genuinely cold air, and the backup that was supposed to cover the gap is not there. The system is not broken exactly — it is doing its best with half its heating capacity missing.

Defrost makes it worse

There is a second symptom that shows up earlier if you know to watch for it. Periodically the heat pump reverses to melt frost off the outdoor coil, and while it does that it is actively cooling your indoor air. The strips are supposed to run during defrost specifically to temper the supply and stop cold air blowing into the house.

Dead strips mean that during every defrost cycle you get a blast of cold air from the vents. People generally attribute this to the heat pump being "not very good in the cold". Frequently it is not the heat pump at all — it is missing strip heat during defrost.

The ten-minute autumn test

This costs nothing and finds the problem while it is still an errand:

1. On a cool day, set the thermostat to emergency heat. This locks out the compressor entirely and runs on strips alone.
2. Raise the setpoint a few degrees above room temperature.
3. Wait a few minutes and feel the supply air.
4. Genuinely warm air means the strips work. Air that stays cool or barely warms means one or more strips are dead.
5. Set the thermostat back to normal heat. Emergency heat is expensive to run.

October is the right month for this. A dead strip found in October is a scheduled repair. The same strip found in January is an emergency call during the busiest week of the year for every HVAC contractor in the city.

Strips or sequencer?

Same distinction as any electric heat kit. If some heat comes through but not enough, individual strips have opened. If there is nothing at all on emergency heat, suspect the sequencer or the control circuit before assuming every strip died at once.

Our element versus sequencer guide covers testing that properly.

The bill nobody expects

One more thing worth watching. If your winter hydro bill jumps sharply, the problem may be the opposite — aux heat running far more than it should, usually from a thermostat staging setting or a balance point configured wrong. Strip heat is expensive to run compared to a heat pump doing its job, and a system that leans on it unnecessarily costs real money every month.