Why is there ice on my heat pump?

Ice on your heat pump is actually normal in certain conditions, but it can also signal a problem depending on how much ice there is and how long it's been there.

When ice is normal: During heating mode in cold weather, it's completely normal for a thin layer of frost or light ice to form on the outdoor unit's coil. Your heat pump is designed for this — it has an automatic defrost cycle that periodically reverses operation to melt the ice, usually every 30-90 minutes. You might notice steam rising from the unit during defrost, which is perfectly normal.

When ice becomes a problem: If you're seeing thick ice buildup covering the entire unit, ice that persists for several hours without melting, or ice forming during cooling mode (summer), that's a sign something is wrong. Common causes include a malfunctioning defrost control board, a failed defrost sensor, low refrigerant, restricted airflow from a dirty filter or blocked coils, or a stuck reversing valve.

In Ottawa's climate specifically, our winters are harsh enough that cold-climate heat pumps (rated to -25°C or lower) are strongly recommended. A standard heat pump struggling in -20°C Ottawa temperatures is more prone to excessive icing because it's working beyond its design limits.

On the safety side, a heavily iced unit that can't defrost properly will eventually stop heating your home efficiently — a real concern during an Ottawa winter. If your heat pump is running but you're not getting adequate heat, or the ice has been there for more than a few hours without clearing, it's time to call a technician. Don't try to chip the ice off manually, as you can damage the delicate aluminum fins on the coil.

Your next steps: Check that your air filter is clean and that nothing is blocking airflow around the outdoor unit (snow drifts are common culprits in Ottawa). If the ice clears on its own after a defrost cycle and your home is staying warm, you're likely fine. If the problem persists, Ottawa HVAC Pro can diagnose your defrost system and get your heat pump running properly — feel free to reach out for a service call.