The Defrost Cycle
Why you can trust our content
We know the plumbing and renewable energy industry can feel overwhelming, especially with conflicting advice and outdated information online. That’s why we base everything we do on clarity, expertise, and trusted sources:
What Is a Defrost Cycle on Your Heat Pump?
When the weather is cold and damp, you might notice your heat pump making different noises, a change in airflow, water dripping from under the heat pump, or even see steam rising outside. This is usually just the defrost cycle, a normal part of how your heat pump works.
Why does it happen?
- As your heat pump extracts heat from the outside air, moisture can freeze on the outdoor unit’s coil.
- If too much frost builds up, the system can’t run efficiently.
- To stay efficient, your heat pump will occasionally reverse its operation for a few minutes to melt that ice.
What will you notice?
- The indoor heating may pause for 5–10 minutes.
- The outdoor unit’s fan might slow down or stop.
- You may hear different sounds, like gurgling or swishing.
- A cloud of steam may rise from the outdoor unit as the frost melts.
- Water may drip from underneath the heat pump.
Is this a problem?
Not at all, it’s a normal, automatic process. Once the frost has cleared, your heat pump will switch back to heating as usual.
When to call for help
Contact us if you notice:
- The outdoor unit stays frozen for hours.
- Your heating doesn’t come back on after a defrost.
- Defrosts are happening very frequently and comfort is affected.
In short: The defrost cycle is your heat pump’s way of keeping itself healthy and efficient in cold weather.
Related articles
Which option best describes your home?
At a glance
What Is a Defrost Cycle on Your Heat Pump?
When the weather is cold and damp, you might notice your heat pump making different noises, a change in airflow, water dripping from under the heat pump, or even see steam rising outside. This is usually just the defrost cycle, a normal part of how your heat pump works.
Why does it happen?
- As your heat pump extracts heat from the outside air, moisture can freeze on the outdoor unit’s coil.
- If too much frost builds up, the system can’t run efficiently.
- To stay efficient, your heat pump will occasionally reverse its operation for a few minutes to melt that ice.
What will you notice?
- The indoor heating may pause for 5–10 minutes.
- The outdoor unit’s fan might slow down or stop.
- You may hear different sounds, like gurgling or swishing.
- A cloud of steam may rise from the outdoor unit as the frost melts.
- Water may drip from underneath the heat pump.
Is this a problem?
Not at all, it’s a normal, automatic process. Once the frost has cleared, your heat pump will switch back to heating as usual.
When to call for help
Contact us if you notice:
- The outdoor unit stays frozen for hours.
- Your heating doesn’t come back on after a defrost.
- Defrosts are happening very frequently and comfort is affected.
In short: The defrost cycle is your heat pump’s way of keeping itself healthy and efficient in cold weather.