Why Is My Heat Pump Covered in Frost?
You bought a heat pump.
Fall gets colder.
Then one morning you look outside and discover frost on the outdoor equipment.
Is something broken?
Not necessarily.
Some frost on an air-source heat pump can be a normal part of heating-season operation.
Why Does Frost Form?
During heating mode, the outdoor coil becomes cold while the heat pump gathers heat from outdoor air.
Under the right combination of outdoor temperature and moisture, water can condense and freeze on that coil.
A small amount of frost is not automatically a failure.
The problem is allowing enough frost to accumulate that airflow and heat transfer become restricted.
That Is Why Heat Pumps Defrost
Heat pumps are designed to periodically remove accumulated frost from the outdoor coil.
One common method temporarily reverses the refrigeration cycle so the outdoor coil warms and the frost melts.
Seeing the outdoor unit temporarily change behavior during cold, damp weather can be normal.
Why Is Steam Coming Off the Heat Pump?
During a defrost cycle, melting frost and temperature changes can create visible water vapor.
It can look dramatic.
That does not automatically mean the equipment is smoking or overheating.
If you smell electrical burning or see actual smoke, that is different and should be addressed immediately.
What Does Normal Frost Look Like?
A light coating of frost that later clears during normal defrost operation can be expected under certain weather conditions.
What deserves attention is:
- heavy ice covering much of the coil
- ice that never clears
- fan blades contacting ice
- major ice buildup underneath the equipment
- heating performance declining at the same time
What Can Cause Excessive Ice?
Persistent icing can involve several possibilities, including:
- defrost-control problems
- sensor problems
- airflow obstruction
- refrigeration issues
- drainage or installation conditions
The ice is the symptom.
The underlying cause still needs to be identified.
Keep Snow Away From the Outdoor Unit
A heat pump needs outdoor airflow during winter.
Keep heavy drifting snow and debris from blocking the equipment.
Do not shovel or blow snow toward the heat pump.
And do not chip ice off the coil with tools that could damage it.
Do Not Cover a Heat Pump for Winter
This is important.
A cooling-only condenser may sit idle during heating season.
A heat pump uses the outdoor equipment to heat the home.
It must remain open to airflow while operating.
Learn What Your Heat Pump Normally Does
Fall is a good time to become familiar with:
- normal outdoor-unit sound
- normal frost appearance
- what defrost looks like
- how the thermostat behaves
Then when something genuinely changes in January, it is much easier to notice.
Not sure whether you're seeing normal frost or a frozen heat pump?
Air Comfort can evaluate cold-weather heat-pump operation and help you understand what your system is doing.
Frequently Asked Questions
Is frost on a heat pump normal?
Light frost can occur normally during cold, moist heating conditions. The system should periodically remove accumulated frost through its defrost operation.
Why does steam come from my heat pump?
Water vapor can appear as accumulated frost melts during a normal defrost cycle.
When should I call about heat-pump ice?
Call if heavy ice does not clear, blocks airflow, interferes with the fan or is accompanied by declining heating performance.