The Defrost Function on your Heat Pump -
Have you ever wondered why your heat pump needs to defrost? Do
you find the process a little confusing and complicated?
This document answers some of the most common questions in a
straightforward manner to help any and every one get the absolute
best from your heat pump this winter.
What is the defrost function?
Defrost function is a feature on every heat pump and is deigned
to remove ice build-up on the outdoor heat exchange. This has
occurred during the heating process of the heat pump because the
outdoor part has been taking the heat and moisture from the
How can I tell if my unit is defrosting?
Most units will indicate defrost by flashing LEDs on the front
cover. This may be a red or green LED depending on the model.
Why does it need to happen?
If a heat exchanger is covered in ice the airflow is restricted
and therefore the efficiency of the heat exchanger is greatly
decreased. Ice on the heat exchange also acts as a thermal
insulation barrier preventing heat absorption. By defrosting the
heat exchange the efficiency is increased.
How often does it need to happen?
This really depends on the following factors.
- How cold/damp the air is around the outdoor unit
- How much work the unit is required to do, eg. Room insulation
or greater expectation to heat adjacent areas.
- If there are any mechanical defects with the unit
Assuming for now there are no mechanical defects - how
often would my unit be expected to defrost?
Most units will not check for a defrost requirement until at
least 45 minutes have elapsed from initial start-up. This period
should have given enough time to bring the room to temperature.
After defrost has started, how long should it take to
Defrosting function on most units is ended after a certain time
has elapsed OR the outdoor unit heat exchanger temperature has
risen sufficiently indicating that defrosting can be completed.
Defrost termination can occur within ten minutes.
If my unit is frequently defrosting, what could be
Regular and unsuccessful attempts to defrost an outdoor unit can
be a sign that the system is undersized for the area to be heated,
may have a mechanical defect or is suffering from lack of
maintenance. Refrigerant loss, coils blocked by dirt, restricted
airflow due to obstruction such as foliage or blocked filters are
all possible problems.
First, try cleaning the air intake filters to the indoor unit as
this may help to reduce the frequency of defrost and will help
improve product performance. Also check your unit is not set to a
fixed low speed as this will prevent the unit delivering full heat
capacity while it can. Adjust the fan setting to 'auto fan' as this
allows the unit to automatically adjust the fan speed and so the
output capacity will match the requirement. If the unit is the
correct size the fan will slow as the temperature rises. Turn the
heating on earlier in the day or leave it on in extreme cold
If none of this helps, we advise a visit by a heat pump
specialist to help diagnose the problem.
If my unit is undersized, what can I do to remedy the
The selection of any heat pump is the responsibility of the
installation contractor. If an error has been made with the
selection, your redress lies firmly with the contractor. Equipment
is not at fault if it has been incorrectly sized for the
Is there anything I can do to decrease
Your heat pump will need to defrost less and use less energy in
a well-insulated room. Keeping the doors and curtains closed will
help. Insulate your floors and ceiling if they aren't already.
*Please note, these answers do not cover specific on any
particular model, therefore some small allowances should be made
for minor technical differences between units that can affect the
way defrost is both initiated and then terminated.