Why Water Comes From the Outdoor Unit in Heating Mode
Why the outdoor unit produces water in heating mode
When the air conditioner is heating your home, the refrigeration cycle is reversed. The indoor unit releases heat into the room, while the outdoor unit absorbs heat from the outside air.
To absorb this heat, the outdoor heat exchanger operates at a temperature below the surrounding outdoor air. When moist air passes across the cold outdoor coil, moisture in the air condenses on the coil in the same way that moisture forms on the outside of a cold drink.
| Operating condition | What happens outside |
|---|---|
| Mild or humid weather | Moisture condenses on the outdoor coil and may drip directly from the unit. |
| Cold weather | Condensation can freeze on the outdoor coil and form frost or a thin layer of ice. |
| Defrost operation | The system melts the frost, producing a larger temporary flow of water from the outdoor unit. |
What happens during the automatic defrost cycle
Frost reduces airflow through the outdoor coil and makes it harder for the system to absorb heat efficiently. To maintain performance, the air conditioner automatically enters a defrost cycle when its controls determine that frost removal is required.
| 1 | Frost forms: Moisture in the outdoor air freezes on the cold heat exchanger. |
| 2 | The system detects frost: The unit monitors operating time, temperatures and other control conditions. |
| 3 | Heating temporarily pauses: The indoor fan may slow or stop so that cool air is not blown into the room. |
| 4 | The outdoor coil is warmed: Frost and ice melt from the coil. |
| 5 | Water drains away: Meltwater exits through openings in the outdoor unit base. |
| 6 | Heating resumes: The system returns to normal heating once defrost is complete. |
What is considered normal
- Water dripping from holes or openings in the bottom of the outdoor unit.
- A brief increase in water flow during or immediately after a defrost cycle.
- Water pooling beneath the unit when no drain has been connected.
- Steam or mist around the outdoor coil during defrost.
- The outdoor fan stopping temporarily during defrost.
- The indoor fan slowing or stopping temporarily to avoid a cold draft.
- Clicking, refrigerant-flow or valve-change noises as the system enters or leaves defrost.
The amount of water varies with outdoor temperature, humidity, operating time and how much frost has formed. A unit may produce very little water on a dry day and considerably more water during cold, damp or foggy conditions.
When water may indicate a problem
Water discharge itself is usually normal, but the location or behaviour of the water may require attention.
| Observation | Recommended action |
|---|---|
| Water is creating a slip hazard or damaging nearby surfaces | Ask the installer to assess drainage and divert the water to a suitable discharge point. |
| Water is flowing toward the building, doorway or electrical equipment | Arrange for the installation and drainage route to be corrected. |
| A drain hose is fitted but water is backing up | Check for a blocked, kinked, frozen or incorrectly graded drain. An installer may be required. |
| Heavy ice remains on the outdoor coil and does not clear | Turn the unit off and arrange service, particularly if heating performance has reduced or a fault is displayed. |
| Water is leaking from the indoor unit | This is not explained by normal outdoor-unit defrost water. Stop the system if necessary and arrange inspection. |
| The unit repeatedly enters defrost but provides little heating | Check that the outdoor coil is unobstructed and arrange service if the behaviour continues. |
Drainage options
Outdoor units are generally designed so that defrost water can drain through openings in the base pan. Where this causes inconvenience, an installer may be able to fit a drain fitting, drain hose or other approved drainage arrangement and direct the water to a suitable floor waste or discharge point.
- Keep the area under and around the outdoor unit clear.
- Do not block the drain openings in the base of the unit.
- Ensure any drain hose falls continuously toward the discharge point.
- Avoid routing water across paths, stairs or other areas where it may create a slip hazard.
- In frost-prone areas, the installer should consider the risk of the drain or discharged water freezing.
Frequently asked questions
Water produced during heating or defrost is normally clear and odourless. Refrigerant is not discharged as a visible stream of water. A suspected refrigerant leak requires assessment by a licensed technician.
Cold and humid weather allows more moisture and frost to collect on the outdoor coil. Longer heating operation can also result in more accumulated water.
The system may be completing an automatic defrost cycle. Heating normally resumes after the frost has been removed.
No. These openings allow defrost water to escape. Blocking them can cause water retention, ice build-up or damage.