Why’s My Heat Pump Leaking Water Outside In Winter?

Heat pumps have a defrost cycle governed by a control board. When outdoor temperatures drop toward freezing and below the control board will call for defrost when certain conditions are met to reverse the unit into the cooling mode, heating up the outdoor coil and melting frost or ice of the coil.

The melting frost or ice is the water you see under your heat pumps outdoor unit.

Water Under This Heat Pump Is A Good Thing In The Winter

It could be concerning matter if you never see water dripping and ice accumulating under your unit. It’s closely related to temperature and humidity. The lower the outdoor temperature and the higher the humidity the more water you should see.

Think about a window air conditioner. Cold air blowing inside. Ever walk by a widow unit on the outside and feel the hot air? Imagine turning that window unit around and blowing the hot air inside the house. We have just created a simple heat pump.

But a problem just came up. When you want that heat in your home it’s going to be cold outside and the temperature of the air going over the cold coil which is now outside is getting much colder because of the outside air temperatures.

When the outdoor ambient drops near freezing and below the coil will begin to freeze over and the airflow through the coil will stop.

Somehow we need to defrost that ice. That’s what the water under your heat pump in the winter.

Should My Outdoor AC Unit Be Leaking Water?

About 8 out of 10 of my customers don’t understand the difference between a heat pump or an air conditioning unit. On the outside they look the same.

By all looks and appearances you can’t tell if this is an air conditioner or a heat pump.

To the left you are looking at an AC unit or cooling only unit. If you peer down inside past the motor and fan blade you can see a compressor and a small amount of copper tubing.

That’s about all that makes up a cooling only unit.

Their is only one slight difference between this unit to the right and the AC above.

Where the copper lines attach to the unit there is a third port for the technician to attach his gauges.

But, peering down inside past the motor and fan blade there is much more piping and valves to make this unit heat and cool.

Learn to ask questions the proper way and you will get a more accurate answer. It’s not is my heat pump ac unit leaking water. Now that you know there is a difference, say my heat pump outdoor unit dripping water or my ac’s outdoor unit is leaking water.

Which it is probably not leaking outside, but inside. Read on I’ll explain more thoroughly.

Should My Window Be Unit Leaking Water Outside?

This is a great question. The answer will help you understand why your heat pump outside unit leaking water. Whole house heat pumps, air conditioners or central HVAC systems and window units each have an indoor coil and an outdoor coil.

Basic Refrigeration Cycle

These two refrigeration coils have fans that move air through the coils. The indoor coil picks up the heat in the house and the outdoor coil dissipates that heat to the out of doors.

The compressor pumps hot high pressure refrigerant (Freon) into the outdoor coil against a metering device where the fan blows over the coil gets rid of the heat to the out of doors.

Maybe you remember cans of

Most window units are designed to just cool occupied space. When inside air is circulated through the indoor coil, the coil picks up the heat in the room and transfers this heat to the outdoor coil through the medium of refrigerant or what most people call Freon (a brand name).

That’s why you feel the much hotter air outside.

But because the inside of your home is above freezing the indoor coil doesn’t freeze up like a heat pumps outdoor coil in the winter. Instead it will create condensation.

That condensation is drained through tubing or channels along the bottom of the window unit to the outside and hence the constant drip you see coming out of the unit onto your flower bed or whatever is under the unit.

Are You Asking How To Fix A Leaking Heat Pump?

Now you are aware that a heat pump outdoor unit leaking water outside is a natural event. But questions have to be specific. In the summer when your heat pump is mostly in the cooling mode is it leaking inside?

Now you need to address a condensation leak at the indoor air handler or furnace. Specifically the indoor coil drain pan and drain line leading to either a condensation pump or drain line somehow removing that condensation from your house.

Depending on your level of maintenance and expertise of the technicians working on your equipment, several things could be causing the leak.

  • Drain line could be plugged
  • Coil pan rusted out or cracked
  • Low on refrigerant
  • Coil dirty or plugged
  • Filter too small or dirty
  • Not enough air flow

Drain pans under indoor coils have a tendency to get dirty and fill with grime and mold. This debris collects in the pan and can plug the drain hole.

Indoor coils can freeze up in the summer just like heat pump outdoor coils can freeze up in the winter.

This coil froze up because the home owner turned his thermostat to cool,set the temperature below 70 degrees on a warm day in the spring time and then left it run all night when the outdoor temperature dropped.

The air filter was also quite dirty, limiting the amount of airflow through the coil.

A Pool Heat Pump Leaking Water Can Be A Different Problem

Although a pool heat pump has many of the same parts as a residential air to air heat pump it has a different type of coil or heat exchanger to heat the pool water. Instead of a coil with a fan, it’s a coil with water to pick up the heat from the heat pump.

This heat exchanger can be a chamber within a chamber, one with refrigerant and the other with water.

Do a google image search for pool heat exchangers and get a look at the types of coils that do this function.

Because you would now have another coil with water you have another source for leaks.

Separating now what you’ve learned about other water leaking scenarios a pool heat pump leaking water outside unit in the winter is proper for it’s operation. Again it depends on temperature and humidity.

Heat pumps should be raised up off the pad to allow for drainage. The bottom pan in the outside heat pump unit has drain holes that need to be kept clear for proper drainage.


Heat pumps and air conditioners are different because of the functions they provide. Heat pumps heat and cool and an AC unit only cools.

Having a puddle of water under a heat pump in the winter is a good thing as long as the heat pump is raised off the pad to allow for drainage.

When a heat pump is flat on the pad and drainage is limited then ice can form around the bottom of the unit causing damage to the coil. Ice forming around the aluminum fins and copper tubing has a crushing effect that destroys the coil.

Keep your unit maintained properly with checkups from a qualified service company.

Chad Peterson

Chad Peterson is near 40 year veteran of the HVAC industry. "I like to explain heating and air conditioning problems in a way the average home owner can understand. "

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