Why Is My Heat Pump Leaking Water?

Is your heat pump leaking water all over the place? First off, that's bad. You should probably get some towels and a mop. Get that cleaned up. Second, why is a heat pump leaking water in the first place? What is going on? Are they supposed to do that?

Good question! And we have some good answers for you.

Causes of a Heat Pump Leaking Water

When we're talking about a heat pump leaking water there are two main components that we could actually be referencing. We could be talking about the interior air handler or the exterior condenser. Both can generate condensate that can build up and drip down or leak out or what have you. However, they will not do this during the same time of year. Generally speaking, the interior air handler should generate condensate during the summer when the system is cooling. Meanwhile, the condenser should generate condensate during the winter when the system is heating.

How A Heat Pump Works

Let's talk about what is actually happening when you use an air-source heat pump.

One key factor to keep in mind is that a heat pump does not create cold. That's not really possible. It doesn't create heat either. What a heat pump does is move heat from one area to another. Without getting into the mechanics of the process, all you really need to know is that to cool a building a heat pump removes heat and dumps it outside. To heat, a heat pump takes heat from outside and dumps it inside.

The major side effect of this process is dehumidification. In fact, dehumidification used to be the whole point. The process used today in air conditioners and heat pumps to control temperature was originally invented to reduce humidity in paper warehouses. Obviously, things have changed a lot since then.

Of course, the process of dehumidifying air creates condensation aka water. That water builds up on the coil of the heat pump or air conditioner. This is where your heat pump leaking water problem comes from. In an air handler, the condensate drips off the coil into a pan and then flows down a drain and outside. On a condenser, the condensate drips off the coil and onto the ground. It's fine. The ground doesn't mind.

Heat Pump Leaking Water Inside

A heat pump leaking water can be a major problem when it happens inside, because that's where all your stuff is. Modern systems are designed to keep any created condensate flowing outside, but that doesn't always work out like it should.

Condensate Drain Blockage

If you're having a problem with a heat pump leaking water inside, the condensate drain line is your prime suspect. Should this line get clogged the condensate build up in the drain pan will overflow. As such, the first thing you should check when you find an overflowing drain pan is that pesky drain line. Remove any clogs and make sure the water is flowing out smoothly. This will typically fix the problem.

Air Handler Not Level

A very different sort of leak can occur with a ductless mini split heat pump. Unlike a central air system, a mini split air handler is often mounted on the inside of an exterior wall. These rectangular cabinets contain the fan and coil and, of course, a drain pan. As with a conventional air handler, a mini split air handler drain line can get clogged, but that isn't the only reason you might find a mini split heat pump leaking water everywhere.

Mini split air handlers need to be installed such that they are as flat and horizontally level as possible. The air handler coil is positioned in such as way that gravity will pull any condensate buildup off the coil to fall into the drain pan where it can then flow out the drain line. When the mini split air handler is not properly level or flat against the wall that process is interrupted. In this case, the air handler must be properly leveled to fix the issue.

Heat Pump Leaking Water Outside

While a heat pump leaking water inside might be much more attention getting, the same condensate buildup occurs on the outside condenser when the unit is heating in cold weather. This happens outside your walls, so you usually don't notice. Typically, it's not a big deal.

However, it can be an issue in very cold weather, because we all know what happens to water when the temperature drops below freezing. Yes, that condensate that builds up on the outside coil can freeze, and it can freeze on the coil itself, Yes, this is in fact a problem. It's one of the reasons why traditional air-source heat pumps are not considered great low temperature heating systems. But it is a problem that can be solved.

Ice on the Coils

Heat pumps deal with ice build up on their coils by running a defrost cycle. Essentially, they turn on the air conditioning, pull some heat out of your house, and use it to heat the coil to melt the ice accumulation. If you're thinking, "Wouldn't that blow cold air into my house," you are on the right track, because that is exactly what it does.

As you might expect, this is not ideal for a lot of reasons. Which is why most air-source heat pumps also come with electric heat strips. These are backup, electric heat elements that can turn on to keep heating during this defrost cycle or to simply takeover when the outside temperature gets so low that a standard air-source heat pump can't keep up. Basically, you should always get a heat strip for your heat pump should you intend to use it very much in cold weather.

How to Stop a Heat Pump Leaking Water

A heat pump leaking water is a normal operation of the system. You just want to make sure that water is draining like it should to keep from causing water damage.

While there is no way to get around the condensate freezing problem of the heat pump condenser in the winter, the newest generation of heat pump units are getting much better at heating in cold weather. For example, the MrCool Universal heat pump can keep heating without relying on a heat strip in temperatures as low as -22F. Which is impressive.

Get More Help with Your Heat Pump Leaking Water

Is your heat pump leaking water inside or outside and you don't know how to fix it? Describe the issue in the comments below. We'll do our best to help you get to the bottom of the problem.

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