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Why is It Important that the HVAC’s Outside Unit Sits Level?


There’s an old saying that in real estate, there are three things that matter most—location, location, location. Likewise, when it comes to HVAC, the three things that matter most are installation, installation, installation.

If not properly installed, even the best HVAC equipment cannot run efficiently or effectively. Poor installation can affect the reliability and lifespan of HVAC units too.

One of the many steps in correct installation of an HVAC system is making sure that the outside unit sits level. On some lots and buildings, this can prove to be a challenge and may require additional site preparation, but the extra work is worth it.

Let’s take a look at why it’s so important for the outside (condensing) unit to sit level.

Keep the Compressor Running Smoothly

Have you ever seen a warning printed on a refrigerator box that says you must keep the refrigerator upright, not lying on its side? That’s so the oil stays level in the refrigerator’s compressor instead of pooling or running off into the refrigeration lines.

The first and most important reason that the condensing unit must be level has to do with the oil in the compressor. In an air conditioner or heat pump, refrigerant circulates through lines and coils, transferring heat into or out of the building, depending on whether you’re heating or cooling.

As the refrigerant absorbs heat, it changes from liquid to gas—just like boiling water on your stove. The compressor “compresses” the gas, increasing the pressure so that the gas releases that heat and turns back into liquid.

The motor inside the compressor requires oil, just like the motor in your car does. If the condensing unit isn’t level, then the oil level inside the compressor won’t be level either. This can lead to one side of the compressor’s motor not being properly lubricated.

Ultimately, that can cause compressor damage due to the grinding of the motor’s moving parts. In the meantime, the lack of lubrication can cause the compressor to overheat and run less efficiently.

Keep the Oil Moving

Another reason that the condensing unit must be level has to do with the oil that mixes with the refrigerant. There’s always some oil that escape the compressor and travels with the refrigerant through the lines.

As long as the unit is level, this oil comes back to the compressor and gets redeposited where it’s needed. However, if the unit isn’t level, then the oil may separate from the refrigerant and end up pooling in the lines and coils.

Over time, this can lead to a shortage of oil in the compressor, causing damage and overheating. Additionally, oil coating the inside of the coils can make it harder for heat to transfer, decreasing the system’s efficiency.

Keep the Water Draining

Failing to level the outside unit doesn’t just cause problems with oil. If the tilt affects the drain pan, then water can pool in the pan instead of draining out properly through the drain line.

That pooled water increases the humidity inside of the unit. That can cause premature rusting and encourage the growth of mold. Ultimately, this can lead to decreased efficiency, coil damage, and costly repairs.

Don’t Get Shaken Up

Another problem caused by installing the outside unit on an uneven surface is an increase in vibration. When the unit isn’t properly supported, it will vibrate more.

Too much vibration increases wear and tear on the equipment. It can even cause refrigerant lines to come loose. Over time, this will shorten the lifespan of the HVAC system.

The uneven weight distribution and increased vibration can also cause sinkage, where the ground gives way beneath the unit and it literally begins to sink. That can also pull refrigerant lines out of the building as well as potentially causing other costly damage.

Watch Out for Shifting Over Time

While having your HVAC system professionally and correctly installed is the first step, it’s also important to make sure your outside unit stays level.

Water running off from the roof can erode the ground under your outside unit. Or the ground may simply shift on its own over time.

If you see these kind of changes and suspect that your outside unit may not be perfectly level anymore, don’t ignore it. Have the unit inspected before serious damage can occur.


It’s not always easy to make sure your HVAC system’s outside unit is sitting level, but it’s worth the effort. Correct installation of your HVAC system is an investment that will pay off in increased reliability, efficiency, and equipment life for years to come.

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