The Risks Of Sitting Your Outdoor AC Unit On The Ground

Charlie D Paige profile pic

Most outdoor AC units for a split AC system are positioned on a pad of some sort to elevate them off the ground. Is this really a necessary installation, or can you position the outdoor AC unit directly on the ground? We will cover whether this is an acceptable method or one to be avoided.

The risks of sitting an outdoor AC unit on the ground include leveling problems that can negatively affect the unit’s operation, potential flooding causing damage, and vegetation accessing the unit’s internal workings by growing up from underneath. Installation on a concrete pad is recommended.

If you need to place the aircon in a hurry or you are not sure of where to best position the unit, you may wonder why a pad is necessary at all for these units. We will share our insight regarding what is acceptable for the positioning of the unit and the risks and challenges associated with each method.

Can You Place Your Outdoor AC On The Ground?

An outdoor AC air con unit sitting directly on the ground
An outdoor AC air con unit sitting directly on the ground

Creating a support base for the outdoor AC unit can be an expense you did not bargain for when you ordered your AC installation. In desperation, you may be tempted to place the unit directly on the ground, thinking it will not do the unit any harm. They are designed to be installed outdoors, after all!

There are several good reasons why AC installers do not position outdoor AC units directly on the ground. If this thought is mulling over in your mind, we will help you dispel this idea as one not worth considering.

Risks For Placing An Outdoor AC On The Ground.

Even though the outdoor AC unit is designed to withstand the outdoor environment, we still need to take certain precautions to protect the unit and keep the installation stable.

Failing to take these precautions can result in an AC system that does not work efficiently and eventually becomes problematic.

The Outdoor AC May Not Be Level

Several large air conditioning (AC) units
Several large air conditioning (AC) units

An outdoor AC unit houses the compressor part of the system, and this assembly must be installed level. Most natural ground is not level to start out with, and even if you level the ground, it can subside under the unit.

Even if the unit was installed level initially, the unit’s weight could compress the soil unevenly below it, or rain can compromise the soil, causing subsidence. This will result in the unit being out of level.

When the outdoor AC unit is installed, you will find that the installer is meticulous about ensuring the unit is level. Why is this so important for this part of the equipment?

Some of the reasons why the unit must be level are as follows:

  • To allow for even flow of refrigerant and lubricant. If the unit is not level, refrigerant can accumulate or become trapped in certain piping sections. This will reduce the efficiency of the refrigerant cooling and the unit’s lubrication.
  • Prevent fan damage. The AC unit’s fans are finely balanced to operate at high speed. If the unit becomes off-kilter, the balance of the fans will be off, and it will cause unnecessary wear on the bearings.
  • Vibration damage. If the unit is not level, the vibrations caused by the operation of the machinery will magnify these vibrations. Excessive vibrations can damage pipes and tubing, seals, and joints and cause refrigerant and lubricant to leak out of the unit. This will reduce the efficiency of the AC and cause damage to the unit, which all translated to additional expense.

The leveling of the equipment is the primary reason the unit should not be installed directly on the ground, but it is not the only reason.

Flooding Of The Outdoor AC Unit

A flooded patio area due to improper drainage provision
A flooded patio area due to improper drainage provision

Even if the area where you live is not prone to flooding, heavy rainfall can produce localized flooding, even in your backyard, negatively affecting the AC unit.

Most of us have experienced minor flooding where heavier than usual rainstorms have caused temporary high water levels in our gardens. This is a problem for outdoor AC units if they are directly on the ground.

  • Flooding can cause soild to subside. The soil can subside or be washed away, resulting in the unit becoming out of level.
  • Electrical faults. Water entering the unit can cause electrical faults and even burn out the wiring.
  • Damage fan motors. Fans are important in these units for extracting the heat from the refrigerant. If water enters the fan motors, they will be damaged, resulting in costly repairs.

For these reasons, most installers elevate the outdoor AC unit to accommodate this type of occasional flooding.

Vegetation Growth Into The Outdoor AC Unit

If the outdoor AC unit is installed directly on the ground, it can become a problem with vegetation growth around and under the unit.

Vegetation growing around the sides of the unit can restrict the airflow for the efficient functioning of the unit. It also becomes difficult to trim around the unit with power trimmers without damaging its outer casing.

While pants outside the unit can be a nuisance, plants growing under the unit can be even more problematic. Grass and weeds can grow under the unit and enter the unit’s workings through vents in the unit’s casing or if the unit does not have a closed base.

These plants can become entwined in the pipes, tubes, and wiring in the unit’s inner workings. They will prevent efficient cooling by limiting heat dissipation and cracking or damaging refrigerant and lubricant pipes.

Best Alternatives To Setting Your Outdoor AC Unit On The Ground

Since the natural ground is not a suitable platform for your outdoor AC unit, what would the best alternatives be to provide the necessary stable and level foundation for these units?

Several options make suitable platforms for the outdoor AC unit, but some are better, more permanent, and more stable than others. We will briefly look at each type and present the advantages and disadvantages of each.

A Concrete Pad For The Outdoor AC Unit

An AC compressor unit
An AC compressor unit

A concrete pad is the preferred mounting platform for outdoor AC units. It will be the primary option recommended by most AC installers, and for good reason.

Concrete is strong, does not subside under the unit’s weight, and does not subside in adverse weather. A concrete pad will prevent plant growth into the machine, and it is easier to remove plant growth around the pad than against the unit.

The concrete pad can be built up to provide the necessary elevation to protect the unit from occasional flood damage. Concrete is easy to level when put down, and once it is level, it usually stays that way, making a great permanent foundation for the AC unit.

The main downside to a concrete pad is the cost and time required to install it. Some HCAV installers will install the concrete pad for you and include the costs in their price, while others may require that a different contractor be used to install the pad. Ask these questions of your installer when you place your AC order.

A Wood Pad For The Outdoor AC Unit

Wood is often used as an alternative base for the outdoor AC unit, and while this option may reduce the cost and time to put it in, there are some disadvantages to this material.

Wood is an organic material making it prone to decay. Treated lumber can be used, but it will only protect the wood for a relatively short time frame compared to the lifespan of concrete.

Wood is also affected by the weather and expands and contracts based on heat and moisture in the atmosphere. This can affect the leveling of the wood base, affecting the level of the unit itself.

The advantage of a wood base is the lower cost and faster installation, but the disadvantage is the lifespan of the base and the need for constant maintenance.

Cinder Blocks As A Foundation For The Outdoor AC Unit

Cinder block closeup
Lots of cinder blocks stacked on top of one another

Cinder blocks are a common alternative to a concrete base and can be a better choice than wood for the platform’s longevity.

Cinder blocks have a similar advantage to concrete in that they are robust and long-lasting. The advantage they have over a concrete base is that installing a cinder block base is cheaper and quicker.

Leveling a cinder block base is relatively easy, and once it is done, it is unlikely to move easily and disturb the level of the AC unit.

Another advantage is that it is not as permanent as concrete, so if you need to move the AC unit, you can relocate the cinder blocks with it rather than lay new concrete.

The disadvantage of cinder blocks is that the blocs can shift if the soil under them is unstable, resulting in problems for the AC unit.


Placing your outdoor AC unit directly on the ground is not a good idea, and it is not an acceptable installation practice for this equipment.

While it may be the cheapest and quickest option, you will quickly develop problems with this type of installation. In the long term, it is better for the unit and better for your pocket to pay the extra upfront cost and install an appropriate base for the outdoor AC unit.

Charlie D Paige profile pic
About Charlie D Paige

Charlie is a massive DIY fan, with dozens of DIY projects under his belt - ranging from tiling to electrics, and concrete pads to walls. Charlie loves tinkering, seeing how things works, the outdoors and playing with power tools... so is it any wonder that he's completed so many DIY jobs over the years?

Charlie loves spreading his hard-won DIY experience with the world via this blog.