If you’ve invested thousands in a high-quality external air conditioning unit to keep your house cool in the summertime, you may be wondering if you should protect it from the elements in the winter by covering it. On the surface, it would seem to make sense to shield it from biting wind and an accumulation of snow and ice. You want to avoid costly air conditioning repair, and who doesn’t? In reality, the decision is more complex and in many cases you may actually do more harm than good by covering an external AC unit. Remember, while some circumstances warrant protection, an external air conditioning unit is built to withstand most weather conditions.

Before you enlist the help of a professional air conditioning service, it is a good idea to weigh the benefits of each covering option. In order to decide if covering your air conditioning unit is the right decision, it is important to consider several key factors such as the type of covering, the severity of winter in your area and the proximity to your house’s roof. With this simple guide to HVAC protection, you will be equipped to judge all the factors involved and decide if covering is the right way to protect your investment or not.

Why Not to Cover an AC Unit in the Winter


When temperatures drop and snow starts to pile up, all manner of crawling and furry fauna seek shelter. Covering your air conditioning unit, either with a tarp or a solid cover, will create a tempting home for squirrels and other rodents in the cold weather months.

Before you agree to provide free winter accommodations your neighborhood rodents, you should consider the very real danger that they can pose for an air conditioning unit. Apart from filling the unit with debris such as leaves and twigs to decorate their new home, they will chew the wiring and strip insulation from key components, such a Freon lines to make their nests. Although they will certainly appreciate the protection from wind and snow, you may not appreciate the destruction they will wreak on your HVAC system.

Mold and Mildew:

While rodents can cause clear, physical destruction that can disable your air conditioning unit completely, mold and mildew may actually present a greater danger.

Securely covering the air conditioning unit will trap air inside the unit and thus lead to a buildup of mold and mildew. Mold and mildew are both types of fungi, with mildew appearing more as a discoloration while mold can develop into larger structures if allowed to grow unchecked. Both represent a significant danger for breathing and their spores can cause serious allergic reactions, bad odors, headaches and life-threatening lung infections.

Mold and mildew can be difficult to clean and homeowners will often require the services of an air conditioning service to perform a professional cleaning after uncovering their external unit in the spring.

Moisture Damage:

Many people cover their air conditioning units to prevent moisture from damaging it, but just the opposite is often the case.

When covered, moisture from condensation can build up inside, unable to evaporate properly without an airflow. Even smaller amounts of moisture accumulation can lead to secondary problems such as rust, mold and in some cases, even damage related to ice-expansion.

External AC units were made for outdoor use and as such the manufacturers realized that they will receive both rain and snow. So ironically, the best way to protect your unit from moisture is to expose it to rain and snow.

Why to Cover an AC Unit in the Winter

Keep Out Debris:

Although external AC units are meant to withstand the weather, this does not mean that they will look brand new after a decade of harsh weather. Lawn debris may be blown in, paint will fade and rust may eventually develop in places.

If done properly, covering can help slow a general weathering of the unit to include paint and rust proofing as well as debris buildup. As mentioned before however, it is important to ensure that there is a healthy air flow through the unit and a regular cleaning to remove leaves and pine needles is a good idea.

Falling Ice:

For those who have their external AC units near a roof that experiences ice buildup, there is a danger that falling ice could cause damage.

Some professionals recommending using a piece of plywood can serve as a protective roof for the unit while at the same time allowing airflow. In fact, damage from falling ice is one of the more common causes of repair calls in the springtime.

If your external AC unit is far enough away from your house or you live in a climate doesn’t see much icing, this type of covering may be entirely unnecessary, but it does avoid the problems of moisture buildup, rodents and mold that other covers can cause.

Hailstorms and Blizzards:

Your average storm won’t affect an external AC unit but damaging hail storms and severe blizzards may. In this case, proving a temporary cover before a blizzard strikes is a wise move as it prevents snow from building up inside and damaging the coils.

Hail storms can be unpredictable and are not limited to the winter months, but if severe enough, the battering can have an impact on your unit. In the case of hail, a simple plywood cover that allows airflow is again your best bet.

Tips for Winterizing Your External Air Conditioning Unit

After weighing the pros and cons, you may decide to winterize your external air conditioning unit. If so, here are a few tips to take into consideration:

  • Employ a cover that allows for airflow. This will prevent rodent infestation as well as mold and mildew.
  • Remove debris from the coils of your condenser.
  • Leave a foot of coil exposed to ensure airflow. This will prevent moisture buildup.
  • Consider a simple, hardcover. This will defend against ice damage while allowing open airflow.
  • Remember to remove any cover before using the unit again in the spring.


The Bottom Line

It is true that you can buy aftermarket covers for external air conditioning units, but it is also true that the majority of air conditioning repair calls in the spring are from people who kept their units covered through the winter (source).

If you live in a cold and ice-prone region, it may be a good idea to cover up for blizzards and falling ice, but not in an attempt to keep out all moisture (an impossible feat). A simple wooden cover can offer better protection than a snugly fitting cloth or tarp cover.

If you live in a warmer climate, it is almost never necessary to cover your unit.

No matter what your coverage decision, be sure to allow for adequate airflow and don’t forget to clean debris from the unit. Air conditioning units add value to a home and with a few simple, common sense steps a homeowner can ensure that they last for many years to come without resorting to air conditioning repair services.