Should You Cover Your AC Unit in Winter? HVAC Experts Weigh In

Cold air has arrived, and you might think it’s time to put the air conditioning unit to bed until spring. However, experts advise against it. Covering your air conditioning unit can lead to various issues like mold growth, rust buildup, and premature corrosion. It can also become a home for animals seeking shelter from winter weather. These pests may use the wires to build a nest, potentially causing electrical damage.

To help you prepare your air conditioning unit for winter the right way, our HVAC experts break down the reasons why you should avoid covering your unit during winter—and what to do instead.  

Why Covers Aren’t Recommended

Many contemporary air conditioners are designed to operate in all types of weather without the need for a cover. "They are often designed with components that allow ice and water to glide off naturally," explains Sean Hogan, CEO of Aventus Eco.

There are several reasons why covers can be detrimental to your air conditioning unit, and our experts break them down.

Covers Restrict Airflow

Airflow helps any moisture evaporate and dries the internal parts of your AC unit. "However, covering your AC unit for winter can lead to restricted airflow—especially if it is covered too tightly," warns Jason Spurk, owner of Spurk HVAC. "The lack of ventilation causes moisture to collect and can lead to rusting and premature wear."

Covers Encourage Mold Growth

Covering your AC unit traps moisture inside the system, which can lead to mold growth. Since there is no ventilation, it becomes a damp and dark environment where mold thrives.

"When you completely cover an air conditioner—particularly with material that does not allow air to travel through—you create a humid atmosphere beneath it," says Hogan. "Even when it's cooler in the winter, temperatures can fluctuate, and mist might occur. This retained dampness, along with the lack of ventilation, makes it an ideal environment for mold and mildew to flourish."

The development of mold may cause interior damage, which can be costly to repair. "It can also produce spores that can enter your home's HVAC system when you switch it back on, affecting the quality of the air inside," warns Hogan.

Covers Attract Animals

A tightly covered AC unit is a perfect shelter for animals. It has everything they need in winter—protection from wind and cold as well as insulation and wiring they can use to create a nest inside. "The tighter the cover, the better it is for mice, squirrels, and other small animals," says Kevin Goude, HVAC expert and the owner of First Choice Heating & Air. "Pests often create a nest inside because tight covers are windproof and trap some heat inside—two essentials for surviving the winter."

Unfortunately, these creatures are capable of causing significant harm. "They may gnaw on electrical lines, create nests that obstruct drains or circulation, or leave droppings that might harm components," says Hogan. "There have been instances where animal damage caused systems to entirely collapse, which may have been easily prevented."

Animal nests can do more than cause electrical damage. "They may also introduce unpleasant odors or even bugs into your unit, which is the last thing anybody wants to discover while attempting to chill their house in the spring," says Hogan.

Covers May Cause Accelerated Deterioration

Covers can trap humidity, which accelerates the development of rust and corrosion. "In snowy climates, they can become weighed down by ice and snow—causing bending or cracking that will later affect performance," cautions Spurk.

Covers Void the Warranty

Most modern AC units made by reputable manufacturers are designed to withstand harsh weather conditions, including snow, ice, and freezing temperatures, says Travis Arnesen, vice president of marketing at Service Experts. "Any damage caused by improper covering will automatically void most warranties," he notes.

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Covers Can Be Forgotten

What happens on that random hot day in the middle of fall or when that first truly warm spring day occurs? Customers tend to turn the AC on without thinking about the cover, says Randall Boutte, manager of HVAC technician training at HomeServe USA. "This causes a situation where the condenser cannot reject the heat from the refrigerant," Boutte explains. "The high temperature can damage the equipment severely or create refrigerant leaks. Some models are equipped with pressure safety devices—but not all."

Covers Trap Dirt and Debris

A cover can also allow leaves, dirt, and other debris to become trapped in the coils. "When spring arrives, this dirt can reduce the unit's efficiency and even make it work harder, resulting in increased energy costs and perhaps premature wear and tear," says Hogan. "It is critical for an AC unit's long-term health to maintain some natural airflow even when it is not in use in the winter."

How to Prepare Your Unit for Winter

Hogan suggests the following simple, effective maintenance steps to prep your AC unit for winter:

• Perform a complete checkup of your unit: First, cut off the electricity to your outside unit. Remove any leaves, sticks, or accumulated debris around the unit and inside the fins. To clean the outer coils, use a soft brush or a low-pressure garden hose. Check for visible damage, such as bent fins or damaged wire insulation.
• Examine the water drain pipe: A transparent drain ensures that no water accumulates within the unit, which is especially problematic when the outside temperature drops.
• Cut back any vegetation: Always allow at least 2 feet of space around your air conditioning unit on all sides. Cut back any trees, plants, or hedges so air flows through the unit properly and to prevent leaves and other organic debris from contaminating the unit.
• Winterize any outside taps: Check that exterior water sources are properly drained and winterized. Burst pipes might damage the environment surrounding your AC unit without your knowledge.
• Schedule a professional inspection: Have a qualified HVAC specialist conduct a yearly checkup before winter. They will inspect the quantity of refrigerant and electrical connections, examine for signs of wear and tear, and ensure that everything is in working order.
• Consider a "top-only" cover: If you're concerned about heavy ice accumulating on top of the fan, consider using a "top-only" cover made of waterproof, flexible plastic. This sits over top of the screen, protecting the fan motor and other components within from heavy snow and ice, while leaving the sides open for airflow.
• Remove any snow and ice: If there is heavy snow, gently clean it off the sides and top of your air conditioner, as snow and ice can restrict airflow, resulting in mold growth, moisture buildup, and decreased efficiency. When clearing snow off the unit, avoid using a shovel. Instead, use your hands or a broom to prevent accidental damage to the fins or other pieces.