Can You Leave Your AC Unit In The Window During Winter? Essential Guidance For Homeowners

As temperatures drop, many homeowners wonder: Is it safe to leave a window air conditioner installed during the winter months? This article covers the risks, benefits, practical tips, and expert recommendations for keeping an AC unit in the window all winter. Learn how leaving your unit in place can affect your energy efficiency, home safety, and the long-term lifespan of your appliance—with actionable advice tailored for American homes.

Question	Answer
Can you leave your AC unit installed?	Yes, but it depends on climate, safety, and maintenance steps.
Risks of leaving it in?	Energy loss, drafts, water damage, security issues.
How to protect the unit?	Use covers, insulate gaps, regular maintenance.
When should it be removed?	Very cold climates, risk of snow/ice, security concerns.

What Happens If You Leave a Window AC Unit Installed in Winter?

Window air conditioners are designed primarily for warm weather, meaning their structure and insulation may not be suitable for harsh winter elements. Leaving one in the window during winter can allow cold air and moisture to seep inside, potentially damaging both the unit and your home interior.

If not properly secured, an installed window AC unit can lead to drafts, increased heating costs, and risk of mold growth. In extreme cases, components inside the unit may freeze, rendering it less effective or unusable the following summer.

Major Risks of Keeping Your AC Unit in the Window During Winter

Heat Loss and Higher Energy Bills

Window AC units often leave gaps around their frames, even when installed carefully. These gaps become weak points in your home’s insulation, letting cold air in and warm air out. This can force your heating system to work harder, resulting in increased energy costs and less comfort indoors.

Potential Water Damage and Mold Growth

When snow, rain, or ice accumulates around or inside your unit, moisture can seep into your walls and the appliance itself. Over time, trapped moisture leads to wood rot, peeling paint, and even mold or mildew, creating indoor air quality concerns and costly repairs.

Risk of Component Damage

Window AC components are not designed for sub-freezing temperatures. Rubber seals become brittle, metal parts contract and expand, and any leftover water inside the unit can freeze. All these factors increase the risk of permanent damage, especially to the compressor and coils.

Security Concerns

A window containing an AC unit is often easier to force open from the outside than a fully closed and locked window. This makes it a potential weak link in your home’s security, especially on lower floors or easily accessible areas.

When Is It Okay to Leave a Window AC Unit Installed?

Climate Considerations

In areas with mild winters—where temperatures rarely fall below freezing—and minimal snow or rain, leaving your AC unit in the window may be an acceptable choice. However, precautions are still necessary to prevent drafts and water leaks.

Building and Window Structure

If your window fits the unit tightly, and you have quality insulation materials to seal gaps, the risk of heat loss and leaks drops significantly. Some modern window ACs are designed with better sealing and weather resistance, making them more suitable for year-round installation.

Short-Term Cold Spells

If you live in a region where winter is short or unpredictable, temporarily leaving the unit in may be more convenient. However, this should never replace proper seasonal maintenance or weatherproofing.

When Should You Remove Your AC Unit for Winter?

Harsh, Snowy Winters

If your area experiences heavy snowfall, frequent ice storms, or prolonged sub-freezing temperatures, it’s best to remove and store the AC unit during winter. This prevents both appliance damage and moisture intrusion into your home.

Poorly Fitted Units or Drafty Installations

If you cannot fully seal the window around your AC—due to size, age, or window design—it poses a greater risk for heat loss and interior moisture. Removing the unit is the safer option in this case.

Security or HOA Regulations

Some neighborhoods, homeowners associations, or insurance providers may require window AC units to be removed at the end of summer for safety and community appearance standards.

How to Properly Leave Your AC Unit in the Window for Winter

Seal and Insulate Gaps

• Apply weatherproof foam or rubber seal strips around the unit’s perimeter.
• Use draft-blocking pillows or covers between the unit and the window frame for a tighter seal.

This simple step can save you a significant amount on heating bills and prevent cold air leaks.

Invest in a Quality AC Cover

External covers, specifically made for window air conditioners, can protect the appliance from snow, rain, and wind. Choose a cover that’s water-resistant and fits snugly, without blocking ventilation completely if recommended by your manufacturer.

Check and Maintain Regularly

• Inspect the unit periodically through winter for signs of moisture, freezing, or unwanted pests.
• Clear snow, ice, or debris from around the cover to prevent buildup and blockage.

Routine checks help you catch problems early and extend the unit’s lifespan.

Insulate the Interior Window Area

Use heavy curtains, thermal window film, or additional insulation panels inside to minimize any residual drafts.

Proper interior insulation further reduces energy loss and keeps your home warmer.

How to Remove and Store Your AC Unit for Winter

If you decide that removing the unit is the best option, follow these steps for safe removal and storage:

1. Shut down and unplug the unit. Let it sit for 24 hours to allow internal fluids to stabilize.
2. Carefully remove the unit from the window, following manufacturer and safety guidelines.
3. Drain excess water. Allow the inside to dry completely to prevent mold or rust.
4. Clean filters and exterior surfaces.
5. Store upright in a dry place, preferably covered to protect from dust and animals.

Proper seasonal storage ensures your AC will be ready and efficient for the next cooling season.

Best Practices for AC Unit Winterization

Task	Purpose	Recommended Frequency
Seal window gaps	Prevent drafts, save energy	Each winter installation
Use waterproof AC cover	Avoid rain/snow damage	Annually
Clean and check unit	Catch rust, mold, or pests	Monthly during winter
Insulate interior	Reduce remaining drafts	Each cold season
Remove/store if necessary	Protects in severe climates	Before first frost

Choosing the Right AC Cover for Winter

Investing in a high-quality cover is essential for protecting your investment. Suitable covers should be waterproof, UV-resistant, and fit snugly around your unit. Some feature additional insulation to further block out drafts.

Types of AC Covers

• Exterior Vinyl Covers – Block rain, snow, and ice from reaching the unit’s casing.
• Insulated Covers – Add a layer of padding to reduce heat loss and noise.
• Full Enclosure vs. Partial Covers – Choose based on accessibility and manufacturer instructions.

Never use materials that prevent air circulation if your AC design relies on some ventilation during inactivity, as this can lead to mold or rust formation.

DIY Insulation Methods for Added Efficiency

There are several DIY approaches to further insulate a window AC unit during winter:

• Fill gaps with weatherstripping (foam or silicone varieties preferred).
• Apply shrink-wrap window insulation film over both the unit and surrounding glass.
• Add interior draft snakes or thermal curtains as a barrier.

These strategies not only improve comfort but also safeguard your AC against cold-weather deterioration.

Expert Tips for Optimal Window AC Maintenance in Winter

• Clean or replace filters before closing the unit for the season to prevent the growth of bacteria and mold.
• Lubricate any moving parts as recommended by the maker—especially if storing the unit in cold conditions.
• Regularly check for pest activity, as unused ACs can attract insects or rodents seeking shelter.

Consistently maintaining your unit throughout the winter months can significantly extend its useful life and ensure efficient, problem-free cooling when summer arrives.

Frequently Asked Questions on Leaving AC Units in the Window During Winter

Will Leaving My AC Unit Installed Void Its Warranty?

Check your manufacturer’s warranty details. Some warranties require seasonal removal and storage to prevent exposure to harsh conditions, especially in cold climates. Not following these recommendations may limit your coverage.

Can I Leave a Portable AC Vent in the Window During Winter?

Portable air conditioner vents cause similar risks as window units: drafts, leaks, and reduced insulation. Remove and seal the vent during winter to maintain energy efficiency and prevent water intrusion.

How Can I Tell If My Unit Is Letting in Drafts?

On a cold or windy day, run your hand around the perimeter of your window unit. If you feel cool air or notice condensation, additional sealing or insulation is needed.

Should I Unplug My Window AC in Winter?

Yes. Always unplug the unit if it will not be used for several months. This prevents trickle energy drain (phantom draw) and protects the unit during power surges.

Is There a Risk of Freezing Pipes Near the AC?

If your AC allows significant cold air infiltration, nearby pipes or radiators may be at risk—especially in older homes with poor insulation. Ensure proper weatherproofing to avoid costly plumbing repairs.

Summary Table: Pros and Cons of Leaving AC Unit In Window vs. Removing

Action	Pros	Cons	Best for
Leave Installed	Convenient, no heavy lifting, can use AC during warm spells	Energy loss, increased bills, potential water or pest damage, security risk	Mild climates, tight installation, easy accessible upper floors
Remove & Store	Maximum energy savings, protects AC from damage, improves security	Extra effort, space needed for storage	Harsh climates, old/drafty windows, ground-floor units

Conclusion: Make An Informed Choice for Your Home

Deciding whether to leave your AC unit in the window all winter should be based on your local climate, your unit’s fit, and your willingness to maintain proper sealing and insulation. When in doubt, remove and store the unit for best results—but with the right weatherproofing, some homeowners can safely leave their unit installed with minimal risks. Always follow the manufacturer’s guidelines for care and warranty protection, and keep your home energy-efficient and comfortable year-round.