A Midwest homeowner who uses a detached garage for woodworking and a golf simulator asked Reddit for advice after realizing that leaving a window AC in place through the winter could make the space drafty, but removing it would also mean dismantling a custom frame built to hold the unit in the window.
Here's what to know
In a thread on r/DIY, the original poster said the AC "doesn't fit the window opening all that well," which is why a custom support frame was needed. Since the window cannot be closed without removing that framework too, pulling the unit for winter would be a much bigger job than a routine seasonal task.
Rather than tear everything apart, the poster asked whether it would be a mistake to leave the unit installed through the winter and mentioned possible ways to cover it, including a tarp outside and plastic wrap inside.
"I'm just trying to work through the pros & cons," the poster wrote.
Replies generally said the unit can stay in place, but many warned that an exterior cover may cause other problems.
"I leave my window unit in the garage year round and skip the outside cover entirely," one commenter wrote. "The AC covers trap moisture inside and that water freezes on the coils all winter in the Midwest."
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For many commenters, the bigger issue was preventing air from getting in on the indoor side. Several suggested using rigid foam board, foil tape, or a removable insulated box inside to keep out wind and dust.
More background
Many people use detached garages, porches, and workshops as hobby spaces without fully insulating or heating them. In setups like these, even a small gap around a window AC can let cold air rush in, making the area less comfortable and more expensive to warm when needed.
A tighter seal can reduce drafts, help keep out bugs and wind-driven snow, and cut down on wasted heat if the garage is occasionally heated for projects or exercise. It can also spare owners the cost and frustration of removing and reinstalling a bulky unit, particularly one built into a custom frame.
At the same time, commenters noted that the wrong fix could create another problem. If an exterior cover traps moisture, water can freeze on the coils over the winter, and it may create a sheltered place for pests.
What can be done?
Across the thread, the most consistent advice was to seal the interior side rather than the exterior.
One commenter said they use "a garbage bag and tape over the plastic wrap" to stop air from moving through the frame.
Another common suggestion was a more durable, reusable cover.
"Get a sheet of 4x8x1" thick rigid foam board and cut out a box that fits around the AC. Glue the pieces together, then tape over the seams with foil duct tape," one user wrote.
Another said they had reused the same foam-board cover for about five years.
That kind of fix could save money in several ways. It may reduce heating losses in a part-time workspace, help avoid replacing a unit damaged by trapped moisture, and eliminate the recurring labor and materials needed to remove and rebuild a custom mount every season.
Where can I learn more?
These articles look at questionable AC add-ons, drain cleaning, central-air airflow, and dry-mode savings.
• In Florida, HVAC pros gave a hard pass to a viral AC saver.
• A homeowner's TikTok showed how a simple drain cleaning can boost AC efficiency.
• A local news check found that closing doors in your home may not cut AC costs.
• A frugal homeowner said AC dry mode really helps curb mold and lower bills.
• A sustainability expert kept using dry mode all summer to trim cooling bills.
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