How to Seal a Window Air Conditioner for Winter (Remove vs Cover)

The best winter seal for a window air conditioner is to take the unit out, close and weatherstrip the sash like a normal window, and store the AC upright in a dry place. If you leave it installed, sealing helps — foam side-panel gaps, an interior insulated cover, and sometimes an exterior weather cover — but those steps only reduce drafts. They do not match a closed window for heat loss, and the cabinet still leaks outdoor air unless you seal the indoor face completely. ENERGY STAR says the same thing: at the end of the cooling season, remove the room AC if you can; otherwise use an appropriately sized winter cover.

I’m a homeowner who reseals his own window units each fall, not a licensed HVAC tech. What follows is checked against Frigidaire, LG, and GE winter-storage guidance, ENERGY STAR savings tips, and the U.S. Department of Energy’s Building America homeowner guide on window-AC air leakage. Your model’s manuals win when details disagree.

This guide was substantially rewritten and re-fact-checked in August 2026.

Key takeaways

• Remove when you can. Frigidaire’s winter-storage guidance is remove, then carton or plastic cover, upright in a dry spot. ENERGY STAR and DOE likewise prefer removal to cut winter heat loss.
• Leaving it in is Plan B. GE says removal is not a necessity — especially for heavy units and built-ins — and allows covering larger units left in place. LG’s winterize page walks through cleaning and covering a unit that stays in the window.
• Seal the room side hard. DOE’s Building America guide: after cooling season, remove the unit or seal it completely on the inside — otherwise air leaks through the unit itself.
• Covers ≠ removal. An interior insulated cover plus foam side gaps beats bare accordion panels. An outdoor cover mainly sheds snow and debris. Neither restores a closed, weatherstripped window.
• Moisture is the quiet risk. Sealing a damp unit or trapping indoor humidity against cold metal invites condensation and mold smell by spring.
• Two-person lift. Unplug first; don’t fight a second-story install alone from a ladder.

What the manufacturers actually say

Brand pages disagree on emphasis — remove vs cover-in-place — which is why the table matters more than a universal rule:

Source	Winter preference	Practical takeaway
Frigidaire winter storage	Remove carefully per the install instructions; cover with plastic or return to the original carton; store upright, dry, preferably off a damp floor	Treat removal + dry storage as the default Frigidaire path
GE Appliances — winterizing / storage	Removal is not a necessity; smaller models can go to attic/basement if you choose; large or built-in units may stay; keep stored units upright; covers protect from snow and ice	OK to leave heavy units in place; still unplug; never store on side/back long-term
LG USA — How to Winterize Your A/C	Power off and unplug; clean debris, coils, and filter; dry completely; waterproof cover with vinyl tie-downs; check for snow/ice through winter	LG documents a leave-in-and-cover winterize path
ENERGY STAR room AC tips	If possible, remove at end of cooling season to minimize heat loss; or use an appropriately sized cover	Efficiency framing: removal first, cover second
DOE Building America window-AC install guide (PDF)	Remove or seal completely on the inside after cooling season; otherwise air leaks through the unit	Indoor-face sealing is required if the chassis stays

DOE’s Energy Saver maintenance page (archived; live energy.gov path currently 404s) puts the same fork in one sentence: in winter, cover or remove and store your room air conditioner. For day-to-day weather, seals, and rain behavior while the unit is installed, see our window air conditioner care guide — this page is the winter leave-in vs pull-it decision.

Option A: Remove the unit (best for leaks and efficiency)

This is the answer when you care most about heating bills and a tight window. ENERGY STAR notes that a poorly installed room AC can leak as much air as a roughly 6-square-inch hole. Leaving that path open all winter dumps heat outdoors. Pulling the chassis lets you close and seal the sash like any other window.

1. Unplug. Do not rely on the remote or a timer. Pull the cord from the wall outlet.
2. Clear the room side. Lay towels on the floor — condensate often drips when you tip the unit. Have a second person ready before you loosen hardware.
3. Reverse the install. Follow your model’s removal section. Typical double-hung installs: remove sash lock / L-brackets, pull accordion or foam side panels in, raise the sash, and lift the unit into the room while keeping it as level as you can so the pan doesn’t dump indoors.
4. Clean before storage. Wash the filter; wipe louvers and accessible coils; let everything dry. Bagging a wet unit is how you get a musty first run in May.
5. Store upright. Frigidaire and GE both want the unit bottom-down in a dry place. GE adds: if it sat on its side or back more than a day, leave it upright and unplugged 24 hours before powering it again so oil can settle. Original carton is ideal; otherwise a plastic sheet over a dry, upright chassis.
6. Close and weatherstrip the empty window. That closed sash is the efficiency win covers never fully deliver.

Skip removal only when the unit is too heavy for a safe two-person lift, the opening is a fixed through-the-wall sleeve, or you truly have nowhere dry and upright to store it.

Option B: Leave it in and seal (practical how-to)

If the chassis stays, treat sealing as three jobs: stop side and sash leaks, block airflow through the cabinet on the room side, and protect the outdoor half from weather without creating a water trap.

1. Unplug and clean first

LG’s winterize sequence: power off, unplug, clear debris, clean accessible coils and the filter, and let the unit dry completely before you cover anything. Sealing over wet metal invites odor and corrosion.

2. Fix the foam side-panel gaps

Accordion filler panels are thin plastic with foam edges — draft machines in winter wind. DOE’s Building America guide recommends replacing those side fillers with rigid foam cut to the window channel (often about ¾–1½ inches thick to match sash depth), plugging the tops of the side channels, and taping joints. Closed-cell backer rod between the upper and lower sash beats the skinny foam strip many kits include for the meeting rail.

If you keep the stock accordion panels, expand them fully, add foam weatherstripping where light shows, and tape obvious seams. Do not caulk drain holes or outdoor louvers shut — winter sealing happens on the room side and at the window perimeter.

3. Interior insulated cover vs exterior cover

Cover type	What it does well	What it does not do
Interior insulated cover (quilted or foam board over the indoor face)	Blocks the biggest winter draft — air through the chassis into the room. Matches DOE’s “seal it up completely on the inside.”	Does not weatherproof the outdoor half; does not equal a closed sash.
Exterior weather cover (slip-on / waterproof with straps)	Sheds snow, ice, and debris; matches LG’s waterproof-cover-plus-tie-downs steps and GE’s cover advice for units left outside.	Does little for room-side heat loss alone; a poorly fitted wrap can trap moisture.
Plastic sheeting + tape alone	Cheap indoor draft block in a pinch.	Easy to seal moisture in; tears in wind; not a substitute for foam side seals.

My honest read for a leave-in unit: prioritize the interior seal. Rigid foam or a fitted indoor insulated cover over the grille, taped at the edges, does more for your heating bill than an outdoor sock with nothing on the room side. Add an exterior cover if you get driving snow or ice and your brand allows it — LG does, with periodic checks to clear snow off the top.

Do not run the air conditioner with any cover on. Unplug so a warm spell cannot start a covered compressor.

4. Tape and plastic — helpers, not the whole plan

Painter’s tape or foil HVAC tape can hold foam panels and seal the top and bottom of the chassis to the sash (DOE notes less-aggressive tape on painted frames). Plastic film over the indoor face works as a temporary draft layer if you can still check for condensation. Avoid wrapping the outdoor chassis cling-tight with no drip path — water under a sealed tarp stays there.

Skip the aluminum-foil-as-winter-armor tip from older DIY posts. Foil does not weatherproof the unit and is not a brand or DOE storage step.

Condensation, mold, and when not to leave it

A sealed-in-place window AC sits half in heated indoor air and half in outdoor cold. Warm indoor moisture that hits cold metal can condense. Bury that moisture under foam board or plastic and you can get staining, musty smell, or mold on the filter and grille by spring.

Reduce the risk: start bone-dry (filter washed and dry, coils wiped, no standing water in the pan); prefer a removable interior cover you can peek behind after the first hard freeze and after thaws; if you see beads of water or smell mildew, pull the indoor cover on a dry day, wipe, and improve the room-side seal rather than adding more plastic. In humid, mild winters — or if the unit already smells musty — removal and dry storage is cleaner.

Do not leave the unit in when:

• You can safely remove and store it upright — still the efficiency and moisture winner.
• The sill, brackets, or sash hardware are rotting, loose, or undersized. Winter wind loads a cantilevered chassis hard; a failing support is a fall hazard, not a sealing project.
• That window is a bedroom egress path. Blocking a required emergency exit for a draft fix is the wrong trade.
• Your manual’s winter section insists on removal and you have storage space.

Ladder and lift safety

Most injuries on this job come from dropping a heavy unbalanced chassis halfway out a window — not from foam tape.

• Two people minimum for anything you cannot cradle comfortably to your chest.
• Unplug before you loosen brackets.
• Don’t uninstall from a ladder outside. Bring the weight into the room. CPSC outdoor-repair guidance covers a helper spotting the ladder and stable footing — hauling a window AC from outside is the wrong job for that setup.
• Upper floors: if you cannot stage a safe two-person indoor lift, hire help or seal in place.
• Keep the unit supported until the sash and brackets are ready — never remove the last screw while the chassis can tip outdoors.

When to call a pro

• Through-the-wall / sleeve units not meant for seasonal pull-out, or mounts that need reframing.
• Rotten sills, cracked masonry around a sleeve, or outlet problems (hot plug, LCDI that will not reset cleanly).
• Refrigerant or sealed-system work — seasonal sealing never opens the refrigeration circuit.
• The unit is simply too heavy or awkwardly placed for a safe homeowner removal.

Bottom line

Pull the unit if you can: Frigidaire-style dry upright storage plus a closed, weatherstripped window beats every cover kit for winter heat loss. If you leave it installed — GE and LG both allow that path — unplug, dry it out, foam the side gaps, seal the indoor face completely, and use an exterior cover for weather, not as a substitute for the indoor seal. Covers reduce the problem. They do not erase it.

How I put this guide together

I compared Frigidaire’s winter-storage article, GE’s winterizing/storage page, LG USA’s window-AC winterize article, ENERGY STAR’s room-AC savings tips, DOE Energy Saver’s archived cover-or-store line, and the DOE Building America / NREL homeowner fact sheet on window-AC infiltration. I did not run a lab air-leakage test on my own units for this rewrite. Where brands disagree — Frigidaire leaning to removal, GE calling removal optional, LG documenting cover-in-place — the article states both and lets your model manual break the tie.