Quick Answer: If you’re leaving your window AC in place over winter instead of removing it, cover both sides. Outside, a waterproof wrap like the Sturdy Covers AC Defender (~$33-40, 600D oxford fabric) keeps rain, snow, and ice out of the housing. Inside, a quilted insulated cover like the Jeacent Indoor Air Conditioner Cover blocks the cold draft that otherwise leaks straight through the unit’s accordion panels and vents. Most manufacturers still recommend fully removing a window unit for winter — a cover is the realistic fallback for anyone who can’t.
Manufacturer instructions all say the same thing: pull the unit out for winter. In practice, a lot of window AC owners — especially renters and anyone dealing with a heavy 80-100+ lb unit — leave it in the frame instead. A cover doesn’t make that as good as removing the unit, but it’s the difference between an exposed compressor and a sealed one, and between a drafty window and a weatherstripped one.
Why a cover matters more than it looks
| Metric | Figure | Source |
|---|---|---|
| Share of home heat loss attributed to windows | ~30% | U.S. Department of Energy |
| Potential energy savings from sealing home air leaks (incl. weatherization) | Up to 30% | U.S. Department of Energy |
| Share of heating/cooling energy lost to air leakage generally | 25-40% | ENERGY STAR |
| Typical outdoor vinyl cover price | ~$25-40 | Amazon/eBay retail listings |
A window AC left in the frame all winter is, functionally, a second leaky window inside your window — the same accordion side panels and vent flaps that let cool air escape in summer let cold air and drafts in during winter. The DOE puts windows at roughly 30% of a typical home’s heat loss, and a window unit sitting unsealed in the middle of one only adds to that. It’s the same air-leakage math behind our installation kit guide, just running in reverse: instead of sealing gaps during a summer install, a winter cover seals the same gaps to keep the cold out.
Our top picks at a glance
| Cover | Best for | Type | Price |
|---|---|---|---|
| Sturdy Covers AC Defender | Best overall outdoor | Waterproof 600D oxford | ~$33-40 |
| Jeacent Indoor AC Cover | Best indoor/draft-blocking | Quilted poly/cotton, double insulation | ~$15-25 |
| TOHONFOO 3-Layer Cover | Best budget outdoor | Waterproof 3-layer, triple insulation | ~$20-30 |
| BJADE'S Foam Side Panel Kit | Best for gap-only sealing | Insulating foam side panels | ~$15-20 |
1. Sturdy Covers AC Defender — Best Overall Outdoor
Sturdy Covers AC Defender
- Waterproof 600D oxford fabric shell built specifically to wrap the exterior-facing housing of a window unit, keeping rain, snow, and ice out of the compressor and coils.
- Comes in "winter" and "all-season" versions — the all-season option adds mesh venting so the cover can stay on even if you run the unit on mild days.
- Elastic and drawstring closures keep it snug against wind rather than flapping loose, which matters most on upper-floor installs exposed to more wind.
The AC Defender is built for exactly one job — keeping weather off the part of a window unit that sticks outside the frame — and it does it with a heavier fabric and better seam sealing than the generic covers that show up first in a general search. If your unit is staying in the window through winter, this is the piece that protects the hardware itself; pair it with an indoor cover below for the draft side of the problem.
2. Jeacent Indoor Air Conditioner Cover — Best Indoor/Draft-Blocking
Jeacent Indoor Air Conditioner Cover
- Quilted poly/cotton outer layer with a wind-blocking poly lining underneath — double insulation designed specifically to stop cold drafts, not just dust.
- Installs from inside the room with elastic straps in one step, no tools, and comes off just as fast if you need the unit running on a warm winter day.
- Sold in four sizes (XS through Large), so measure your unit's interior-facing dimensions rather than guessing from BTU.
Don’t sweat the heat wave — Prime delivers a cover or a whole new AC to your door in two days, and you can try it free for 30 days.
This is the cover that actually addresses the DOE’s 30%-of-heat-loss stat above — an outdoor shell keeps weather off the unit, but it does nothing about the draft leaking through the unit’s vents and accordion panels into your room. The Jeacent’s quilted double-insulation layer sits right over that gap from the inside, which is the same reason our installation kit picks lean on foam weatherstrip for the sash gaps in summer.
3. TOHONFOO 3-Layer Cover — Best Budget Outdoor
TOHONFOO 3-Layer Window AC Cover
- Waterproof outer layer over a triple-layer insulated build, with metal buckles for a more secure fit than basic elastic-only covers.
- Priced below the AC Defender while covering the same core job — keeping rain and snow off a unit left in the window.
- A reasonable step-down pick if you don't need the AC Defender's heavier fabric and just want basic weather protection.
If the AC Defender is more cover than your budget or your climate calls for, the TOHONFOO covers the same waterproof-shell job at a lower price point. It won’t hold up to a harsh multi-winter freeze-thaw cycle quite as well as a heavier 600D fabric, but for most climates it’s enough.
4. BJADE’S Foam Side Panel Kit — Best for Gap-Only Sealing
BJADE'S Window AC Side Insulated Foam Panel
- One-piece foam surround panel that seals the side gaps and accordion panel area specifically, rather than wrapping the whole unit.
- A narrower fix than a full indoor or outdoor cover — worth it if your unit's housing is already sealed tight and the gaps are the only leak point.
- Overlaps in job with the foam side panels in our installation kit guide, which covers the same gap-sealing job for a summer install rather than winter storage.
How to choose
- Leave it in or take it out? A cover is the fallback for units that stay in the window, not an equal substitute for removal — every major manufacturer’s manual still recommends pulling the unit for winter if you can.
- Outdoor cover protects hardware, indoor cover stops drafts. They solve different problems and most owners leaving a unit in place all winter are best served by both, not one or the other.
- Measure before you buy. Covers are sized to a unit’s exterior or interior dimensions, not its BTU rating — check your unit’s width, height, and depth against the listed size range.
- Don’t cover a running unit. A sealed weatherproof cover traps heat and moisture around a compressor that’s actively running — only cover the unit once it’s powered off for the season, or use a mesh “all-season” version if you need airflow on mild days.
Already have the unit installed and just need the gap seal for the season it’s running? Our installation kit picks cover the accordion side panels and foam weatherstrip for that job, and our bracket picks cover the support hardware underneath. If the unit’s been drafty or leaking even with a cover on, check our window AC leaking water guide for the tilt and seal issues a cover alone won’t fix.
The bottom line
If you’re leaving your window AC in place through winter, cover both sides: the Sturdy Covers AC Defender outside to keep weather off the housing, and the Jeacent Indoor Air Conditioner Cover inside to stop the draft. Budget-conscious shoppers can step down to the TOHONFOO for outdoor protection, and if your unit’s housing is already sealed and only the side gaps leak, the BJADE’S foam panel kit handles that narrower job on its own.