The best-supported choice for a window air conditioner left installed over winter is a properly sized outdoor window AC cover. Measure the unit’s height, width and depth, then compare all three with the cover’s listed dimensions; a BTU range or “large” label alone cannot confirm fit. An outdoor cover protects the exterior portion from exposure, while an indoor cover or weather seal is a separate option for drafts inside the room.
What makes a good winter cover for a window AC?
Choose an exterior cover that matches the installed unit’s dimensions and has a fastening method that holds it in place. Product descriptions can help you compare material and closure claims, but those claims are not independent performance tests. No independently tested winner or evidence of a particular cover preventing damage, saving energy or extending equipment life is established here.
- Placement: For outdoor weather exposure, choose a cover designed for the exterior of a window AC. An indoor fabric cover does not protect the outdoor portion.
- Fit: Compare the unit’s height, width and depth with the cover’s stated dimensions.
- Material and fastening: Check the manufacturer’s material description and how the cover is secured.
- Indoor drafts: If drafts are the problem, consider a separate interior cover or weather seal rather than treating it as a substitute for an exterior cover.
How listed cover sizes compare
The dimensions below are manufacturer listing specifications, not independent measurements. Product-page publication dates are not stated for Frost King or Randall Manufacturing. Confirm current packaging and actual fit before buying.
| Brand and model | Listed dimensions (inches) | Capacity guidance | Listed material or feature |
|---|---|---|---|
| Frost King AC2H | 18 × 27 × 16 | Up to 10,000 BTU | Heavy-duty reinforced plastic; elasticized fit; exterior covers the bottom of the unit |
| Frost King AC3H | 18 × 27 × 22 | 10,000 to 15,000 BTU | Heavy-duty reinforced plastic; elasticized fit; exterior covers the bottom of the unit |
| Frost King AC5H | 20 × 28 × 30 | 15,000 BTU and up | Heavy-duty reinforced plastic; elasticized fit; exterior covers the bottom of the unit |
| Randall Manufacturing AC-2 | 18 × 27 × 16 | Not stated on product listing | Reinforced polyethylene; elasticized fit |
| Randall Manufacturing AC-5 | 18 × 27 × 22 | Not stated on product listing | Reinforced polyethylene; elasticized fit |
| Randall Manufacturing AC-15 | 20 × 28 × 20 | Not stated on product listing | Reinforced polyethylene; elasticized fit |
Sources: Frost King product listing and Randall Manufacturing product listings. Frost King’s largest listed depth is 30 inches; Randall’s AC-15 listing gives a 20-inch depth. That difference is a practical reason to measure your unit rather than choose by a broad size label or capacity range.
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- 【420D Waterproof Material】: Window air conditioner covers are made of high quality 420D waterproof oxford cloth, with a silver inner layer, better waterproof effect, washable and durable.
- 【Please Choose the Right Size】: Window AC unit cover size is 21W * 16D* 15H inches (53*40*38cm), suit for most of standard window ac units 3,000 - 7,000 BTU.
- 【Double Straps Design】: Outdoor window AC protection cover has two adjustable straps with a snap buckle, making the cover not easy being fall due to wind, and easy to put on and take off.
- 【Isolate Cold Air and Dust】: Black window AC cover not only could protect the ac unit from UV, and dust, but also could keep your room warm in winter, prevent dust, rain, and snow enter to indoors.
- 【Please Note】:Please choose our product according to your air conditioner size. In order to long time use, we suggest cleaning it regularly.
How to prepare and cover the unit for winter
LG USA’s window/through-wall winterization guide, dated May 3, 2023, recommends the following steps. Consult the instructions for your own model, since preparation details can vary.
- Switch the air conditioner off and unplug it.
- Remove debris and clean the evaporator and condenser coils and the filter.
- Let the unit dry completely before covering it.
- Fit a waterproof cover and secure it with vinyl tie-downs, as LG’s guide advises.
- Periodically clear snow, ice and debris from the top of the covered unit.
See LG USA’s winterization guide for the model-specific context.
Rank #2
- 【Three Layers of Insulation for Draft Blocking】Unlike other single-layer AC covers, TOHONFOO's air conditioner covers for outside units features a three-layer structure: 600D waterproof and windproof heavy duty oxford fabric, 2mm thickened pearl cotton, and insulated aluminum foil — Heavy snow? No problem. Dust and debris? Blocked. Your AC unit stays clean, safe, season after season.
- 【Please Choose the Right Size】The inner dimensions of the ac unit covers outdoor are 21"W x 15"H x 16"D, fitting most AC units with outer dimensions of ≤20.5"Wx 14.5"H x 15.5"D . Note: Please measure your unit's width, height, and depth (including any protruding parts) before purchasing to ensure a proper fit
- 【Bottom-cut Design for Bracket Compatibility】No need to disassemble your AC — simply slip the cover on, tighten the straps, and your window air conditioner cover is ready to go. The sewing threads at the bottom form several cuttable sections, so if your unit has a support bracket underneath, you can easily cut the cover to accommodate it
- 【2 x Rust-Proof Metal Buckle & 106.5"Adjustable Strap】Compared to the breakable plastic buckles and flimsy straps used in others, we use durable metal buckles that won't break and reinforced straps that can withstand harsh weather while being easier to install, When the cover is snugly fitted and the straps are securely tightened, it holds strong against winds of 32–38 mph
- 【All Weather Protection】 Our waterproof heavy-duty air conditioner covers for window units are designed to protect your air conditioning unit from harsh weather conditions — rain, snow, wind, and even harsh UV rays (UPF 50+). Built with anti-aging, tear-resistant fabric for lasting durability. Care: wipe with a damp cloth. Do not hand wash or machine wash — gentle wiping preserves the insulation layer
Remove the cover before operating the AC
Take an exterior cover off before running the air conditioner, and follow the unit’s own manual. In a November 5, 2025 support article about outdoor units generally, LG says a cover blocks ventilation during operation and can cause malfunction. That guidance supports the airflow precaution, but it is not a claim that every window AC has identical instructions. See LG USA’s rain-and-snow guidance.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.When an indoor cover or weather seal is useful
An exterior cover and indoor weatherization solve different problems. Frost King lists indoor covers and weather seals; Duck describes its indoor cover as sealing drafts, dust and insects. If cold air is entering the room, consider an indoor draft-sealing accessory separately from the outdoor cover. See Frost King’s cover and seal listings and Duck’s indoor AC cover listing.
Quick Recap
Best Value
- Frost King heavy-duty reinforced 6 mil polyethylene
- Helps protect air conditioning units from damage caused by winter conditions
- Reduces drafts and heat loss
- Comes with an elastic strap for a tight, secure fit
- Window AC cover goes on quickly
Rank #4
- All-Weather Protection: Our heavy-duty outdoor window AC cover is designed to protect your air conditioning unit from harsh weather conditions. It helps to prevent cold air from entering and warm air from escaping the house, ensuring the indoor temperature remains comfortable.
- Triple-Layer Construction: This window air conditioner cover boasts a black waterproof outer layer, an aluminum foil mid-layer for heat reflection, and an insulating pearl cotton inner layer, offering robust protection and energy efficiency in a compact design.
- Adjustable Fit: The outside ac unit cover includes two straps with adjustable metal buckles to secure the fit, offering additional protection against wind and potential damages.
- Customizable Fit for Unique Designs: If your unit has a support bracket underneath, you can easily cut the bottom of outdoor ac cover to accommodate it.
- Perfect Size: With dimensions of 21"width x 15"high x 16"deep, please measure your AC unit before purchasing to ensure the best fit.
Rank #3
- MATERIAL - 1’’ thick insulating foam covered in white flexible vinyl
- FITS WINDOW SIZES- Fits windows 36’’ wide or smaller, panels must be cut to size with scissors
- COVERS THE EXISTING PULL OUT PLASTIC SIDES THAT COME WITH AC - DOES NOT REPLACE THEM
- COMPOSED OF 3 PIECES- 2 side panels with adhesive flaps to connect to AC, 1 long top panel with adhesive flaps that connect to the side panels and AC forming a built-in clean design
- HELD IN PLACE- panels must be cut to fit snuggly in place between window frame and ac, the adhesive flaps attach to the ac only
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
