The Tool Desk
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The best way to seal a window air conditioner is to install it as its manufacturer directs, use the supplied gasket and weatherstripping, then seal any remaining gaps with material suited to their location. Check the sill, movable sash, side panels and the joint between the window sashes—not just the top of the unit. Keep drainage, ventilation, controls and safe window operation clear.
Where to check for air leaks
With the AC installed, inspect each point where air can pass between the unit and the window opening. ENERGY STAR’s room air conditioner guidance and its program materials identify several interfaces to check:
- Sill and lower edge: Look where the unit rests against the sill.
- Movable sash: Check the contact line where the lowered sash meets the top of the unit.
- Side curtains: Inspect where each curtain meets the window frame and the AC cabinet. A missing, damaged or undersized curtain may leave a larger opening than weatherstripping can address.
- Between the window sashes: Check the gap between the fixed and movable sections of the window.
- Other unit-to-frame joints: Look for gaps around the edges of the installation, following the mounting arrangement shown in the AC manual.
ENERGY STAR says an improperly installed room AC leaks as much air as a 6-square-inch hole. That comparison describes leakage from an improper installation; it does not quantify the savings from any particular repair.
How to seal the gaps
- Read the AC’s installation instructions. Identify the intended mounting position and sealing locations for your model and window type. Start with the gasket and insulation materials supplied with the unit; ENERGY STAR advises using the included materials and following the instructions.
- Install and secure the unit as specified. Confirm the side curtains are extended and fitted as intended. If a curtain is missing, damaged or does not span the opening, check for a replacement or supplemental panel compatible with your AC and window before trying to fill the entire opening with tape or foam.
- Measure each remaining gap. Note its location and width so you can choose a seal that fills it without interfering with the sash, unit or controls. Do not assume one material or thickness will suit every gap.
- Fit a compatible weather seal or gasket. Small gaps at a sash or contact point may be suited to compressible weatherstripping. ENERGY STAR’s draft Version 4.1 specification gives vinyl-clad foam, EPDM cellular rubber and silicone rubber as examples of materials intended to limit air leakage and resist water infiltration and UV degradation. This is material guidance, not a universal product prescription or a claim that the draft is a binding requirement.
- Check the installation’s operation. Make sure the unit remains level as its instructions require, drainage works as designed, vents and controls are unobstructed, and the window can still be operated or secured safely.
Choose a seal based on the gap
| Where the gap is | What to consider |
|---|---|
| Small gap at a sash or contact point | Measure first and consider compressible weatherstripping or a gasket compatible with the window and AC instructions. |
| Opening at a side curtain | Check whether the curtain is correctly extended and fitted. For a damaged or undersized curtain, look for a replacement or supplemental panel sized for the specific unit and window. |
| Exposed seal subject to weather or sunlight | Choose a compatible material suited to that exposure. ENERGY STAR’s draft Version 4.1 specification lists vinyl-clad foam, EPDM cellular rubber and silicone rubber as examples. |
| AC removed for the season | Where possible, remove the unit at the end of the cooling season. If it remains installed, ENERGY STAR recommends an appropriately sized cover; this is separate from sealing an AC that is in use. |
What not to block or assume
- Do not cover the AC’s vents, controls or drainage paths, or interfere with any clearances specified by the manufacturer.
- Do not seal the window in a way that prevents safe operation or securing of the sash.
- Do not treat household caulk as a substitute for the unit’s intended, removable installation seal. Follow the AC and window instructions for the materials and mounting arrangement.
- Do not expect a particular percentage reduction in energy use or bills from sealing one window AC. The cited official guidance does not quantify savings from this specific repair.
ENERGY STAR separately reports an EPA estimate of average savings of 15% on heating and cooling costs, or 11% on total energy costs, for home air sealing plus insulation in areas such as attics, floors over crawl spaces and basements. Those figures concern broader home improvements, not sealing a window AC alone; see ENERGY STAR’s explanation of sealing and insulation.
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Quick Recap
Bestseller No. 1
Bestseller No. 2
Bestseller No. 5
Best Value
ECOHomes Window Weather Sealing Tape (2 Inch Wide x 90 Ft, Clear)
- WINDOW AND AIR CONDITIONER SEALING TAPE: Stop drafts and energy loss instantly with a tape designed to seal gaps around windows, doors, and AC units. Whether you are filling spaces around a window air conditioner or sealing a drafty frame, this tape keeps your home comfortable in every season.
- DESIGNED FOR ALL WINDOW TYPES: This versatile weather seal keeps your home cozy in the winter and cool in the summer. It is the practical choice for sliding windows, casement frames, and AC units, providing a reliable barrier against heat, cold, and humidity throughout the year.
- STRONG HOLD THAT STAYS SECURELY IN PLACE: Our high-performance sealing tape features a strong adhesive that grips firmly and does not peel off on its own. It blocks moisture, dust, and outside noise more effectively than ordinary weather stripping, ensuring your home remains quiet and well-insulated all season long.
- GENTLE ON SURFACES, RESIDUE-FREE REMOVAL: You can protect your home without worrying about your paint. This weather-proof tape is gentle on wood, glass, and vinyl frames, allowing for a clean, residue-free removal when the season changes. No scraping or sticky mess left behind.
- SIMPLE TOOL-FREE APPLICATION: Just cut or trim the tape to your desired length and press it firmly into place by hand. It is a fast, tidy solution for any sealing task. Choose our standard 2 or 3-inch widths for typical frames, the 4-inch wider width for larger gaps, or the 6-inch extra wide width for heavy-duty AC unit insulation.
Rank #4
Window Sealing Tape, Window AC Sealing Around Vents,Insulation,3 Inch Wide
- [WEATHER SEALING TAPE]: Yinttian window weatherproof sealing tape can prevents airflow,rain,smoke,dust and cold air or heat air from entering through window gaps. Waterproof,moisture-proof, and impermeable,it is suitable for all seasons,preventing cold winds as low as -20°C from penetrating your home, even in extreme cold
- [RESIDUE FREE]: Yinttian thickened Insulation tape offers strong stickiness and adhesion, provides a long lasting sealing, can be pasted firmly on the window for the whole winter or summer, and will not damage the surface when it is remove
- [Improve your home energy efficiency and reduce heating/cooling costs]: Yinttian Insulation Weather Stripping can block the gaps around your window air conditioner; easy to use, please ensure that the surface is dry and dust-free before application
- [WIDELY SEALED]: Yinttian reinforced window tape can be cut and designed freely, suitable for sealing gaps and cracks of various sizes on windows, doors, kitchen cabinets, bathrooms, basements, etc.
- [3 inch x 65.5 feet]: Wide window Insulation tape
Rank #3
Sale
Window Air Conditioner Insulated Foam Side Panels Block Hot/Cold Air
- ✅ Superior Insulation Performance to Cut Energy Bills: Our window AC insulated foam side panels are made of high-density, closed-cell foam that effectively blocks outdoor hot/cold air from seeping into your room. By forming a tight seal around your window AC unit, they prevent cool air loss in summer and warm air escape in winter, helping you reduce up to 30% of your monthly energy costs. Say goodbye to wasted electricity and uncomfortable temperature fluctuations!
- ✅ Universal Fit for Most Window AC Units: Designed to fit most standard window air conditioners with BTU ratings from 5000 to 22000 (a common range for residential use), these foam insulation panels can be easily trimmed with a utility knife to match your specific window size. Each pack includes 2 panels, covering both sides of your AC unit, and fits window widths within 17 inches. No need to worry about mismatched sizes，customization is quick and hassle-free!
- ✅ Weatherproof & Durable for Long-Term Use: Unlike flimsy plastic or thin foam alternatives, our AC side insulation panels are built with weather-resistant materials that withstand rain, wind, UV rays, and extreme temperatures (from -20°F to 120°F). The outer layer is dust-proof and easy to clean, while the inner foam retains its shape and insulation properties for years. Protect your AC unit and maintain consistent insulation performance season after season.
- ✅ Reduce Noise & Improve Comfort: The dense foam structure of these panels not only insulates temperature but also absorbs outdoor noise (such as traffic, wind, or neighbors’ sounds) and minimizes AC unit vibration noise. Create a quieter, more peaceful indoor environment, perfect for bedrooms, living rooms, home offices, or nurseries. Enjoy cool air without the constant hum of your AC or distractions from outside!
- ✅ Tool-Free, 5-Minute Easy Installation: No drilling, no screws, no complicated tools required! The package comes with one roll strong, reusable double sided tape that stick firmly to the sides of your window AC unit and the window frame. Simply measure your window gap, trim the foam to size (if needed), peel off the adhesive tape on the panels, and press the panel into place. Installation is so simple that anyone can do it—no DIY experience necessary. Plus, the side panels are easy to remove and reattach when you need to clean or store your AC unit.
Rank #2
MD Building Air Conditioner Weatherseal for Window Units, Gray, 42in
- SNUG INSULATING FIT – Designed as a foam window seal and window foam seal strip to create a tight barrier around window AC units. This air conditioner window seal helps reduce drafts and improve overall foam window insulation.
- YEAR-ROUND CLIMATE CONTROL – Seals out cold air in winter and hot air in summer using high-performance weather stripping foam. Ideal as AC insulation foam and air conditioner insulation for improved indoor comfort.
- PERFECT SIZE FOR SMALL GAPS – Measures 42 in. L x 1-1/4 in. W x 1-1/4 in. H and seals gaps up to 1-1/4 in. thick. Functions as a window insulation strip or insulation strips for gaps around window units.
- DURABLE GRAY FOAM DESIGN – Gray foam strip blends with most window frames while acting as a reliable foam seal and weather seal for windows. Strong insulating foam structure helps block outside air and dust.
- ENERGY SAVING DRAFT STOPPER – Works as a draft stopper for air conditioner units and window gap filler. This foam weather stripping enhances energy efficiency and supports better window AC insulation performance.
#1 Best Overall
Breeze Stop Surround Insulation Side Panels White for Window AC Unit Indoor Air Conditioner Cover for Winter and Summer
- 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
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