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What the side panels actually close
Side panels, which Frigidaire's support page calls side curtains, sit on the sides of the cabinet and close the space between the unit and the window frame. The window sash comes down above the cabinet. Together those parts are what stand between indoor air and outdoor air, and the ENERGY STAR program treats them as a sealing question rather than a cosmetic one.
ENERGY STAR puts a figure on the cost of getting it wrong: a room air conditioner that is installed badly leaks as much air as a hole of 6 square inches, which raises energy use and leaves the room less comfortable. Frigidaire's page makes the same point from the cooling side, saying a unit struggles to hold temperature when new air keeps entering the room, and it lists the side curtains on the unit and the window framing the unit sits into among the openings to close.
So the panels are not a skirt. A loose panel or an open sash gap lets hot outdoor air into the room the unit is trying to cool, and the compressor keeps working against that load. For how much window heat gain matters overall, see why some rooms are harder to cool.
What comes in the box for sealing
The sealing parts ship with the unit, and the makers describe them differently. ENERGY STAR says certified models arrive with better materials and clearer instructions for sealing and insulating around the cabinet, and that their side panels fit tightly so leaks stay small. Its installation advice is to follow the manual and to use the insulation materials included with the unit.
Midea's window air conditioner FAQ describes one specific part: black foam strips whose stated job is to close off the window sash. With the unit in place, the strip sits wedged between the front window and the back window, stopping air from passing through that line. A fuller list of typical contents is in what comes in the box.
Keep the parts together between seasons. Foam strips are easy to misplace, and a missing strip leaves a permanent gap at the window.
Where the foam strip goes
Midea's FAQ describes the strips as closing off the window sash, with the foam wedged between the front window and the back window after the unit is in place, so air cannot pass through.
That location makes sense once you picture the window. Raising the lower sash to fit the unit leaves a gap between the lower sash and the upper sash, and that gap sits above the cabinet, open to the outdoors. The foam strip fills that line between the two windows.
Midea's page describes the purpose, not a sequence of steps. For the exact placement on a given model, the owner's manual that ships with the unit is the document to follow, and the maker's support page is where questions about a specific model go.
The gaps the makers name
The makers' pages name these places on a window install. The table pairs each one with what closes it.
Sealing is about the opening around the unit, not about covering the cabinet itself.
| Leak point | What closes it |
|---|---|
| Gap between the front and back window sash | Foam strip wedged between the two windows, as Midea describes |
| Side curtains or panels | Tight-fitting panels; Frigidaire lists the side curtains among the openings to close |
| Window framing the unit sits into | Insulation materials supplied with the unit, per ENERGY STAR |
| Side louvers on the cabinet | Left uncovered; Frigidaire warns that blocked airflow hurts cooling |
Sealing without covering the side louvers
Frigidaire's page is explicit that the louvers on the sides must not be covered or blocked, since blocked airflow makes the unit struggle to maintain temperature. Midea's FAQ makes a related point when a unit shuts off before the room reaches the set temperature, listing curtains around the unit among the things that impede airflow.
In practice this means foam and insulation belong at the window line and at the frame edges, not across the cabinet's side vents. If a curtain hangs beside the unit, pull it back so it is not pressed against the intake. The seal should close the hole in the wall, not the unit's own air path.
Tilt, drainage and the seal
Midea's page describes a slight backward tilt so that water condensed on the evaporator runs to the rear of the unit and is expelled, and it notes that the outdoor fan uses that water to cool the condenser. ENERGY STAR's installation tips ask for a cabinet that sits level and note that the drainage system depends on it. The two statements pull in different directions, so follow the manual for the specific model, and read why a window AC must tilt toward the outside before changing anything.
Support matters here too, since a cabinet that sags at the back changes its own tilt. L brackets and support brackets explains the hardware that holds a cabinet steady.
Older frames with storm windows raise their own fitting questions. Room ACs and storm windows covers those cases.
Checking the seal through the season
The makers' pages point at airflow as the thing to watch. Frigidaire ties poor cooling to air entering the room through openings, and Midea ties a unit shutting off early to restricted airflow. When cooling slips, the first points to the window line and the openings around the unit, the second to the filter and anything blocking the vents.
At the end of the cooling season, ENERGY STAR suggests taking the unit out where possible to limit heat loss, or covering it with one sized for the unit over the winter. Either way, check the foam strips and panels again before the next season. Taking down and storing a window AC covers the sequence, and getting a room AC ready for the cooling season covers the reverse in spring.
What to look for when buying
Sealing quality is partly a purchase decision. The ENERGY STAR program describes certified units as having side panels that fit tightly, along with better sealing materials, which is one reason the certification is worth checking on the box. What ENERGY STAR means for a room air conditioner explains the criteria, and best ENERGY STAR window air conditioners lists units whose listings state the certification.
For the wider picture on capacity and features, the window AC buying checklist puts the seal alongside sizing and efficiency.
Which to choose
| If you | Look for |
|---|---|
| If the window opening is much wider than the cabinet | Expect to extend both side panels fully to the frame and to use the insulation the maker includes at the edges. |
| If air passes between the two window sashes | Wedge the included foam strip between the front and back window, as Midea describes. |
| If a curtain hangs beside the unit | Keep it clear of the side louvers; Frigidaire warns that blocked airflow makes the unit struggle. |
| If the unit will stay in the window all winter | Plan on a cover sized for the unit, or remove the unit, as ENERGY STAR suggests. |
| If the cabinet rocks when pushed | Look at support brackets before blaming the panels, since a moving cabinet changes its own tilt. |
| If you want the seal sorted at purchase | Look for ENERGY STAR certification, which the program ties to tight-fitting side panels and better sealing materials. |
Questions people ask
Do the sides still need sealing if the panels fit tightly?
ENERGY STAR ties tight-fitting side panels to fewer air leaks, but the window line and the frame edges still need the insulation supplied with the unit. The program compares a badly installed unit to a hole of 6 square inches.
What are the black foam strips that come with a Midea unit for?
Midea's window air conditioner FAQ says the strips are there to close off the window sash. With the unit in place, the foam sits wedged between the front window and the back window, stopping air from passing through.
Can the side louvers be covered to stop drafts?
No. Frigidaire warns that the louvers on the sides must stay uncovered and unblocked, because blocking airflow causes the unit to struggle to maintain temperature. Seal the opening around the cabinet, not the cabinet's own vents.
Should the unit sit level or tilted back?
Midea describes a slight backward tilt so condensed water runs to the back of the unit and is expelled. ENERGY STAR's installation tips ask for a level cabinet and note that drainage depends on it. Follow the manual for the specific model.
Does a better seal make the room colder?
It does not add cooling capacity. What it does is stop outdoor air from entering, which Frigidaire lists as a reason a unit struggles to hold temperature. A sealed opening lets the rated capacity go toward the room instead of the leak.