On this page
- Why the window kit seal decides how well the unit cools
- The foam seals in a Whynter window kit
- Fit the slider to the opening before the foam goes on
- Sealing the sash gap and the panes
- Sliding doors and sliding windows
- Checking the seal with the unit running
- Mistakes that break the seal
- What to check before you buy the unit
- Keeping the seal through the season
- Which to choose
- Questions people ask
Why the window kit seal decides how well the unit cools
A portable air conditioner pulls heat out of the room and pushes it through the exhaust hose, which ends at a window slider kit. The slider fills the open part of the window and the foam strips close what is left. Whynter's troubleshooting guide lists a leaking exhaust among the reasons a unit runs but the room stays warm, and suggests either replacing the hose or wrapping it in insulation when hot air escapes indoors. The same guide says to shut and insulate every window and door to the room while the unit is cooling.
The seal works in both directions. It keeps hot outdoor air from coming in around the plastic slider, and it keeps the unit's own exhaust from curling back into the room. Single-hose vs dual-hose portable ACs explains how that airflow differs between the two designs.
The foam seals in a Whynter window kit
Whynter manuals name the foam pieces by letter. Foam seal A and foam seal B are adhesive strips; foam seal C is non-adhesive. The parts lists in the ARC-102CS, ARC-1030WN, ARC-0850XP and ARC-1280MX manuals all include these three seals, and the number of pieces varies by kit, so check the list for the model in hand.
Midea describes the same job in different terms on its portable air conditioner FAQ: the dense foam strips go above and below the window sliders to create a tight seal, and the less dense foam seals the window sash, the gap between the front and back window.
| Seal | Type | Where the Whynter manuals put it |
|---|---|---|
| Foam seal A | Adhesive | Window sash and frame on a hung window; bottom of the door or window on a sliding installation |
| Foam seal B | Adhesive | Window sash and frame, applied vertically on a sliding window |
| Foam seal C | Non-adhesive | Between the glass and the window frame, or between the two panes |
Fit the slider to the opening before the foam goes on
The slider has to sit in the window opening before any foam is cut, because the foam follows the slider's edges. Whynter's troubleshooting guide covers both misfits. When the opening is shorter than the kit's minimum length, the kit can be trimmed down to the window opening, but the cut-outs for the exhaust or intake hose must stay intact. When the opening is longer than the kit's maximum length, the open space needs extra material, such as Plexiglas, PVC plastic or plywood, or a second slider kit used alongside the included one.
Kit lengths differ by model, so measure rather than assume. The ARC-102CS window kit is listed at 6.5 inches wide and 26.75 inches minimum to 48 inches maximum long. The ARC-1280MX and ARC-1280WX manual describes an adjustable window kit that expands from 28.7 inches to 82 inches. A kit that is too short leaves a gap at one end, and that gap is exactly where outdoor air enters.
Sealing the sash gap and the panes
Foam seal C does the work between the window panes. On a hung window, the Whynter manuals say to trim the non-adhesive strip to the window's width and place it between the glass and the window frame; on a sliding window, trim it to the height instead. The ARC-102CS manual describes the same strip as closing the open gap between the top window sash and the outer window sash. The purpose is to keep outside air, and in the ARC-0850XP manual's wording insects, from entering through the gap where the two sashes meet.
Adhesive strips A and B go on the frame side. The ARC-1280MX and ARC-1280WX manual says to trim the adhesive strips A and B to length and press them onto the window sash and frame. The ARC-0850XP manual adds that on a sliding window the strips are applied vertically. Run them along the full length of the frame rather than dabbing at the corners, since a short strip leaves an unsealed span.
Sliding doors and sliding windows
A sliding installation changes where the adhesive strip goes. The ARC-102CS manual says to trim the adhesive foam seal to length and fix it along the bottom of the door or window, then adjust the window bars and close the door or window on them. The non-adhesive strip still goes between the panes, cut to the height of the opening.
The hose side of a sliding setup has its own rules, and venting a portable AC through a sliding door walks through the parts. Whynter's troubleshooting guide notes that the window screen can stay in the frame while the slider kit goes in, which keeps the job to the slider and the foam.
Checking the seal with the unit running
Run the unit in cool mode and check the window end of the hose. Whynter's troubleshooting guide points to an exhaust hose that is too long, has a sharp bend, or is leaking air as a cause of weak cooling, and asks for the hose to be run as short and as straight as it can be, without extending it beyond 9 feet. Where hot air is escaping into the room, the guide suggests replacing the hose or wrapping it in insulation.
Clearance matters too. The ARC-102CS manual asks for 20 inches of clear space in front of the air intake area, and the ARC-1280MX and ARC-1280WX manual says there should be no obstructions within 20 inches of the air vents. The ARC-1030WN, ARC-1230WN and ARC-1230WNH manual asks for a minimum of 36 inches of clearance around the unit. Curtains and blinds that hang into the exhaust path undo part of the seal's work. How a portable AC gets heat out of the room covers the airflow behind this check.
Mistakes that break the seal
Cutting into the hose cut-outs. Whynter's guide is explicit that the slider can be trimmed for a narrow window but the cut-outs for the exhaust or intake hose must stay intact. A trimmed cut-out will not hold the hose adapter squarely, and the joint becomes a leak.
Leaving the slider loose in a wider window. A slider that stops short of the frame leaves an open strip that no foam strip covers. Whynter's answer is extra material over the open space or a second slider kit, not a longer foam strip.
Skipping the room-side gaps. Whynter's troubleshooting guide also lists open windows and doors to other rooms as a reason a unit runs without cooling the room, and says to shut and insulate them. The window kit is only one part of the envelope.
Skipping the check at reinstall. When the slider goes back in after storage, look over the foam strips and the fit before the hot weather arrives. What comes in the box with a room AC lists the window parts a kit typically includes.
What to check before you buy the unit
The window kit is part of the purchase, so the window opening decides whether a given unit will seal well. Measure the width and height of the opening, note whether the window is hung or sliding, and compare those figures with the kit length the maker lists. Portable AC buying checklist covers the other parts of that decision, and best portable air conditioners ranks units by the Department of Energy figure for portables.
If the room has a wide window or a sliding door, a kit that expands further saves improvising with extra material. If the window is narrow, a kit that can be trimmed without touching the hose cut-outs is the safer choice. Either way, the seal is only as good as the fit between the slider and the frame.
Keeping the seal through the season
Check the foam strips at the start of the cooling season: look for lifted adhesive, crushed sections and gaps at the ends of the slider. Whynter's troubleshooting guide treats a leaking exhaust as a cooling problem, so a quick look at the window end is worth the time.
When the unit comes out of the window, store the slider and any leftover foam with it so the parts stay together. The start of season checklist puts the window kit check alongside the filter and drain checks, which is the order that keeps a portable unit working through the summer.
Which to choose
| If you | Look for |
|---|---|
| If the window opening is narrower than the slider's minimum length | The kit can be cut down to fit, but never cut into the exhaust or intake hose cut-outs |
| If the window is wider than the kit's maximum length | Plan extra material over the open space, such as Plexiglas, PVC plastic or plywood, or a second slider kit used with the included one |
| If the window is a hung window | Adhesive strips on the sash and frame, plus a non-adhesive strip cut to the window width and placed between the panes |
| If the window is a sliding window or door | Adhesive strip along the bottom of the door or window, plus a non-adhesive strip cut to the height of the opening |
| If the room still feels warm near the window | Check the exhaust hose for leaks, sharp bends and length beyond 9 feet, and reseat the foam strips |
| If the window screen is to stay in place | It can stay; Whynter's guide says the screen does not have to come out for the slider kit |
Questions people ask
Does the window screen have to come out to fit the kit?
No. Whynter's troubleshooting guide states that the screen can stay in the frame while the window slider kit is installed. The slider and the foam strips go in with the screen still in place.
What happens when the slider kit is longer than the window opening?
Whynter's guide says the kit can be cut to fit a window opening that is smaller than the minimum length of the slider, as long as the cut stays away from the exhaust or intake hose cut-outs. Measure the opening first and trim only the plain end.
What happens when the window is wider than the kit?
Whynter's guide says additional material is needed to cover the open space, naming Plexiglas, PVC plastic and plywood as examples, or a second window slider kit used in combination with the included one. Foam strips alone will not bridge a wide gap.
Where exactly does the non-adhesive foam strip go?
Between the glass and the window frame, or between the two panes. Whynter manuals say to cut it to the width of a hung window or the height of a sliding window, and the ARC-102CS manual describes it as sealing the gap between the top window sash and the outer window sash.
Why does a portable AC need draining so often?
Whynter's troubleshooting guide points to high ambient humidity and says to shut and insulate windows and doors to the room. For dual-hose models it also suggests taking the intake hose off when the outside air is very humid or it is raining. How a portable AC handles water explains where that water goes.
How much space should the unit have around it?
The ARC-102CS manual asks for 20 inches of clear space in front of the air intake area, and the ARC-1280MX and ARC-1280WX manual says no obstructions within 20 inches of the air vents. The ARC-1030WN, ARC-1230WN and ARC-1230WNH manual asks for a minimum of 36 inches of clearance around the unit.
Does the seal matter in mild weather?
Whynter's guide lists open windows and doors as a cause of a room that will not cool, and says to shut and insulate them while the unit is running. A loose slider works against the unit whatever the outdoor temperature, because the exhaust can return through the same gap.