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Air con window seal for a casement window

Updated: 20 October 2026

The plastic bar in the air-conditioner box is for a sash or a sideways slider. It will not fill the wedge when a UK casement swings out. An air con window seal for a casement window is cloth sized to that hinged gap. Our [air conditioner window seal comparison](/hub/cooling/air-conditioner-window-seal) holds the twelve amazon.co.uk rows and the prices from 19 October 2026. Peter F. used those listings, Appliances Direct's note on the slide bar, and Electrovision's casement sheet. It is not a survey of every uPVC section. A qualifying purchase can earn a commission at no extra cost to you. Outward, inward, and tilt are different fits.

The plastic bar in the air-conditioner box is for a sash or a sideways slider. It will not fill the wedge when a UK casement swings out. An air con window seal for a casement window is cloth sized to that hinged gap.

Our top picks

Derwit Derwit 4 m casement window seal

Best overall

Derwit Derwit 4 m casement window seal
6.7/10about £17.99
View offer
DREO DREO 400 cm window seal

Rank 2

DREO DREO 400 cm window seal
7.3/10about £19.99
View offer
Machine-YA Machine-YA 300 cm window seal

Best value

Machine-YA Machine-YA 300 cm window seal
7.2/10about £16.38
View offer
On this page
  1. 1.Why the box kit misses a casement
  2. 2.Outward, inward, and tilt
  3. 3.Perimeter, locks, and odd frames
  4. 4.What to buy from this set

Why the box kit misses a casement

A slider bar needs two parallel tracks. A casement hinge throws the sash out of that plane, so the bar jams or will not reach. Appliances Direct puts the slide bar on sliding or sash windows. The cloth kits use hook tape on the frame, cloth across the ajar sash, and a zip for the hose. DREO says the 400 cm version fits casements and that sliding windows are not compatible. Derwit says most outward casements. The MOEGFY rows at about £22.89 and about £29.99 say tilt and casement, and not sliding. Machine-YA says side-hung, bottom-hung, and skylights, and not a sliding door. LYUNIT and VOLIKRA do not name the window. Silence is not permission.

Outward, inward, and tilt

Outward-opening uPVC is what many UK kits mean by casement. The gap can be wider at the handle than at the hinge. Derwit's reviews say it fitted casements people were unsure about. A shared MOEGFY review says outward was harder than inward. A VOLIKRA reviewer says a pictured standard casement did not match an inward window. Bottom-hung and top-hinged windows are named on Machine-YA, EGNBU, and in the OWYR reviews. Fit the cloth for the handle position you will leave while the unit runs. A tilt-and-turn window is not one bullet in this set. One DREO reviewer had to refit a Velux kit to open the roof window.
Derwit Derwit 4 m casement window seal

Testsieger

Derwit Derwit 4 m casement window seal
6.7/10about £17.99
View offer

Perimeter, locks, and odd frames

Measure the top and the two uprights, and skip the hinge. Electrovision's fabric kit stops at a 4 m perimeter. Three sides of 90 cm and 110 cm and 110 cm add to 310 cm and miss a 300 cm listing. That sum is an example. The length split is in the buying guide. Derwit reviewers worked around security locks, and one said the tape does not reach some bottom-hung windows. Run the tape in sections past the keep. An OWYR reviewer said the fabric was too narrow for a recess, and a cantilever uPVC window would not take the cloth. Keeping tape off the glass is on the how to fit page.

What to buy from this set

The top pick is the DREO 400 cm at about £19.99, 4.2 from 85 reviews: casement stated, sliding excluded. The 4 m × 4 m size line clashes with a 400 cm strip. Derwit at about £17.99, 4.4 from 32, is aimed at most outward casements, and the hook tape is not strong on every frame. Machine-YA at about £16.38 is the best value under 300 cm. The MOEGFY tilt-and-casement lines share one 4.0 from 4,220 pool. Skip LYUNIT if the listing must name a casement, and skip OWYR at about £25.99 on a cantilever frame. A cut panel is the fabric versus rigid panel fork. A sash is the wrong family for this cloth.

Common questions

Will a universal kit fit an outward-opening uPVC casement?
It will if the listing actually covers an outward casement and the three sides you measure are within the length. Derwit says most outward casements. DREO says casement and not sliding. A title that only says universal, with no window sentence, has not made that promise. One shared MOEGFY review still found outward harder than inward.
What about a tilt-and-turn or a top-hung window?
Fit the cloth for the position you will leave the handle in. Machine-YA and EGNBU name bottom-hung windows and skylights. OWYR reviews mention British top-hinged windows. A tilt-and-turn window is not covered by a single bullet in this set, so check that the sash can sit ajar without the cloth binding the hinge. A Velux fit in the DREO reviews had to be removed to open the window.
Do window locks stop the tape?
They interrupt it. Derwit reviewers worked around security locks on the frame, and one found the tape short on a bottom-hung window. Run the tape in sections past the keep, on a clean, dry frame. Do not bridge a bolt with a stretched strip and expect it to hold once the hose pulls.
Is a sash window a casement?
No. A sash slides vertically in runners. A casement is hinged. The bar in the air-conditioner box is the sash tool. The fabric kits that mention sliders tell you not to use them there. Do not tape a zip cloth into a sash and then try to shut it.
How do you measure a casement for 300 cm or 400 cm?
Add the sides the cloth covers, usually the top and the two uprights, and skip the hinge. Compare the total with 300 cm or 400 cm. A 90 cm by 110 cm example is 310 cm and needs the longer cloth. Electrovision's own fabric kit stops at a 4 m casement perimeter. Measure yours rather than copying a diagram that draws four sides.
What if the frame is cantilever-shaped?
Treat a cantilever uPVC section as a likely miss for these cloth kits. One OWYR reviewer said the kit would not fit that shape, and another said the fabric was too narrow for a recess. A flat outward casement is the case the Derwit and DREO bullets describe. A shaped bay is closer to a made-to-measure panel than to a 400 cm strip.

Related pages

Best window seal

Air conditioner window seal

Choosing a portable air conditioner window seal kit

Fabric window seal vs acrylic panel for portable AC

How to fit an air conditioner window seal properly

Sources

Public UK sources from the research digest, used for this page on 20 October 2026. Prices, stars, and review counts are the amazon.co.uk figures in the 19 October 2026 snapshot. NHS and GOV.UK pages do not recommend these kits.

  1. NHS: heatwave, how to cope in hot weather (retrieved 19 October 2026)
  2. GOV.UK: beat the heat, keep cool at home (retrieved 19 October 2026)
  3. Consumer Rights Act 2015, section 9 (retrieved 19 October 2026)
  4. GOV.UK: product safety advice for businesses (retrieved 19 October 2026)
  5. GOV.UK: reporting product safety issues (retrieved 19 October 2026)
  6. Aircon Revolution: window seal kits for portable air conditioners (retrieved 19 October 2026)
  7. Ideal Home: portable air conditioner window kits (retrieved 19 October 2026)
  8. Appliances Direct: how to install home air conditioning (retrieved 19 October 2026)