What "misted" actually means
When a double-glazed pane fogs up, the frame is almost always fine. The sealed unit inside the frame — two panes bonded around a perimeter spacer with butyl and secondary sealant — has lost its seal. Modern UPVC, aluminium and composite frames last 25–40 years; the sealed unit inside lasts 15–20. Once that perimeter seal perishes, moisture works into the cavity and condenses on the inside of the glass — that's the haze. The fix is replacing only the sealed unit, leaving the frame alone.
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Direct-fit unit replacementDrop-in swap, matched to original spacer-bar colour, glass thickness and pattern.
from £100
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Argon-filled upgradeRe-spec with argon gas + warm-edge spacers to cut heat loss.
from £140
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Low-E / Planitherm® glassReflects warmth back into the room, cuts winter heat loss.
from £180
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Toughened & laminatedFor doors and panes within 800mm of the floor (Building Regs Part K).
from £150
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Obscure & patterned glassMatched to existing for bathrooms, en-suites and front doors.
from £120