Condensation in bathrooms is normal. Persistent condensation that drips, pools on windowsills, fogs the mirror for an hour, or runs down the walls is not. It's a sign that the steam your shower produces isn't being shifted out of the room fast enough, or that it's hitting cold surfaces and condensing instead of being extracted. Here's what actually works to fix it.
Why Bathrooms Condense
Showering for 8 minutes at 40°C produces around 0.2–0.4 litres of water vapour. That vapour is suspended in the warm air of the bathroom. The moment that warm, wet air hits a cooler surface, the vapour condenses back into liquid water — on the mirror, the window, the ceiling corner, the cold external wall.
Two factors decide whether condensation becomes a problem:
- How fast the steam is removed — by extraction. The longer wet air sits in the room, the more it condenses on cool surfaces.
- How cold the surfaces are — by insulation and heating. A wall at 22°C doesn't condense steam; a wall at 14°C does.
You can fix condensation by changing either factor. The fastest results come from fixing both.
Fix 1 — Better Extraction
If the extractor in your bathroom is more than 10 years old, it's almost certainly the biggest cause of your condensation. Old fans lose efficiency through bearing wear, blade fouling, and accumulated dust in the duct. A 20-year-old fan rated at 15 l/s when new is probably moving 6–8 l/s in 2026.
The fix isn't expensive. A modern humidity-sensing extractor (e.g. Vent-Axia Silent, Manrose Showerlite, Envirovent Silent 100) rated at 20–25 l/s, fitted with rigid 100mm duct to an external grille, costs £180–£350 fully installed. Adds maybe a half-day to a bathroom job; can be done as a standalone install too.
Critical specifications:
- Humidity sensor. The fan switches on automatically when humidity rises above ~65% and runs until it drops back. Independent of the light switch.
- Run-on timer. Continues for 15+ minutes after the trigger event ends.
- Rigid duct. Not flexible concertina duct.
- External termination. Through-the-wall to a sheltered grille, not into the loft.
Fix 2 — Warmer Surfaces
Even with perfect extraction, a cold bathroom will condense steam onto its surfaces faster than the fan can clear them. Three changes that warm the room enough to make a real difference:
Insulate cold external walls
The biggest single change in older properties. Solid concrete walls in CDC-era flats and single-skin sandstone in older tenements are the worst offenders. We batten and insulate behind wet wall or tile as standard on every fit in these properties — surface temperature rises by 5–8°C, condensation stops forming on that surface entirely.
Heated towel rail running properly
A heated rail at 50–60°C drives convective air movement through the room — warm air rises off the rail, cold air drops to replace it. The room temperature rises by 2–4°C above ambient and stays there. The trick is running the rail; many homes have one fitted but never bother turning it on except in deep winter.
Underfloor heating on a timer
Most effective for warming the lower portion of the room and the floor itself. Particularly valuable in tile-floored bathrooms where the cold floor is a major condensation point. More on UFH here.
Fix 3 — Shower Habits
Smaller intervention but real. Two things genuinely reduce vapour production at source:
- Shorter showers. Halving the duration halves the vapour generated. Obvious but effective.
- Lower temperature. A 38°C shower produces noticeably less vapour than a 42°C one. Only relevant if you're someone who runs the shower hot.
We mention these for completeness but most customers we work with aren't going to redesign their morning routine. The physical fixes (extraction, insulation, heating) do most of the heavy lifting.
Fix 4 — Demister Mirrors
A demister mirror has a heating pad bonded to the back of the glass. The mirror surface stays just above ambient temperature, so steam doesn't condense on it. Visually, the mirror stays clear during and after a shower while the rest of the room is still steamy.
Worth knowing: the demister fixes the symptom (foggy mirror), not the cause (high humidity). If the rest of the bathroom is condensing steam, the mirror being clear doesn't help — it just lets you see the wet walls more easily. Best treated as a luxury upgrade after the underlying ventilation and heating are fixed.
Standard inclusion on Premium and Luxury bathroom packages. Available as a £120–£200 upgrade on Starter.
When Condensation Is a Serious Problem
Some condensation is normal. The signs that yours is past normal:
- Visible water running down walls or pooling on windowsills after every shower
- Mirror stays fogged for 30+ minutes after the shower ends
- Mould appearing in ceiling corners or external wall surfaces
- Paint or wallpaper bubbling or peeling in the room
- Persistent damp smell even when the room isn't being used
- Visible black spotting on grout joints or silicone within months of cleaning
Any one of these is a sign that the moisture balance is broken and the room needs the underlying causes addressed — not a once-a-month bleach session. Most are fixable for £200–£500 in upgrades; the recurring time and frustration of cleaning costs more than that within a year.
Related reading: bathroom mould — why it keeps coming back, ventilation rules & sizing, why is my bathroom always cold?
Got a condensation problem you'd rather solve than live with? Call 01236 801802 — we can come out, diagnose the actual cause, and quote you for the fix.