A smaller replacement fan can leave a bigger mess than customers expect. On a recent electrical job in Belgravia, our team removed a large faulty bathroom extractor fan. The new humidity-controlled fan had a smaller body, so the old ceiling cut-out could not simply take the replacement.
If you ignore that gap, you get an ugly finish and a weak fixing. Steam can also creep into the ceiling void. In a bathroom, that can lead to staining, mould, loose plaster and hidden damp around the opening.
Kensington Maintenance Services Ltd dealt with the electrical replacement and the ceiling repair together. We protected the bathroom with dust sheets, removed the faulty fan, repaired the ceiling with plasterboard, plaster and reinforced fibre mesh, then installed the smaller fan beside the made-good area. We left the ceiling ready for painting.
Why Oversized Extractor Fan Openings Need Proper Repair
Bathroom extractor fans do not all share the same footprint. Older or heavy-duty units often need a larger ceiling cut-out. Many Belgravia flats and townhouses also have altered bathrooms, boxed-in ducts and previous ventilation work from different refurbishments.
A smaller fan cannot cover a large hole safely on its own. The screws need solid material behind them. The fan body also needs the right support, clean duct connection and safe electrical termination.
Bathrooms add another layer of risk. Steam finds gaps quickly, especially in flats with limited natural ventilation. Any electrical work in a bathroom also needs proper care under BS 7671 wiring rules and Part P of the Building Regulations where applicable. Use a competent electrician, and ask for a professional inspection when you feel unsure about zones, wiring or fan controls.
Isolate the Supply and Check the Existing Fan
Start with safe isolation before touching the fan. Our electrician isolated the circuit and checked the fan wiring before removal. Bathroom fans can connect to a local isolator, the lighting circuit or a timer feed, so guessing can create danger.
We then inspected the existing unit and the surrounding ceiling. The old fan had failed and needed removal. The key issue came from the size difference between the old unit and the smaller replacement.
Cover the Bathroom Before Any Cutting or Plaster Work
Ceiling repairs create fine dust. We fully covered the bathroom areas with dust sheets before we started. That protected sanitaryware, tiles, fittings and the floor.
This step matters in finished bathrooms. Plaster dust can mark taps, sit in grout lines and scratch polished surfaces during clean-up. A few extra minutes of protection saves a lot of cleaning later.
Remove the Large Faulty Extractor Fan Cleanly
We removed the old fan without tearing more of the ceiling than necessary. Large ceiling-mounted fans often leave rough edges around the cut-out. Pulling them out quickly can damage plasterboard around the opening.
After removal, we checked the duct route and the available wiring for the new humidity-controlled fan. Many humidistat fans need a permanent live and neutral. Some models also accept a switched live, depending on how the customer wants control.
Repair the Ceiling Opening With Plasterboard and Fibre Mesh
The replacement fan did not fill the old hole, so we made good the ceiling first. We fitted plasterboard to close the oversized opening. That gave the repair a proper backing instead of a thin skim over a void.
Next, we used reinforced fibre mesh across the joint area. Mesh helps reduce cracking where new repair work meets the existing ceiling. Bathrooms move slightly with heat and humidity, so reinforcement makes sense around old fan openings.
We then applied plaster and worked the surface flush. The brief here required a ceiling ready for painting, not a full decorative finish. Fresh plaster needs drying time before paint, and the first coat should usually be a mist coat.
Fit the Smaller Fan Next to the Repaired Area
Once the repair area had its structure, we installed the smaller fan beside it. That avoided fixing the fan into weak patched edges. It also allowed a neater finish around the new fan body.
Good placement matters. The fan needs to pull steam from the shower or bath area effectively, while still respecting bathroom electrical zones and the manufacturer’s instructions. The duct run also needs a clear route, without crushed flexible ducting or loose joints.
Set the Fan to Run on Humidity Detection
The customer wanted the fan to run automatically on humidity detection. That removes the need to switch it on and off manually every time. It also helps in rental properties, guest bathrooms and busy family homes.
We set the fan controls so the unit reacts when moisture rises. A humidistat setting needs balance. Set it too low and the fan runs too often. Set it too high and the bathroom stays damp for too long.
After setup, we checked the operation. The fan needed to start from humidity demand rather than relying only on manual switching. That final test matters just as much as the physical installation.
Clean Down and Leave the Ceiling Ready for Painting
Once we completed the electrical work and ceiling repair, we removed the dust sheets carefully. We cleaned the surface areas so the bathroom looked tidy again. Nobody wants plaster dust left around a basin or bath after a maintenance visit.
The repaired ceiling area then only needed drying and painting. We always tell customers not to rush paint on new plaster. If you trap moisture under paint, the finish can peel or flash.
Practical Costs, Timing and Checks Before You Book This Work
For similar electrical work, our electrical rate is £90 per hour plus VAT, which is £108 including VAT at 20%. If the job needs handyman making-good work, our handyman rate is £80 per hour plus VAT, which is £96 including VAT. Larger plastering or decorating packages can need an individual quote, in line with standard London rates.
A simple like-for-like bathroom extractor fan swap in London often costs around £180 to £350 for labour, plus the fan, when the wiring, duct and hole all suit the new unit. A job like this Belgravia one costs more because it includes removal of a larger fan, ceiling repair, fibre mesh reinforcement, plastering and humidity-control setup.
Fan choice also affects the final cost. Basic bathroom fans cost less than good-quality humidistat models. You also need to consider noise level, extraction rate, duct length and IP rating for the bathroom location.
Before you buy a fan, check the size of the existing opening. Measure the visible grille and look at the manufacturer’s dimensions if you can access them safely. Do not remove a live bathroom fan just to check the cut-out.
Landlords should think about ongoing use. A humidity-controlled fan often gives better protection than a manual fan, because tenants may forget to switch a standard unit on. For rented homes, keep records for electrical work and arrange inspections where safety or compliance needs checking.
Frequently Asked Questions
Q1: Can I replace a large bathroom extractor fan with a smaller one?
Yes, but you usually need to repair the old ceiling opening properly. A smaller fan needs a solid fixing and a neat, sealed finish around it.
Q2: Does bathroom extractor fan installation need an electrician?
Use a competent electrician for bathroom fan wiring. Bathroom electrical work must follow BS 7671, and Part P rules may apply depending on the work.
Q3: How much does this type of extractor fan job cost?
Our electrical rate is £90 per hour plus VAT, which is £108 including VAT. Ceiling repair or handyman work may add time, and we quote after checking the fan, wiring and making-good required.
Q4: Why choose a humidity-controlled extractor fan?
A humidistat fan runs when moisture rises, so it does not rely on someone remembering the switch. That helps reduce condensation and mould risk.
Q5: Can you leave the repaired ceiling ready for painting?
Yes. On this Belgravia job, we repaired the ceiling with plasterboard, plaster and reinforced fibre mesh, then left it ready for painting after drying.
The main lesson from this Belgravia extractor fan installation is simple: do not treat a smaller replacement fan as a quick swap when the old ceiling opening is too large. Repair the ceiling properly, fit the fan into sound material, and set the humidity control so it actually protects the bathroom. If you have a faulty bathroom fan, an oversized cut-out or a fan that needs automatic humidity detection, our electricians and maintenance team at Kensington Maintenance Services Ltd can help. Send us the details through our contact page and we will advise on the cleanest, safest way to get it done.