This article will explain why you need to think about heating and ventilation when renovating an existing bathroom if you are to avoid odours, condensation and damp.


Excess moisture in bathrooms can lead to dampness, condensation and black mould growth.

Telltale signs of excess moisture are:

  • Mould growth
  • Damp areas on walls – often in upper corners
  • Peeling wallpaper
  • Deteriorating plaster or paint
  • Mildew
  • Condensation on windows, wall tiles and mirrors

If you are renewing your bathroom, it is a great time to take action to prevent the problems associated with excess moisture.


There are 4 theoretical ways to prevent condensation associated with bathrooms:

  • Increase the temperature of the bathroom.
  • Extract the moist air.
  • Reduce the amount of moisture being created through design.
  • Use specialist anti-mould products.

1. Heating & Insulation

Making the bathroom warm will not only result in a more pleasant bathing environment, but will help to keep damp & condensation at bay. This is because warm rooms are capable of carrying more moisture in the air, and warm rooms have less cold surfaces onto which water vapour can condense.

Keep the heat in

When installing a new bathroom (if applicable) consider replacing old windows with double glazed units. This will ensure that the internal glass panels in your bathroom are considerably warmer and less likely to have water condense on them, and will also help to retain heat within the room. Trickle vents can be included on new windows, allowing moist air to escape to the outside (even when the window is shut).

If ‘boarding out’ the bathroom when starting from ‘back to brick’, it would be wise to use thermally efficient tile backer boards instead of standard plasterboard to reduce the amount of heat being lost through the external walls. This is particularly important if your house has solid walls in exposed locations. Please see my article on preparing walls for tiling and tile backer boards for more information on this topic.

Ensure your loft (normally above your bathroom) is fully insulated to recommended levels. Check for local council schemes run in conjunction with energy companies to see if you can get this done for free.

Also, check whether you are entitled to free cavity wall insulation on the same schemes:

Add more heat

When replacing an existing radiator with a towel warmer, be aware of the difference in heat output (measured in BTU’s) as some modern chrome ladder-type towel warmers do not produce as much heat as a comparably sized tradition convector radiators.

In some instances, it is better to add a towel warmer to a new radiator rather than merely replacing it, as you may otherwise have a colder bathroom come winter time.

Radiators should be located on the coldest wall if possible – usually an external wall to aid convection.

Consider installing underfloor heating if your budget allows.

2. Ventilation (extraction)

Extractor fans

Extracting moist air and bathroom smells can be achieved with the use of an extractor fan, which essentially suck out moist air through a hole in the external wall of your bathroom via a fan.

When installing a new bathroom, building regulations state that you don not have to fit a bath fan if there aren’t any currently, but I would recommend doing it anyway.

They are normally wired into the existing lighting circuit so that when the light is turned on, the fan turns on, and when the light is turned off the fan is turned off.

The fan can also normally be isolated by a separate pull cord inside the bathroom or a switch mounted outside the bathroom (often above the door). This ensures that you don’t have to listen to a noisy fan (in an en-suite for instance) when your partner uses the toilet in the middle of the night.

PS All fans usually have a Db (noise) rating so if your are looking for a quiet bathroom fan, bear this figure in mind.

Venting out through the roof

If there are no external walls in you bathroom, you can fit a fan in the ceiling that takes moist air out through the roof, though this can be a bit more complicated.If the duct passes through an unheated roof void the duct should be insulated to reduce the formation of condensation. A vertical duct should also be installed with a suitable weatherproof roof cowl. A condensation trap must be fitted in order to release the condensation build up.A shower enclosure, or a shower in a confined space such as a basement will require an in line extractor which can extract the moist air over a longer distance.Always use an In line Duct or Safety Extra Low Voltage (SELV) fan to ventilate a shower cubicle (zone 1).

Top tip

Never vent moist air into your loft space!Moist air will condense on the timbers and could run down them, possibly causing damp stains to appear on your bedroom ceilings.Also, shut the door when the fan is running for maximum efficiency.

Variable options are available:

Timed extractor fans work as stated above but stay turned on for a pre-determined period of time after the light has been turned off to expel any excess moist air or odours.

Humidity sensor extractor fans operate in the same way but also have an inbuilt humidity sensor which turns the fan on whenever moist air is detected (independently of the light) The optimum humidity level is pre-determined when installing the unit (and a bit of trial and error is often required to get this setting right.)


The best place to site a fan is opposite the bathroom door on an external wall, as high as possible.

This will ensure maximum airflow of fresh air throughout the whole room.

Size of fan

Most 4” fans extract around 90m3 / hour and are by far the most commonly used in bathrooms.

Larger, 6” fans extract over 200m3 / hour and are used when manual ventilation is limited (no windows for example), or the space is very large, or has had damp or condensation problems in the past.

Best bathroom fan

In my own bathroom, and in several customers bathrooms in Leeds I have fitted the following:

Airflow Icon 15/30 Extractor fan

This fan has a shutter that opens when the fan is turned on.

As well as looking great, this means that cold air is prevented from being blown back into the bathroom from outside, when fitted with a louvre vent as shown.

Louvre vent

Using this type of extractor fan allows me to prevent fitting a flapped vent which I don’t like.This is because the flaps often bounce when it’s windy outside (or when the fan is operating) making a very annoying noise and ruining a relaxing bath. If you are looking for a quiet bathroom fan, you should bear this in mind as well.

Soil pipe used as ducting

This option is more durable than using flexible ducting secured with jubilee clips, and leaves less gaps for rodents in the cavity wall to exploit. It is also normally on hand, and I use expanding foam and cement to fix it in place.This should be slightly angled away from the fan to prevent condensation from flowing back into the fan.

3. Design

Number 3 is not really a major consideration unless all other areas have failed to deal with the problem, so will not be covered here. Things that could be considered may be swopping a shower for a bath to produce less airborne moisture.

4. Anti-mould products

Mould is a sign of a damp bathroom.

Dangers of mould

Moulds are a potential cause of many health problems including asthma, sinusitis, and infections, and may also play a major role in cases of sick building syndrome and related illnesses. The young and elderly are particularly at risk.

Cleaning mould off walls in a constantly damp room will not get to the root of the problem – to do so you should follow the 4 steps listed in this article to limit excess moisture.

Anti-mould paint

Specialist bathroom paints have a superior moisture and steam resistant formula that is perfect for wet and steamy environments, and mould resistant varieties may also contain a fungicide that helps to reduce the risk of mould.

I use this Dulux Bathroom+ paint as it is available locally to me and its always performed well, but there are alternatives available.

Anti-mould silicon

These specialist silicones contain a anti-bacterial solution such as Microban, which prevent mould growth within the silicon for up to 10 years. Some, also contain additives that kill germs such as E-Coli and Salmonella.

I often use Dow Corning but there are others available too, as they are not cheap when compared to other silicones.

Top tip

A major cause of premature development of mould in silicon around baths is hair dye – so clean & dry your bath thoroughly after using hair dyes.Also, clean your bathroom regularly, as even anti-mould silicons will develop mould on top of them if not cleaned properly.

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