General Angela B. Clyne  


Bath ventilation is a great thing! Because there is no better way to prevent the formation of mould – especially in wet rooms. But what can you do if there is no bath ventilation at all and one is to be retrofitted? Is that so simple possible? The answer is basically yes. Bath ventilation can be retrofitted with a manageable amount of effort. The following project shows one of the possibilities for retrofitting a bath ventilation system – namely the installation of a pipe-in-pipe exhaust system in the attic above.


If forced ventilation is mandatory for indoor baths, it is generally not necessary to install it for outdoor baths with a window. However, if the window is not very well positioned due to a pitched roof and is not particularly large, problems with mould can occur. Because if even massive airing does not help any more, must be provided simply technically for the necessary ventilation.

Good planning is the key to such a project. If the bathroom is not to be completely renovated, the work required to install a ventilation system should be kept to a minimum. This is also the case here, where the tiles in the bathroom should not be affected. Read more here about plumbing tips for more details.

With an external bathroom such as this, there would of course be the possibility of making a direct wall breakthrough to the outside and installing a fan or heat exchanger. But even here the pitch of the roof is not an advantage, as the warm moist air naturally collects near the ceiling and not in the area of the wall opening. In addition, no electrical connection is provided near the outer wall, so that such a fan cannot be installed without chiselling tiles. Fortunately, the bathroom is on the upper floor of the house. In addition, the ceiling is a drywall construction, so a ceiling breakthrough does not require much effort. The electrical installation is also accessible via the attic, so this variant has clear advantages over all other solutions.

In this project, a poppet valve is therefore installed in the shower area, which leads the air into the attic via ventilation pipes. Ventilation is provided by a pipe-in-pipe fan connected to the bathroom light switch in the attic. This ensures that no electrical installation is used in the shower area and that noise pollution is reduced to the air flow.


In order to be able to install such a bath ventilation system retrospectively, of course some tools and material are needed. A cordless screwdriver, a jigsaw, a screwdriver, an iron saw as well as the obligatory tape measure must not be missing. For the preparation of the electrical connections, there should also be a test lamp, a side cutter and stripping pliers. Depending on the setting, you will need a four-pole cable, an empty pipe, clips, lots of wagon clamps and possibly also one or two damp-proof boxes of electrical material.

The material list for the ventilation of the bathroom is also not without its features: In addition to the fan used (here a pipe-in-pipe fan), a poppet valve, two connection pieces, two 50 cm long ventilation pipes, a flexible pipe, two pipe connectors, a sealing tape for ventilation, two pipe clamps, two 45° bends and a 90° bend should be available. All pipes as well as the required accessories were dimensioned with a diameter of 100 mm. This is sufficient for an exhaust air capacity of up to 250m³ per hour. An 8 m² bathroom with a room height of 2.5 m and six air changes requires just 120 m³ per hour. The piping is therefore sufficiently dimensioned.


Of course some preparations have to be made before the work can begin. On the one hand there would be the laying of the electrical installation; on the other hand the uncovering of the ceiling opening in the attic and the protection of the existing equipment. The former is not described in detail in this project, as it would not only go beyond the scope of this manual, but would also be best installed by a specialist. It is important to note that the following wires must be provided at the planned location of the fan: These would be both the switched wire of the bathroom lamp, but also an unswitched phase including earthing and neutral conductor.

The unswitched phase is necessary in order to also be able to connect a follow-up relay, so that the fan does not switch off simultaneously with the light, but can continue to run for a certain time. Of course, it would also be possible to install another switch for the fan, but at least this would be connected with some caulking again.

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