How to install extra ventilation in an old building with new windows?

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Our house is situated in Bavaria. Our energy consultant confirmed that the main expensive roof beams could not be replaced and everything else could be re-insulated and covered.

There is also a plan for new glazing for the house.

The consultant advises triple glazing. But since we don't want to insulate the walls, we will definitely get mold after the new windows are installed, according to the consultant.

To avoid this we have two options:

— Install a ventilation system in each room through the outside wall. This means: drill a hole and install a fan (the worst option will probably be expensive and time consuming).

— Install windows with their own ventilation (would be interesting).

How did you solve the mold problem after installing the new windows and what does your ventilation look like?



If you have to get KfW funding as a separate measure to replace the window, the U-value of the wall should not be lower than the window. This needs to be checked, otherwise there really is a risk of condensation and mold on particularly cold areas of the unmaintained exterior wall. Your energy consultant should know this, especially if he is applying for and supervising KfW measures as a qualified expert.

When replacing windows the ventilation concept according to DIN 1946-6 must also be developed. The required air exchange rate can be achieved, for example, by decentralized ventilation. If necessary, so-called window rebate ventilators installed in the window frame are sufficient. This must be verified by calculation.

You need an energy consultant to work out a concept for the renovation of the building as a whole. All measures must be coordinated with each other and with transitions.


The simple way really can be window rebate fans.

But there are also good decentralized heat recovery ventilation systems. The prices themselves are within reason.


Look for Soleo Air from Höhbauer.

We have Airpur modules in a roller shutter box, and we're happy with them so far.

The Airpur modules cost from 1100 to 1300 euros, depending on whether they are for blinds or shutters.

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