I have a problem of condensation and humidity on some walls (cold walls) and corner ceilings and I am offered to install a central air treatment (CTA) to solve this problem: price 3700 euros. What do you think?
The limited condensation problems on a cold wall are often solved by a simple surface insulation with a thin insulation, type Depron. Start with this before you incur a large fee. Ventilation can often be restored by simple air vents (natural ventilation) provided they do not block them... I imagine that you are offered a system putting your parts overpressure. It is a good system in the old habitat.
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