I would think it is condensation, dod they put !trickle vents! into the new windows? if not you can try leaving them on the first catch of the latch this will allow some fresh ait into the rooms, also if the old fire places have been covered over make sure the vents are slightly open, it might be worthwhile installing a humidity controlled fan in the bathroom and leaving doors open, this will help a lot, there are also some really good systems about for curing condensation I have fitted many systems similar to this type, take a look they are easy to have installed, good luck, Ray
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