A Allan of Milton asks :-

During the winter I have had condensation under the toilet cistern and puddles of water on the toilet floor. Is this due to a recently installed heat pump and, if so, why is the dampness occuring now?

Gerry Carrington, a physicist specializing in energy at Otago University, responded.

You are probably keeping your house warmer than before. Moisture in the air is most likely to condense in the coldest place in the house. In your situation this is the toilet cistern because this is filled with cold water after use, whereas the rest of the house is now being well heated. In time the condensate will build-up on the cold cistern surface and droplets will run down, eventually producing a puddle on the floor.

Why did this not happen previously? There are several possible reasons. One is that the house and contents are drying out now because the temperature has recently increased. This would increase the amount of moisture in the, now warmer, air, leading to condensation on the cold cistern.

Alternatively, perhaps there are activities like cooking and showering that produce steam without using enough ventilation. In the past this moisture may have condensed in different locations around the house, less obvious than the toilet cistern. In any case the problem is due to the cold toilet cistern in a well heated house, not the heat pump.

So what should you do? First, keep the toilet door closed and use an extractor fan when cooking or showering. Second follow EECA’s Energy Spot advice: the simplest and cheapest way to ventilate your home is to open doors and windows regularly – at least for a few minutes each day – to allow fresh air from outside into your home.