The traditional way to deal with condensation is to open the windows a tiny bit. It works really well and costs nothing - heat loss is probably less than cost of running a de-humidifier. It also refreshes the air and is good for you. But you will always have some condensation with ali windows due to cool surfaces. Wiping off with a sponge would be more sensible than running a de-humidifier indefinitely. Nobody had ever heard of de-humidifiers until double glazing with draught proof seals became the norm along with condensation, stuffy rooms, sick building syndrome, respiratory problems, mould growth etc. cheers
Jacob