What size do you need
Compressor models are usually rated at 30°C and 80% relative humidity (RH), a standard test point for comparing machines, not the conditions in a British home. At 20°C and 60% RH a machine typically collects around half its rating, and less in a cold hallway. As a rough guide, 10 to 12 litres suits a flat, 20 litres a three or four bedroom house, and 25 litres or more a larger or damper house.
Compressor or desiccant
A compressor model condenses water on a cold coil, suits a heated house and typically draws 150 to 300 watts. A desiccant model soaks moisture into a heated absorbent wheel, so it keeps working in a cold garage, loft or boat and warms the room slightly, but draws around twice the power. Its rating is usually taken at a cooler 20°C and 60% RH, so a 7.5 litre desiccant does the work of a compressor model rated much higher.
Laundry drying and running cost
Laundry mode usually runs the machine flat out, ignoring the humidity setting, so put it in a small room with the door shut and the airer close by. Even then a compressor model draws a few hundred watts, against a couple of thousand for a vented or condenser tumble dryer. Day to day, leave the humidistat at around 50 to 55% so it switches itself on and off, use the timer to keep it quiet overnight, and rinse the dust filter every few weeks.
