and volume stored, and in the case of heat pumps to reduce the size and investment in heat pump, heat sink and electricity costs. Two main types of improvement can be made to a building's energy efficiency: Insulation Improvements to insulation can cut energy consumption greatly, making a space cheaper to heat and to cool. However existing housing can often be difficult or expensive to improve. Newer buildings can benefit from many of the techniques of superinsulation. Older buildings can benefit from several kinds of improvement: Solid wall insulation: A building with solid walls can benefit from internal or external insulation. External wall insulation involves adding decorative weather-proof insulating panels or other treatment to the outside of the wall. Alternatively, internal wall insulation can be applied using ready-made insulation/plaster board laminates, or other methods. Thicknesses of internal or external insulation typically range between 50 and 100 mm. Cavity wall insulation: A building with cavity walls can benefit from insulation pumped into the cavity. This form of insulation is very cost effective. Programmable thermostats allow heating and cooling of a room to be switched off depending the time, day of the week, and temperature. A bedroom, for example, does not need to be heated during the day, but a living room does not need to be heated during the night. Roof insulation Insulated windows and doors Draught proofing Underfloor heating Underfloor heating may sometimes be more energy efficient than traditional methods of heating: Water circulates within the system at low temperatures (35 °C - 50 °C) making gas boilers, wood fired boilers, and heat pumps significantly more efficient. Rooms with underfloor heating are cooler near the ceiling, where heat is not required, but warmer underfoot, where comfort is most required. Traditional radiators are frequently positioned underneath poorly insulated windows, heating them unnecessarily. Waste-water heat recovery It is possible to recover significant amounts of heat from waste hot water via hot water heat recycling. Major consumption of hot water is sinks, showers, baths, dishwashers, and clothes washers. On average 30% of a property's domestic hot water is used for showering. Incoming fresh water is typically of a far lower temperature than the waste water from a shower. An inexpensive heat exchanger recovers up on average 40% of the heat that would normally be wasted, by warming incoming cold fresh water with heat from outgoing waste water. Heat recovery ventilation Heat recovery ventilation