the heat is supplied from the surrounding environment, with only 15–30% as electrical consumption. Environmental aspects From an energy-efficiency standpoint considerable heat gets lost or goes to waste if only a single room needs heating, since central heating has distribution losses and (in the case of forced-air systems particularly) may heat some unoccupied rooms without need. In such buildings which require isolated heating, one may wish to consider non-central systems such as individual room heaters, fireplaces or other devices. Alternatively, architects can design new buildings which can virtually eliminate the need for heating, such as those built to the Passive House standard. However, if a building does need full heating, combustion central heating may offer a more environmentally friendly solution than electric resistance heating. This applies when electricity originates from a fossil fuel power station, with up to 60% of the energy in the fuel lost (unless utilized for district heating) and about 6% in transmission losses. In Sweden proposals exist to phase out direct electric heating for this reason (see oil phase-out in Sweden). Nuclear, wind, solar and hydroelectric sources reduce this factor. In contrast, hot-water central heating systems can use water heated in or close to the building using high-efficiency condensing boilers, biofuels, or district heating. Wet underfloor heating has proven ideal. This offers the option of relatively easy conversion in the future to use developing technologies such as heat pumps and solar combisystems, thereby also providing future-proofing. Typical efficiencies for central heating (measured at the customer's purchase of energy) are: 65–97% for gas fired heating; 80–89% for oil-fired and 45–60% for coal-fired heating. Oil storage tanks, especially underground storage tanks, can also impact the environment. Even if a building's heating system was converted from oil long ago, oil may still be impacting the environment by contaminating soil and groundwater. Building owners can find themselves liable to remove buried tanks and the remediation costs. See also District heating Energy conservation Forced air Forced-air gas Geothermal systems Hearth Heating, ventilation, and air conditioning (HVAC) Hydronics Oil heater OpenTherm Renewable energy Solar combisystem Thermostat Underfloor heating Water heating Wind energy Outdoor wood heaters Uniform Mechanical Code Passive house References Sources Further reading Adams, Sean Patrick. Home Fires: How Americans Kept Warm in the 19th Century (Johns Hopkins University Press, 2014), 183 pp External links BBC Wales History – Life before central heating Plumbing Residential heating Greek inventions Ancient Greek technology