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Heating modern buildings is one of the most important functions that HVAC systems can provide. The energy required to heat a space or a house comes from either the burning of natural gas, or it comes from electric heating loads. The method of distributing heat throughout a building can also vary, depending on the medium used to transport the heat. Usually forced air or water is used, though some heating loads, such as baseboard heaters, rely on passive heat dissipation.
Control of heating loads requires temperature sensitive switches, called thermostats, which can either directly, or indirectly control the heating equipment.