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http://en.wikipedia.org/w/index.php?title=HVAC&action=edit&s Central heating unit "Heaters" redirects here. For the community in the United States, see Heaters, West Virginia. "Heater" redirects here. For other uses, see Heater (disambiguation).

A heater is an object that emits heat or causes another body to achieve a higher temperature. In a household or domestic setting, heaters are usually appliances whose purpose is to generate heating (i.e. warmth). Other types of heaters are Ovens and Furnaces.

Heaters exist for all states of matter, including solids, liquids and gases. There are 3 types of heat transfer: convection, conduction and radiation.

The opposite of a heater (for warmth) is an air cooler (for cold) (see air conditioning) used to keep the user cooler than the temperature originally surrounding them.

There are many different types of heating systems. Central heating is often used in cool climates to heat houses and public buildings. Such a system contains a boiler, furnace, or heat pump to warm water, steam, or air in a central location such as a furnace room in a home or a mechanical room in a large building. The use of water as the heat transfer medium is known as hydronics. These systems also contain either duct work for forced air systems or piping to distribute a heated fluid to radiators to transfer this heat to the air. The term radiator in this context is misleading since most heat transfer from the heat exchanger is by convection, not radiation. The radiators may be mounted on walls or installed within the floor to give floor heat.

Most modern hot water boiler heating systems have a circulator, which is a pump, to move hot water through the distribution system. This distribution system can be via radiators, convectors (baseboard), hot water coils (hydro-air) or other heat exchangers. The heated water can also supply an auxiliary heat exchanger to supply hot water for bathing and washing.

Warm air systems distribute heated air through duct work systems of supply and return air through metal or fiberglass ducts. Many systems use the same ducts to distribute air cooled by an evaporator coil for air conditioning. The air supply is typically filtered through air cleaners to remove dust and pollen particles.

One type of heat source is electricity, typically heating ribbons made of high resistance wire. This principle is also used for baseboard heaters, and portable heaters. Electrical heaters are often used as backup or supplemental heat for heat pump (or reverse heating) systems.

The heat pump gained popularity in the 1950s.[where?] Heat pumps can extract heat from the exterior air (air source) or from the ground (ground source). Initially, heat pump HVAC systems were used in moderate climates, but with improvements in low temperature operation and reduced loads due to more efficient homes, they are increasing in popularity in other climates. Heat pumps can be air to air, air to water, water to air and water to water systems. Water on the supply side of the heat pump is typically geothermal energy from ground water, either surface water or PEX tubing buried in a trench. Due to the construction of wells and site work, geothermal systems are typically more expensive to purchase and install than conventional heating systems.[citation needed]

The invention of central heating is often credited to the ancient Romans, who installed systems of air ducts called hypocausts in the walls and floors of public baths and private villas.[10]

The use of furnaces, space heaters and boilers as means of indoor heating may result in incomplete combustion and the emission of carbon monoxide, nitrogen oxides, formaldehyde, volatile organic compounds, and other combustion byproducts. Incomplete combustion occurs when there is insufficient oxygen; the inputs are fuels containing various contaminants and the outputs are harmful byproducts, most dangerously carbon monoxide which is a tasteless and odorless gas with serious adverse health effects.[11]

Without proper ventilation, carbon monoxide can be lethal at concentrations of 1000 ppm (0.1%). However, at several hundred ppm, carbon monoxide exposure induces headaches, fatigue, nausea, and vomiting. Carbon monoxide binds with hemoglobin in the blood, forming carboxyhemoglobin, reducing the blood's ability to transport oxygen. The primary health concerns associated with carbon monoxide exposure are its cardiovascular and neurobehavioral effects. Carbon monoxide can cause atherosclerosis; the hardening of arteries, and can also trigger heart attacks. Neurologically, carbon monoxide exposure reduces hand to eye coordination, vigilance, and continuous performance. It can also affect time discrimination.[12]

Forecasting is a method of controlling building heating by calculating demand for heating energy that should be supplied to the building in each time unit.ection=2