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HVAC Systems & How They Work

Types of Fuel

Heating oil/ diesel / Kerosene - Petroleum based fuels became popular for home heating in the 1920 (along with the invention of the thermostat). According to the American Petroleum Institute new oil heating systems boast energy efficiency ratings ranging from 83 to 94 percent, and over 8.5 million American households, mostly in the Northeastern states, rely on heating oil to keep warm in winter. Heating oil is typically stored in a steel tank somewhere in the home. Tanks can be located above ground, in the basement or buried in the ground. A typical house tank is 275 gallons.

Natural Gas - Natural gas, in itself, might be considered an uninteresting gas – it is colorless, shapeless, and odorless in its pure form. Quite uninteresting – except that natural gas is flammable, abundant in the United States, and when burned it gives off a great deal of energy with fewer emissions than many other sources. In the 1960s, the construction of thousands of miles of pipeline in America provided the foundation for the transportation of natural gas. New uses for natural gas were discovered, these included using natural gas to heat homes and operate appliances such as water heaters, ovens, and cooktops. Natural gas runs from the main into a home in what's called a service line. When the gas passes through a customer's gas meter, it becomes the property of the customer.

Propane/LPG - Propane is a hydrocarbon and is sometimes referred to as liquefied petroleum gas, LP-gas, or LPG. Propane is produced from both natural gas processing and crude oil refining, in roughly equal amounts from each source. Nearly 97 percent of propane consumed in the United States is produced in North America. It is nontoxic, colorless, and virtually odorless. To fuel homes, large tanks can be buried underground because propane is a nontoxic, nonpoisonous fuel that doesn’t contaminate aquifers or soil. Refueling a propane vehicle takes about the same time as refueling a gasoline vehicle. And propane is the only alternative fuel with fueling stations located in every state.

Forced Air System

This system is by far the most common type of home heating and cooling system. An appliance fired by gas, oil, or wood in which air is heated to be circulated throughout a building in a heating system. Air distributed from furnace through ductwork and into room by registers.

Fuel Sources - natural gas, propane, oil or electricity


  • Duct system can also be used for cooling
  • Air may be filtered to improve air quality
  • Furnace can attain highest AFUE (efficiency) than boiler systems


  • Fan or blower can often be heard when running
  • Moving air can distribute allergens.
  • Can be considered drafty and have more temp fluctuation

Hot Water Baseboard or Radiator System

A boiler is the heating plant used to create hot water or steam for hydronic baseboard, radiant heat or steam radiator heating systems. Steam boilers are more complex than hot water boilers and have special gauge glass, pressure gauges, blow off valves and automatic feeds. Hot water is heated by the boiler and piped to "fin-tube" baseboard units or cast iron radiators mounted along walls. The fins in baseboards increase the surface area of heat dissipation making the unit more efficient.

Air is distributed by convection as air rises and is heated by the baseboard or radiator unit.

Fuel Sources - Boiler may be fueled by natural gas, propane, oil or electricity


  • Energy efficient
  • Quiet
  • Close temperature control creating a more constant, even heat


  • Baseboard radiation / convection units must remain unobstructed and can provide challenges in furniture placement and drape design.
  • Slow temperature increase.
  • Air conditioning requires a separate ductwork distribution and cooling system.

Steam Radiant Heating System

Steam radiators are nostalgic and not often used today. They are characterized by cast iron upright radiators radiating heat with steam. Steam systems come in two varieties, one-pipe and two-pipe systems. With one-pipe systems the water and steam travel in the same pipe but in opposite directions. In two-pipe systems steam flows in one pipe and water condensate returns in another set of pipes. Heat is distributed with steam piping and radiator units.

Fuel Sources - Steam boiler may be fueled by natural gas, propane, oil or electricity


  • Efficient and warms spaces quickly
  • Radiant heat is comfortable
  • Old hot water system radiators can now be replaced with smaller convection units or vertical wall panel radiators


  • Radiators can be unsightly
  • Radiator locations may limit furniture placement and window coverings
  • Air conditioning requires a separate ductwork distribution and cooling system.


The newest home heating (and cooling) technology is called a Geothermal Heat Pump (GHP). Heat pumps work like a refrigerator that can run in reverse. Heat is taken from one source and deposited in another location. With ground loop geothermal systems, heat is taken from or deposited to the earth by use of a ground loop pipe.

The EPA states that a Geothermal Heat Pump can save 30 to 70 percent on home heating and 20 to 50 percent on home cooling costs over conventional systems. But these systems are not cheap.

Air Conditioner

Air conditioners use chemicals (commonly called refrigerant or Freon) that easily convert from a gas to a liquid and back again. This chemical is used to remove heat from the air inside of a home to the outside air. Air conditioners and refrigerators work the same way. Instead of cooling just the small, insulated space inside of a refrigerator, an air conditioner cools a room, a whole house, or an entire business.

Heat Pump

A heat pump is an air conditioner that contains a valve that lets it switch between "air conditioner" and "heater." When the valve is switched one way, the heat pump acts like an air conditioner, and when it is switched the other way it reverses the flow of the liquid inside the heat pump and acts like a heater.

Air conditioners and heat pumps are designed for the size of the space needed. An accurate calculation will keep installation and operating costs down. If an AC is too small, it will not cool the space to comfortable levels in extreme weather. Air conditioners that are too big use more electricity and leave the air in your house with excess humidity.

Ban on Production and Imports of Ozone-Depleting Refrigerants

In 1987 the Montreal Protocol, an international environmental agreement, established requirements that began the worldwide phase-out of ozone-depleting CFCs (chlorofluorocarbons). These requirements were later modified, leading to the phase-out in 1996 of CFC production in all developed nations. In 1992 the Montreal Protocol was amended to establish a schedule for the phase-out of HCFCs (hydrochlorofluorocarbons). HCFCs are less damaging to the ozone layer than CFCs, but still contain ozone-destroying chlorine.

HCFC-22 (also known as R-22) has been the refrigerant of choice for residential heat pump and air-conditioning systems for more than four decades. Unfortunately for the environment, releases of R-22, such as those from leaks, contribute to ozone depletion. In addition, R-22 is a greenhouse gas and the manufacture of R-22 results in a by-product (HFC-23) that contributes significantly to global warming. As the manufacture of R-22 is phased out over the coming years as part of the agreement to end production of HCFCs, manufacturers of residential air conditioning systems are offering equipment that uses ozone-friendly refrigerants.

R-410A has replaced R-22 as the preferred refrigerant for use in residential and commercial air conditioners in Japan, Europe and the United States

R-410A (which contains only fluorine) does not contribute to ozone depletion, and is therefore becoming more widely used, as ozone-depleting refrigerants like R-22 are phased out. However, it has a high global warming potential (2088 times the effect of carbon dioxide), similar to that of R-22. Since R-410A allows for higher system efficiencies than an R-22 system, by reducing power consumption, the overall impact on global warming of R-410A systems will be substantially lower than that of R-22 systems due to reduced greenhouse gas emissions from power plants

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