Efficiency:
Modern natural gas furnaces achieve operating efficiencies as high as 96 or 97 percent AFUE (Annual Fuel Utilization Efficiencies) and thus give the homeowner 96 cents worth of heat into the living area for each dollar of gas purchased. The minimum efficiency standard for furnaces sold in the U.S. is 78 percent. While the typical furnaces of years past used chimneys, the high efficiency units of today extract so much heat from the gas they use that they can be vented through the sidewall of your home using plastic pipe. This venting is similar to the type of venting associated with a clothes dryer.

Pilot lights, which were used in older equipment, have been replaced with spark ignition systems to save energy.

Features:
Forced air natural gas furnaces come in several configurations:

• Upflow models are typically installed in a basement to heat a one or two story dwelling. Warmed air from this unit exits at the top and continues traveling upward and away from the unit.
• Downflow models can be installed in the first floor area of a home, mobile home or modular housing unit. The heated air from this furnace exits at the bottom and is pushed under the floor area to be distributed by ductwork throughout the home.
• Horizontal models may be installed in an attic or crawl space. These types pull cool air in the one end and exhaust heated air out the other end of the unit.

A boiler is able to use two or more thermostats along with control valves to provide different temperature settings simultaneously to different floors or living areas in your home. Modern boilers are able to provide domestic hot water to be used in your home. They circulate the heated boiler water through a coil that is submerged in a tank filled with water. As the heated water travels through the coil, it gives up its heat and makes hot water that can now be used anywhere in the home.