Boiler

• A boiler is used in homes and buildings that use water as "fuel" for heating. The boiler heats the water to a temperature of 180 degrees Fahrenheit, thereby generating steam. Pipes distribute the steam to radiators or radiant flooring heat systems. While boilers come in both water and steam versions, water boilers are most common. While it is not common, it is possible to connect a boiler to a forced air heating systems. In this set-up, hot water coils serve as the heat exchanger. There are also alternative (albeit somewhat complicated) ways to set up a boiler as both a furnace to provide both heat and hot water. But keep in mind that the latter two examples are exceptions to the rule and require professional conversions and installations.
  
  

Furnace

• Where water is the "fuel" for boilers, furnaces are fueled by natural gas, liquid propane gas, electricity or coal. The majority of homes use gas. Furnaces heat air, and blowers distribute and force the warmed air through the duct channels, using a forced air system. The duct channels end at vents located on baseboards, ceilings and walls and empty the warmed air into the room where the vent is located. Homes heated with furnaces outnumber homes heated with boilers. The popularity of using furnaces for heating systems took off during the 1960s. This is when many homeowners began to convert to natural gas for heating, versus using radiators and boilers and using coal. Next to natural gas, electricity is the second most popular choice for powering furnaces, followed by coal. However, the use of coal is spotty outside the Northeastern areas closest to Pennsylvania and the Virginias, where coal supply sources are plentiful.
  
  

Conversion Considerations

• While it certainly is possible to go from a furnace to a boiler and vice versa, it can be quite costly and complicated. A pre-existing pipe system for boilers would have to be scrapped and swapped out for an entire new duct and vent system. When homeowners convert a boiler to a furnace, they usually go all the way and install a central forced air HVAC system to handle both heating and cooling needs.
  
  

New Equipment and Efficiency Considerations

• Furnaces and boilers manufactured after 2006 have greatly improved in efficiency. If you are replacing a boiler or furnace, take advantage of the new efficiencies by focusing on Energy-Star and High Efficiency labeled and rated units. New furnaces not only have improvements in efficiency but also in the technology used to manufacture the units. Focus on the Annual Fuel Utilization Efficiency rating when furnace shopping. Look for a furnace with a capacity of 50,000 to 125,000 British Thermal Units per hour, which is the standard range used in most homes today.