How Your Heating System Works – Part 2: Furnaces


Earlier this month, we told you about the inner workings of water and steam boilers. Today our “How Your Heating System Works” series continues as we explain the different types of furnaces. Like a boiler, a furnace uses a flame to heat a heat exchanger inside a combustion chamber. The difference is that the furnace heats air and blows it directly into the indoor spaces to mix with the cooler air in each room and raise the overall temperature. (In a water or steam boiler, hot water or steam heats baseboards or radiators, which radiate heat into the rooms.) See if this process sounds familiar:

1. The thermostat sends a signal to the controls on the oil burner.
2. Fuel is sent to the burner through a fuel pump. A nozzle then atomizes the fuel into a mist, which is sent into the combustion chamber.
3. The mist is mixed with air and ignited. This will cause the combustion chamber to get very hot.
4. A heat exchanger will allow air to absorb the generated heat and propel it via a blower throughout the home’s ducts.
5. Emissions from the system’s combustion are sent through the flue pipe and out the chimney.

There are, however, many different factors to consider when determining which furnace is right for your home. For example, you can decide between:

Two Stage vs. Multiple Speed Furnaces:

o  Two Stage Furnace: A two stage furnace operates only as either on or off. As soon as the furnace receives an indication that the temperature has dropped below the set level, the furnace turns on at maximum capacity to heat the room as quickly as possible.
o  Multiple Speed Furnace: Unlike two stage furnaces, with multiple speed furnaces, “on” doesn’t just mean “on”. These furnaces typically have two different levels of power and about 80% of the time, they run on the lower power setting. Multiple capacity levels generally lead to a tremendous increase in fuel efficiency and to lower heating bills.

In some furnaces, the blower motor can run at virtually any speed, creating what is known as a variable speed furnace. This type of furnace allows the blower to adjust its output speed depending on your home’s heating needs. This further increases fuel efficiency and helps reduce the noise made by the furnace. The blower on a variable speed furnace can also continue to circulate air, even when it isn’t being heated. When an air cleaning system is used with the furnace, it will help decrease the presence of allergens in your home and increase your home’s indoor air quality. In most homes that have central air conditioning, the same blower is used for both heating and cooling.


To read more about the inner workings of your boiler and the benefits of energy efficient systems, visit