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A furnace is a major piece of equipment, usually located in the attic that is permanently installed to provide heat to an indoor area. In most instances, the heat is generated by a natural gas or common fuel source, and in some situations electrical heating is used. These furnaces always need to be vented to the outside, and in the past this was usually accomplished through a chimney, which would sometimes expel as much of the heat produced as the exhaust. Today, many furnaces are up to 90% efficient and can be operated without a chimney. The small amount of waste gas and heat are mechanically ventilated through a small tube through the side or roof of the house.

Most of today's furnaces use a fan to circulate air to the rooms of the house and pull cooler air back to the furnace for re-heating. While the furnace is a primary component in the heating system, it is actually used all year long as a means to propel both the heated and cooled air by use of a fan. This fan and blower capacity is extremely important to the operation of the system as is the type and design of the ductwork. Stronger capacity furnaces can often times overcome restrictions in the ductwork. In a modern application, separate ducts collect cool air to be returned to the furnace. Once at the furnace, the cool air passes through the furnace, through a filter (if installed), through the blower, through the heat exchanger, where it is finally blown through the building.

The air is propelled through the ductwork, which can be either hard pipe sheet metal or flex duct. Unless the ducts have been sealed using mastic, the ductwork can leak the heated or cooled air into unconditioned areas as it is pushed through.

The Variable-Speed Furnace

This furnace offers improved efficiency over a single speed furnace since it will run in low-fire approximately 80% of the time. It is also one of the quietest furnaces in its class and offers precise control of the airflow in all modes to properly cool, heat and dehumidify the home. Since the furnace runs in low-fire most of the time, the furnace will deliver a more constant, even heating of the home. This furnace is designed for use with two stage cooling and zoned systems.

When your furnace is installed, the speed and airflow for your home are set at the furnace depending upon your specific situation, such as the size of your home, etc. However, there are situations that can occur within the household to restrict this airflow, such as slight deficiencies in the ductwork design, your system's location, undersized return and dirty filters, to name just a few. Variable-speed motors have intelligent technology that monitor incoming data from the blower and adjust accordingly so maximum comfort is felt at all times.

What's inside

The below diagram is to provide an example of what the inside of a 2-stage furnace would look like. Specialty parts and features vary depending on make and model of the furnace, but their basic functions are the same. For more information on the different technologies available, please visit our manufacturer brand page by clicking · · here · ·. View the brands we carry and visit each of their websites to read more about the features unique to their products.

How the Furnace Works

Further Reading

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