What home owners should know:

Dave photo rA modern gas furnace has a life span of about 20 – 30 years. A well maintained furnace is good for 25+ years.

Most furnace filters need to be changed every 3 months. If you have pets or someone who smokes on the premise, change more often.

The size of a gas furnace is most often based on the square footage of the area being heated. 25 – 35 Btu’s per square foot. Definition of Btu: the amount of heat required to raise the temperature of 1 pound of water 1°F.

This is a simple description of the FORCED – AIR HEATING SYSTEM

Forced-Air Heating is a simple two part system consisting of:
1. A furnace.
Definition: an enclosed chamber in which heat is produced to generate warm air, steam, destroy refuse, smelt or refine ores, etc.

In the home the furnace is known as the central heating device.

2. Duct work.
Definition: any tube, canal, pipe, or conduit by which a fluid, air, or other substance is conducted or conveyed.

The duct system is a means of distributing the heated air.

The Furnace
The Furnace has a fuel supply, usually natural gas.

There is a thermostat that turns the fan and the furnace on & off.

There is a combustion chamber where the gas is ignited and heats the air.

There is an exhaust pipe the takes combustion gases to the outdoors.
The Duct System

The fan in the forced-air furnace blows heated air from the combustion chamber into the duct system to distribute and supply warm air to the rooms through heat registers (These are the vents seen throughout a home, within the ceiling, floor or walls in various rooms.)

The cold air travels back to the furnace through a register located centrally, usually in a hallway, into the return air duct, through an air filter that removes dust and other particle and back to the combustion chamber.

We can get into more technical parts to the furnace and duct system but that’s not necessary as this should give you the basic concept of a Forced-Air Heating System.

The furnace heats the air and the duct system distributes the warmed air to the room. The cooled air is returned to the furnace via a return air duct and then filtered and run through the furnace to be reheated and redistributed.

As a last note on this it is now a requirement that a vent for “make up” air exists with most all furnaces.
Definition: Make-up air – fresh outside air brought into a building through ventilating (heating or cooling) equipment. Simply put, air needs to be replenished or “made up” or compensated for the air lost through ventilation.
Dave Silva GC

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