There are a few different furnaces on the market that manufactures make for homes. Understanding how your furnace works will equip you with the knowledge needed to perform safe maintenance on it or when you choose to purchase a new one. The main parts of a furnace are:

• Gas Fired Burner
• Heat Exchanger
• Blower Motor
• Air Ducts
• Thermostat

Electric furnaces will be talked about later on, so let’s dive into how most homes are heated in North American, especially in Ontario Canada.

Gas Fired Furnaces

The most common furnace a home has in the colder regions of North American is the gas fired, forced-air furnace. Let’s unpack what that means, a gas fired furnace refers to the fuels it burns to generate heat, these fuels come in gas forms. Propane or Natural Gas, natural is a misnomer as the fuel is a byproduct when oil is extracted. The surrounding layers of earth around oil contains this natural gas and is used to power a furnace’s burner.

The burner within a furnaces is measured in BTUs.

British Thermal Unit

BTU for short, is a measurement unit for how much natural gas it takes to generate heat or heat water. The math behind the calculation is rather complicated, so for simplicity’s sake, 1 btu produces 15C. Gas fired furnaces come in different BTU ratings and are most commonly in:

• 40,000 BTUs
• 60,000 BTUs
• 80,000 BTUs
• 100-120,000 BTUs

The bigger the home, the more BTUs is needed to heat the home. But the size of the home alone does not give an accurate indication of the size of the furnace needed because the air flow throughout the home plays a major role on how well a home is heated. Other factors like insulation, window types and the house’s foundation also play a role in determining the size of a furnace.

Forced Air Furnaces

A gas fired furnace is the same as a forced air furnace. The Gas Fired Burner in the furnace produces heat which raises the temperature of a serious of metal tubes called a Heat Exchanger.

Then, unheated air is blown across the heat exchanger by a furnace’s Blower Motor and the higher temperature from the Heat Exchanger is transferred to the passing air. The now heated air travels through a series of circular or rectangular metal prisms called Air Ducts which are made out of sheet metal.

It is very likely you can see the air ducts in your home, either on the basement ceiling or coming off the furnace, but they are also hidden inside your home’s floors and walls as well.

Air Ducts

These long gray metal boxes have two purposes in your home, one set of vents hold unheated air (Cold Air Returns) and the other set hold heated Supply Air. All air ducts end in a register or vent that is fixed to a floor or wall of a home. The registers are often be opened and closed to dampen the amount of heat coming into a room. This gives furnaces another name, a ducted furnace, that is to say the furnace uses air to distribute heat.

A ductless heating system is possible and will be covered later. Back to things that blow.

Air Flow

The amount and speed of air traveling through a vent is measured in CFMs. The Cubic Feet Per Minute of your furnace needs to be calibrated based on the size of your home and its duct work and this could range anywhere from 400 CFMs to 1200 CFMs needed to efficiently run heat your home.

The blower motor in your furnace is very often big enough to handle your home’s needs, but the size of the duct work and its configurations may be improperly built.  If a ducted furnace has incorrectly built duct work, it will not matter how powerful the furnace’s blower motor is. Most heating issues come from insufficient return airs ducts going to your home’s furnace.

We highly recommend you consult with an HVAC expert when replacing or repairing your furnace, they will be able to determine if you have an air flow issue.

Measuring Your Home’s Size for HVAC Equipment

No two houses are the built the same so every home should be measured for its residential heating and cooling load which then corresponds to the Furnaces BTU rating and the air conditioners tonnage.

There is a long list of things that are measured in this calculation and the major items included are:

• Windows
• Doors
• Insulation Type
• Direction of Sun
• Size of Rooms
• Number of occupants

If you are trying to determine the size of the furnace & ac for a home, the cooling load will take priority over the heating load. That is to say you are sizing for cooling first and foremost. This heat loss/gain measurement has a margin of error 10%.

Thermostats

The thermostat is really just a switch that tells the furnace to turn on or off. If the temperature you have set is higher than the temperature in the home, it should be telling the furnace to turn on. If the system isn’t working, perform these simple steps to verify the thermostat is working properly. Try this:

▢  Ensure the thermostat is switched to heating mode. If it is, try switching it to off, then back to heat. This will create a temporary reset for the furnace and bypass any minor issues

▢  Raise the temperature by a couple of degrees to ensure it is calling for heat

▢  Replace the batteries. All to often we see thermostats which can no longer function due to lack of power in the batteries

▢  Wait & see if warm air is coming from the registers

In this day and age, there are basic models that simply communicate to the furnace, and their are up-scale models that are Wi-Fi and smart home enabled. In the case a home uses a hybrid furnace/heat pump system, the thermostat will need to support communicating the