With heating systems, the efficiency of a furnace is determined by is AFUE (Annual Fuel Utilization Efficiency); a gas furnace’s efficiency in converting fuel to energy. The higher the AFUE, the more energy efficient the furnace is.

A gas furnace with an 80% AFUE rating means that 80 cents of every $1.00 of heating energy expense warms the home. A gas furnace with a 95% AFUE rating means that 95 cents of every $1.00 of heating energy expense warms the home. 95% AFUE furnaces are more energy efficient.


What is a Furnace?

A household heating furnace is a permanent installation within a home that provides heat for the interior space. This is done using an intermediary fluid -often air or steam- moving through the system. However, a modern furnace would be running on natural gas, liquefied petroleum gas, oil, coal or wood. In cases where the electricity costs are low, there are some furnaces that could use electricity.


How a Gas Furnace Works

A gas furnace (referred to as a gas forced-air furnace system) is activated by the thermostat when it detects a drop in room temperature below the set level. The thermostat will send an electrical signal to a relay within the furnace to open a valve, move natural gas to the burners and turn the blower on. The burners are lit using a pilot light or ignition light inside the furnace creating heat within a metal chamber called the heat exchanger through which the air circulates.

Once the air is heated in the heat exchanger, it is pushed through a hot-air plenum before going out through the ducts into the room. The gases created during combustion by the burners are moved out through a chimney in the roof. For highly efficient furnaces, however, these gases can be vented through the wall.


Types of Furnace

There are three types of furnace:

  • Single-stage furnaces

These usually have a single operation stage, either on or off, hence the name ‘single-stage’. Due to this, the furnace is rather noisy and always runs at maximum speed pumping the hot air out. However, it is inexpensive to purchase and install due to the simple technology involved.

  • Two-stage furnace

This type has two operation stages i.e. full speed and reduced/half speed. This means that they can run at a lower speed depending on how much heating is required, thereby keeping the house at the desired temperature. They are also quieter since the air doesn’t move through at as high a velocity as it does in case of a single-stage furnace.

  • Modulating furnaces

These can constantly regulate the amount of heat being released along with the velocity of the air passing through. This allows you to save more on energy costs than you would with either of the other furnaces and gives you better control of the temperature inside the house.


Advantages of a furnace system

There are several advantages of having a furnace system. These include:

1.Multipurpose ducts

With furnace systems, the ductwork functions to deliver the heated air into the room. However, they can also bring in cool air during warmer seasons, so you can install an air conditioning system as well if you have a furnace.

2.Easy parts and repairs

Furnaces are common in most homes so in case of repairs or replacement, you can easily find spare parts.

3.Energy efficient

The fuel efficiency of a gas furnace is measured in Annual Fuel Utilization Efficiency (AFUE). Most of the gas furnaces available today have AFUE ratings of over 90% and electric furnaces have 100% AFUE ratings. This means that you will not only be saving on the cost of energy utilization but also caring for the environment.

4.Faster heat

Natural gas heats quickly so if you have a furnace, your home will be heated up rather quickly, meaning you won’t have to turn on your heating system hours earlier to ensure that your home is at the right temperature before you walk in.

Furnace system troubleshooting

Usually, when the temperature of a furnace goes above the maximum required threshold, a thermostat will shut it down. If there is a problem with your furnace, it will keep being shut down before your house has reached the desired temperature. It often means that your furnace’s high limit temperature setting is too close to its normal operating temperature, so you should adjust it upwards.

Alternatively, the humidifier may be poorly installed on the furnace so the duct may be returning too much of the humidified air back into the furnace, thereby raising the temperature in the furnace. The solution is to reduce the size of the cross-feed tube or put in a baffle that reduces the amount of air that’s going back into the furnace.

Note: There are higher efficiency models than 95% and different motor/stages types. The different motor types also increase efficiency and can be communicating with the AC to improve efficiency even further.