A furnace is one of the vital requisites for our homes to make sure that the place stays warm and comfortable. The decision to have one requires thorough research as most of us know that the choice we make will have its implications for quite a long run.

There are different types of heating systems available to choose from, say furnace is one option, boiler is another option, some areas (where electricity cost is low) prefer electric heaters (like baseboard heaters or forced fan heaters), where as some other homes prefer heat pumps to produce & transfer heat. In this article we discuss about furnace based heating systems – where a central furnace is used to produce heat (from a fuel source like natural gas, lpg or propane or other fuels) and the heat is then distributed to various rooms through a channel (often a duct based system).

A majority of homes in North America (USA & Canada) uses furnace based heating system. A central furnace produces heat by burning fuel (which could be natural gas, lpg, propane or oil) and warms up the interiors of the home via an intermediary fluid movement through a distribution channel.The fluid in movement would be hot/warm air in the case of most furnaces. 

Note: If the intermediary fluid is steam or hot water, then the heating system would be called as boiler (not a furnace).

 The furnaces used at our homes are usually designed keeping convenience-of-use in focus. Modern-day furnace systems are designed for optimum energy and fuel efficiency so that the bill is not overburdened. A typical modern furnace is upto 98% efficient (where as the older models were only 80% efficient) 

The heat distribution mechanism

Heat is distributed in different ways in a furnace and a boiler. A furnace always distributes heat via air medium (as warm air) through ducts from the central furnace to other areas. A fan/blower is used to force the “warm air” from furnace area to all other interior spaces. Such systems are usually called ‘forced air’ distribution systems. A boiler uses hot water or steam to distribute heat from central boiler to all other interior areas.

 In case of the forced air systems, ducts are used to distribute the air. The ‘duct work’ begins from the central furnace and traverses to each and every room where heating/air conditioning is required. A fan/blower forces the ‘warm air’ from central furnace through the duct work. The ‘warm air’ expands on course, and the ‘cooler air’ is collected (with help of another fan) back to furnace for reheating. In America, separate ducts are used to transfer ‘warm air’ from furnace and  to collect ‘cooler air’ back to furnace. This practise brings an advantage of using the same duct work for air conditioning as well.

At the furnace, the cool air passes through an air filter (to filter out unwanted dust and particles), then the blower and passes through the furnace heat exchanger – where the ‘warm air’ is created and then blown to different rooms with the help of another blower. As I said, separate ducts are used to  blow ‘warm air’ and then to collect ‘cool air’. This makes it very easy to install an air conditioner simply by adding a cooling coil at the outlet of the furnace.

Air is circulated through ‘ductwork’ – where the ducts would be made of sheet metal or flex plastic material. The ductwork should be covered and insulated completely to avoid wastage of heat while traversing . Insulating the ductwork directly affects the efficiency of furnace based system.


Types of Furnaces

Heating furnaces are available in many types and categories to heat our homes. The constant improvements in these furnaces improved the functionality from time to time and also make these furnaces easy to use and control. The two most traditional options that we all are aware of are the electric and gas furnaces. These electric and gas furnaces are also categorized differently to suit the needs of the users. The gas furnace, as the name, indicates, completely dependent upon the fossil fuel to keep it running. These furnaces are quiet yet efficient and have been in use in a large number of homes. The gas is consumed in the burners and then converted into heat that is supplied to the home for keeping it warm. Broadly speaking, gas furnaces are of three types; single stage furnace, Two-stage furnace and a modulating furnace.

  1. The single stage furnace:

This type of furnace is a host to only one kind of operation- an easy on and off operation. These furnaces work with a gas valve that is opened and closed. The flow of gas occurs at one rate. The kind of furnace operates around eighty percent fuel utilization efficiency. The furnace lacks complete control and is not as efficient as the other modern-day options. The pro here is that the installation cost is very low.


  • Two-stage furnace:


The two-stage furnace can be controlled with two settings. Full speed and a half. Thus offers control on the temperature in your house and is a lot quieter. This system is capable of communicating with thermostats and can read the heating load of the home and adjust accordingly. The air does move at a slower pace, but this furnace provides the required comfort when winters are around.


  • Modulating furnace:


The modulating variable speed furnace can control the heat output and speed in coordination with the outside temperature and the comfort. This furnace can be controlled to the max just as wanted and is one of the most energy-efficient option available in the market. The furnace keeps the circulation of air continuous even when the process of heating is stopped. The furnace can cost a bit on the heavier side but can save a lot of money in the long run in form if energy costs. Modulating furnaces are a must have in very cold climates and can work fabulously to regulate the temperatures throughout.

The electric Furnaces on the other hand distribute warm air throughout the home evenly. These furnaces are laced up with 3-7 resistance coils and utilize the ductwork for air distribution. These furnaces are less economical and should be a resort when other options are not a fit. Oil furnaces have been one of the options as well, but the fact that they depend on the non-renewable source of energy make them a little less relevant.

How do furnaces work?

Heating furnaces are detailed systems wherein each component is integrated in a way that serves the purpose in most convenient and efficient way possible. The system works in conjunction to keep a house winter ready, and the process should be understood to know how to run and maintain a furnace for a long term.

In a typical furnace system, thermostats and a furnace are in the process of interaction. The thermostat constantly reads the temperature of the air and regulates it accordingly by sending a signal to the furnace that further decreases on increases the heat quotient. The two main types of furnaces discussed above viz; gas and electric furnace work through this mechanism. In a typical setting, the thermostats send a signal, and the furnace adjusts the temperature of the air and keeping it going through the duct system.

In case of an elaborate setup, the furnace system might as well come in additional components besides the thermostats and the furnace. The temperature to be regulated may require one or all of the additional components to keep the process efficient and in control. A humidifier is one of such components that forms a part of the system and is used to regulate the humidity inside the home. This, in turn, increases the quality of air and makes the space comfortable.

The humidifiers may also prevent wooden products, that form a part of your living space, from warping or cracking. Another special component is the central air conditioner. The conditioners help cooling down the temperature of the indoor air just in the case the temperatures rise above what is comfortable. One of the additional components of the system is the air filter. Many furnace systems include an air filter to improve the overall quality of indoor air.

The process that gets the modern furnace working starts with the thermostat receiving a signal. Many furnaces give notice of the signal being sent by making a clicking sound. This is when the fuel is supplied to the burner for a controlled flame. When the burners are lit, the furnaces carry on an internal check to make sure that are the burners are working, and in case of a problem with any of the burner, the entire system is shut down for a brief period before an attempted re-ignition process.

When the burners start working, a heat exchanger device starts working by warming the air. This air is pushed forward only when the exchanger reached the operating temperature. This is the stage when blower motor starts working by circulating the air throughout the home via the network of ducts.

Modern-day furnaces are much more efficient and simple to use than what existed the long time ago. The maintenance of these furnaces is easier when the process is known, and the components are identified. The know-how protects from a failure and ensures that the safety mechanism stays in place. With continuous innovations, the fuel efficiency of these furnaces has reached up to a ninety-eight percent. The control has become easier, and the furnaces with sensors make it easy to live in a home that is constantly being monitored for warmth and comfort.

Identify the type of furnace in your home

To know how your furnace works and how to keep maintaining it, it is mandatory to know what kind of system is a part of your home. There are different ways to categorize the type of heating furnace. The major three categories include distinguishing in the basis of system type, for example, hot water, forced air, etc., on the basis if fuel type and on the basis of heat distribution. The heat distribution part is visible to the eye, and this can help to identify the type without having to go too thorough.

Identify the type of furnace categorized on the basis of physical appearances is:

  • Hydraulic radiators: if your system involves functioning on hot water, this is your furnace. The fuel used in these furnaces include oil, gas or electricity and involves a series of hot water piping throughout the house. The heat is distributed through hot water or steam which is admitted via a valve, and this warm air keeps the air within the house at the optimum favorable temperature
  • Electric Furnaces: These kinds of furnaces will involve the use of high current voltage in association with the heater coils and related elements. This furnace may involve having a propane tank as well. Electric furnaces can be recognized on the basis of the supply and the bills it generates.
  • Gas Furnace: the gas furnace has a visible flame while in operation. You can also identify this kind of furnace if you have a pipeline moving towards the origin of the furnace.

Identify the type of furnace on the basis of fuel:

  • Gas furnace: This furnace will require a supply of bottled gas or a pipeline of natural gas to keep functioning.
  • Electric system: This is when your furnace needs electric baseboards to circulate hot air throughout the space.

There are a lot of other ways that can help to identify the type of furnace used. For example The space from where the warm air flows in, your ducts, the process of heat distribution. In case of the metal radiator furnaces, copper tubing, wall convectors can help you recognize this type. Many such things are required to be noted to exactly conclude what type of furnace is being used.

A knowledge of the type of furnace being used can make you confident about the maintenance issues if any and you might be able to save yourself the trouble in case of any problem. The technicians tend to hype the bill in case you lack the knowledge.

Being aware will save some costs as well. Furnaces have been an integral part of our houses, especially during winters. With the cost efficiency and many more improvements being made on the part of the functionality, it is easier to have one around. It is also recommended to go for some research before deciding on which one to use. Look for the option that is most suitable on the basis of energy available to you or the climate you live in.