Furnaces 101 – What is a Furnace, How Does It Work and Why You Need It

Are you moving to a new place, a new home with central heating or domestic furnaces? Is this the first time you will be dealing with it? Well, that must be making you quite nervous and cautious. Rest assured knowing that central heating is quite safe, maintainable and affordable.

Moving to an extremely cold location or country for the first time can be quite a challenge, especially if one has been in a contrasting climate zone for most of their lives. Most people, both young and old, go through immense health issues due to this exact problem of adaptation. To overcome these problems, the human body needs to be gradually adjusted to the surrounding sub-zero temperatures.

A home furnace can prove considerably useful for this exact reason. However, first timers might find it difficult to understand how furnaces work. It is quite natural to have questions like – How do I choose a good furnace? What kind of furnace is convenient? How do I understand the functions of it? What kind of furnace can be worth my money?

But do not worry. We have compiled some easily comprehensible basic information about furnaces and their know-hows, just for you.

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The word furnace is a derivative of the Greek term fornax, meaning an oven. However, the furnace we are talking about does not refer to an oven, but the heating principle used in one.

A furnace is a device catering to all your heating and radiation purposes. Simply put a furnace helps raise the temperature of the substances and/or provide heat to the spaces subjected to it. A furnace may also refer to clay baking devices known as kilns.

In Europe, predominantly Britain, furnaces are industrial equipments used for extractions of metals or refining of fossil fuels. Its British reference is used for all industrial furnaces worldwide, except in America and Canada.

In North American countries like America and Canada, household heating systems or domestic radiators are called furnaces. These heating systems are homogenous distributors of heat in extremely cold weather conditions, using convectional heat produced by central furnaces, or as British call them – boilers, or heaters.

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Furnaces have been used for domestic central heating and ventilation since the ancient Roman and Greek eras. These furnaces ran on combustion of wood, gas and coal, which evolved into Central Hot Air Stoves during early 1800s. At the same time, steam based heating systems were proving to be a competition to hot sir systems.

Hydrologic central heaters, operated by boiling water, replaced most of these systems by late 18th century. With the invention of direct and alternating currents, electric furnaces were developed as an alternative to combustion central heating. Most of these types of systems are still available around the world. Although the above-mentioned heaters were used for large buildings, there are similar individual stoves and heaters offered for a single house.

Electric furnaces have been most preferable according to many families. Even though these furnaces are more expensive than a manual combustion stove, they are easy and safe to operate. The electric furnaces are available with three possible operations. However, one furnace cannot be run on multiple operations. Thus, it is important to check how your furnace works, and how compatible it is with the space you want to install it in.

  1. Single-stage furnaces

This type of furnaces are very primitive, and offer limited advantages. They work on two settings, and just need to be switched on and off as per your consumption. The furnace will supply heat to the room on full power, until the thermostat shows stabilized temperature. The furnace will then shut itself off.

These furnaces cannot be adjusted to give variable heat or ventilation. Hence, they give out the hottest blasts of air at the highest speed, giving temporary warmth. The cycle will repeat itself as soon as the thermostat shows low room temperature.

Such heating cycles provide uneven heat ventilation around the house. The single-stage furnaces are also known for their constant noise due to high velocity air distribution. If the winters in your locality are harsh enough to warrant using the furnace constantly, this type of furnace is not recommended as it consumes a lot of energy.

  1. Two-stage furnaces

The two-stage furnaces are a necessary upgrade to the disadvantages brought about by a single stage furnace. This type of furnaces overcomes the uneven heating cycles of a single-stage furnace, reducing the discomfort provided by constant fluctuation of warm and chilly room temperatures.

These furnaces can be adjusted to give out two speeds of even heat circulation: High (full burner power at 100% capacity) and low (reduced burner power at 60% capacity). The first lower stage operates smoothly at most climates. As soon as the temperatures gets extremely cold, the full power setting kicks in, providing excess heat. The rapid and uncomfortable heating provided by a single-stage furnace, is replaced by a slower and smarter heating cycle of a longer duration.

A two-stage furnace with a humidifier can allow better filtration of purified air throughout your house evenly. The noise created due to constant high power heating is reduced. Thus, a two-stage furnace beats a single-stage furnace in – even heat ventilation, air filtration, increased efficiency, and reduced energy consumption.

Thus, even if the two-stage furnaces have a higher cost in the market, compared to the single-stage furnace, they prove to be a better investment and an environment friendlier option.

  1. Modulating furnaces

If you do not mind expanding the budget for your domestic heating system, you can definitely consider buying a modulating furnace for your house. As the name suggests, these furnaces modulate the amount of heat supplied and the velocity of the air, which supplies it. It regulates the room temperature in accordance to the external weather conditions, and ventilates pure heated air evenly.

The heating takes place at regular increments of 0.5% by the rate of change of external temperature. The lowest stage in most modulating furnaces is 40%, and the highest is 100%. This allows the room to be consistently warm and comfortable. Even though the furnace is switched off, the motor allows constant circulation of pure air around the house.

Modulating furnaces are known to be 98% efficient, giving out majority of its energy input as heat. A good model of modulating furnace will cost you more than a single-stage or a two-stage furnace, thanks to its high efficiency and comforting performance. This smart furnace proves its worth for all your investment by saving energy and reducing combustion of fuel every time you use it. It is an excellent choice if you plan to settle in one house for more than 5 years.

With all these options, you can now easily choose the kind of furnace that fits your pocket and has the best compatibility with your living space.


Now that you know what furnaces are, and what types are available in the market, it is important to learn the basics of HOW it works. A furnace works in two steps: Heating and distribution of heat. The heat can be produced either by combustion of wood, gas or coal, or through electricity. The furnace then supplies this heat to the rooms of the building through an intermediary medium like water, steam or air.

A boiler is a furnace that distributes hot water throughout the taps of the house, and the generated steam is circulated around the rooms by steam. These boilers can provide double advantage through ventilation and plumbing. However, if it breaks down, both systems can cease to work.

Air convection has been proven a better and more efficient alternative to steam. The colder, denser air settles down near the furnace, which eventually heats up. This heated air becomes lighter and flows upward, through ducts and vents, to be finally released into the rooms.

The convectional currents keep the air circulating evenly throughout the building, no matter however many rooms need the supply of warm air. Warm air furnaces usually take help of a fan to circulate this air around, and reduce any case of stagnancy. The inbuilt air vents in older housing societies also assist the modern HVAC (Heating, Ventilation, and Air Conditioning) system of circulation.

Electric heating systems are less efficient and rarely used for large spaces. Thus, central heating systems work better on fossil fuel combustion.  Electric heating systems can prove useful for bungalows and villas. Nowadays, most buildings and bungalows use modern solar powered sources for central heating.


Winters in the Northern hemisphere, especially temperate, sub Polar and Polar regions can get fatally extreme. The sub-zero temperatures keep hitting record lows every year due to constant climate changes. If one is not used to such drastic temperature changes, it might even result in hypothermia. Hypothermia causes the decline of body temperature, that is, the body temperature falls below 95°F or 35°C.

Central heating or home furnaces have helped us control these extreme climates, with added health benefits provided to the young and the elderly alike. The winter mortality rates have decreased significantly since the economization of central heating. It also allows pure air to be filtered and circulated constantly, so that people do not have to sit cooped up in their houses with stagnant air.

A person moving to sub-polar region from a tropical country would definitely prefer a central heating system. It helps in maintaining your health and adjusting to the new lifestyle easily. At least your most important issue will not be lack of blankets of extra clothing.

Therefore, we can agree that extreme climate conditions and not being acclimatized to it warrants installation of a domestic furnace.


We saw how domestic furnaces are simple devices of space heating and ventilation. Although we say they are simple, are they really? How can your furnace be kept top notch throughout the winter, to keep getting comfortable warm blasts of air without any problems?

The internal mechanical structure of a furnace can be definitely far more complicated than we think it is. It is recommended to let professionals work on repairs and maintenance. However, some easy DIY steps can stop you from spending a couple of dollars over something as simple as filter replacement. You can find a step-by-step cleaning or replacement technique for furnace filter on the internet.

As most home furnaces filter then supply pure air around the house, the filter frame ends up accumulating a lot of dust. This dirt would have been easy to clean, had the moisture not allowed it to cake up. Dust accumulation also causes reduced efficiency, energy consumption and heating of the furnace itself. This calls for a replacement or thorough cleaning of the filter every year before the nippy weather of fall begins.

All furnace manufacturers and distributors recommend half-yearly or yearly maintenance of your furnace. Most manufacturers also recommend regular “tune-up” of the furnace. Now you might wonder what this tune-up exactly comprises of. The following points are just some of the things the technician will check and repair:

  • Blockage or leakage of the vent and drain systems are cleaned or replaced.
  • Combustion gases are analyzed to see if it fits the environmental guidelines or not.
  • Tightening the seal of the blower access door
  • Checking and cleaning of rusted/corroded parts of the furnace, like burners and electric wires. The burners should have proper ignition and flame.
  • The furnace’s blower wheel has to be removed entirely just for a checkup of dust and debris accumulation.

You might be tempted to think whether it is worth spending $80-$150 for your furnace’s annual maintenance. We suggest that you always call for professional help to get such a complex system fixed or repaired. In the end, it is the matter of personal safety, and safety and maintenance of your furnace. Thus, risking a lot more to save a hundred dollars would not be recommended.

The above mentioned issues can be solved by the homeowner if the person is also a heating contractor. Inexperienced homeowners or amateur technicians are suggested not to repair the system by themselves. Do not forget to take proper precautions when you undertake the task of cleaning simple things like the filter panel.


Sellers and cleaning companies usually provide a list of the furnace repairs and maintenance work. Checking the warranty in this case can reduce your repair costs by a lot. Make sure you do not change the contractors regularly, as improper maintenance can cause your warranty to become void.

So, are you now convinced about how furnaces can be a great and worthy investment? I hope this guide helped you with your doubts and questions. If you have any more of them, write to us and let us know!

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