Boiler vs Furnace Explained

Boiler vs Furnace Explained: What’s the Difference?

You’ll be surprised that many people who have had boilers or furnaces in their homes for years do not know or understand them.

It is very easy to confuse the difference between the two devices as they both look the same, require similar maintenance and services, use the same power supply, have the same components, and provide us with the same services. However, the important thing for you to keep in mind is to understand how each heating system works so that you can make an informed decision when it’s time to choose your home’s heating system.

When it comes to differentiating between the furnace and the boiler, the first thing you should never forget is the furnace heats the air that is distributed through the house, and the boiler uses hot water to distribute heat through the house. Although the furnace and the boiler work to achieve the same goal of providing us with adequate heat, they both operate in different ways.

A furnace uses the burners to heat air that is distributed to your house via a blower and the home’s duct system. It runs on natural gas or electricity. The boiler uses hot water to heat your home and then distribute heat to hot water radiators, baseboard heaters, or radiant flooring systems through small water pipes. And it can run on gas, oil, electricity, or alternative fuels.

If you’re one of the many people who have had questions about the difference between the two devices, this article will have the differences between Boiler vs Furnace Explained and look at everything you need to know and understand about the furnace and the boiler. It provides detailed explanations and instructions on maintenance, installation, and troubleshooting.

Heat Efficiency (Furnace and Boiler)

When it comes to heating efficiency, the age of your furnace or boiler is the first factor that matters. The energy efficiency of a boiler or a furnace is measured by annual fuel utilization efficiency (AFUE).

If a boiler or furnace has an AFUE value of 60, it can only convert 60% of the fuel to heat. The remaining 40% goes to waste. So, your Furnace or Boiler is only able to save energy according to the AFUE value. A system with an AUFE value of 56% – 70% is considered low efficient, 80% to 83% is medium, and 90% to 98.5% is high.

The energy efficiency values for older furnaces or boilers range from 56%-70%. Meanwhile, modern systems can be as high as 98.5%. In comparing the AFUE values of a boiler and a furnace; gas and oil-powered furnaces have an AFUE of 78%. A high-efficiency furnace model is 85% and higher.

A steam boiler running on oil has an AFUE of 82% and above. Gas boilers have 80% and higher. Then hot water boilers that run on oil have an AFUE of 84% and above.

When comparing AFUE ranges, keep in mind whether or not the heating system has a pilot light. A continuous pilot light, for example, is less energy efficient than either no pilot light or a system that condenses flue gases in a second heat exchanger, which is more efficient. Seal combustion is also seen in the most energy-efficient heating systems.

Which Provides the Most Comfort?

When we think about heating comfort, we typically expect a steady supply of warmth evenly distributed around the house or hot water, either on-demand or whenever we want it. We are all vulnerable to severe weather, it is essential for you and your loved ones, especially the elderly and children, to maintain a stable indoor temperature. The Furnace and the Boiler are the two major devices that help achieve this; therefore, it would be beneficial to understand what they can and cannot do.

Here’s a table that compares the comfort and convenience of a boiler against a furnace.













The Boiler distributes heat throughout the room evenly.





Depending on the position of the ducts, it fluctuates






A Boiler’s temperature constancy is considerably superior to that of any Furnace. They circulate heat throughout our home, ensuring that there are no cold spots.




The temperature consistency of a furnace depends on what type of Furnace you have; there may be cold spots in different parts of the house.







One of the benefits of using a boiler is that it has no sound. Because they produce hot water instead of air, boilers are usually quieter than furnaces.




The Furnace can be very noisy depending on the quality of your Furnace. Because of the continuous operation of the fan blower to push air out to your home, the constant flow of air through the duct, and the constant burning of the gas, the Furnace is never completely silent.




The air in your is normal and safe because, unlike the Furnace, the Boiler has no business with it.



If the Furnace ever has any dirt in like dust, it could contaminate the air and cause allergic reactions. The continuous in and out movement of air in your home can make it very dry, and you will need a humidifier.











Dust and other allergies may be trapped inside. Ducts must be cleaned, and filters must be changed on a regular basis to maintain good air quality.






Boilers have a 15 to 30-year life expectancy and can run on natural gas, propane, heating oil, or electricity, depending on the kind you choose. Some boilers may also run on biodiesel and other sustainable fuels.




Just like boilers, furnaces have a 15 to 30-year life expectancy and can run on natural gas, propane, heating oil, or electricity, depending on the kind you choose.




Buying, installing, and running a boiler is twice the price of a furnace.



The average price for a boiler ranges from $1500 and above. The average cost for a gas furnace ranges from $600 to $1000.




Completely safe



Hands or items may be stuck inside the vent, especially by a child.




Various heat zones can be established around the house to ensure equal heating





CONS Expensive to install, and it requires a low temperature to prevent pipes from freezing It can be very loud because of the blow fan.




Detailed Explanation (Furnace & Boiler)

The Furnace and the Boiler are among the oldest yet highly efficient heating systems we still use today. To help you understand and choose which heating system is the best for you, below are the detailed explanations of the two devices.

The Furnace

A furnace is a device used to heat the inside of the home by heating the air. Unlike the Boiler, it sucks in the cold air, heats it, and releases it as hot air into your home. The Furnace distributes the hot air through the vents in the floors, walls, or ceilings. It is most commonly used in newer homes because it’s generally less expensive than the Boiler, and it runs on electricity, natural gas, propane, or oil.

How Does a Furnace Work?

When learning how the furnace works, it is important to understand the sequence of operation of the furnace. Below are the steps on how the furnace operates.

The source of gas to the furnace is connected to a pipe entering your house from the outside. For the LPG furnace model, it is connected to an outdoor storage tank. For the natural gas furnace model, it is connected to an underground natural gas pipe network.

Here is the sequence of operation of the furnace:

  1. After gas enters your furnace from the storage tank or the local gas supply network, the burners are lit.
  2. Once the burners are lit, cold air enters the Furnace, where the burning gas warms it up within the heat exchanger.
  3. The exhaust pipe then pushes out the combustion air out of the furnace through the vent.
  4. The blower fan then directs the warm air from the burners into the various parts of your house, keeping it warm. The distribution of heat in your home depends on where the thermostat detects the need for heat.
  5. As long as the burners are lit, and the warm air is constantly distributed, the temperature of your house will increase gradually, and the cold air will be redirected to the furnace through the return duct to repeat the same cycle.

Types of Furnaces (By Fuel Types and Operation)

Gas, propane, electric, and oil burning are the four main types of furnaces.

They all required a heat exchanger or a chamber to warm up the air except the Electric Furnace, which exposes heated elements for warmth. Also, they all need the services of the thermostat. The thermostat informs the furnace when heat is required and when a set temperature is reached.

Gas Furnace

Natural gas furnaces are the most popular and commonly used of the furnace types. They operate on the constant burning of natural gas.

Natural gas travels via a burner, which ignites to produce hot combustion gas, and then it raises the temperature of the air, which is then circulated through the ducts by the blower fan.

Natural gas furnaces are very efficient at producing even heating, and they are inexpensive to operate due to the low cost of gas compared to other fuels. Newer gas furnaces may be up to 98 % efficient, but previous ones were only around 65 % efficient on average.

Types of Gas Furnaces

The two major category types of the Furnace operate differently, and they are:

  • Conventional Furnaces

Conventional furnaces are a type that has been around for a long time. They exhaust combustion gases up a chimney flue very quickly before they have a chance to cool and before moisture can condense out of them. Because of that, the heat exchanger fails to collect enough heat from the fuel.

  • Condensing Furnace

Condensing furnaces can absorb heat at a typical rate even after the combustion exhaust gases have been cooled and condensed.

Two heat exchangers are used to accomplish this. The primary heat exchanger handles the corrosive condensed exhaust gasses of water and carbon dioxide. In contrast, the secondary heat exchanger runs the corrosive condensed exhaust gasses of water and carbon dioxide.

Carbon dioxide turns into carbon acid when it decomposes. The heat in the exhaust gases is drained until the water vapor drips out of the heat exchanger of the furnace, and the flue gases leave through a plastic PVC pipe rather than a mortar or metal chimney.

Types of Gas Furnace by Burner and Blower Operation

The conventional and condensing furnaces are further divided into three major categories according to how the burner and the fan blower of your furnace operates. The operation of your heaters burner and fan blower is referred to as “stage.”

These stages are:

  • Single-stage furnaces

This gas furnace only has one heat adjustment setting with the highest heat output.

When the gas valve is open, it allows for a lot of heat (flow), and when the gas valve closes, there will be no heat flow. Meaning there is no medium heat flow.

Single-staged gas furnaces are the most common gas furnaces. Their AFUE value ranges from 80% to 85%.

It comes with an electric efficient multi-speed blower motor. Which is also known as a constant torque or ECM motor. This will help you save money on electricity.

  • Two-stage or dual-stage furnaces

Unlike the single-stage, this type of gas furnace comes with electronic control, which allows the burner and burner flame to be set to a high or low setting, relative to the amount of heat required. Their AFUE value can reach 96%.

Two-stage gas furnaces will have either an electrically efficient multi-speed blower motor, also known as a constant torque or ECM motor, or a variable speed ECM motor, which will help you save money on electricity. The variable-speed ECM motor aids in maintaining a more consistent temperature level in the furnace.

Modulating Furnaces

This type of furnace has a gas valve that allows for more heat output adjustments (high, medium, and low), unlike the single and two-stage furnaces.

Modulating furnaces run longer than most furnaces, allowing for an even distribution of heat.

The modulating furnace has an AFUE value of up to 98%.

It also comes with a variable speed ECM motor, which helps reduce the electric energy used in operating the Furnace, saving money on energy bills.

Propane Furnace

This type of furnace needs propane to operate. If natural gas is not available in your area, then a propane furnace is the next best choice for you. It is a byproduct of other oil and gas processes, and it is usually stored in propane tanks outside of the house.

Although they can be very efficient, they do not produce as much heat as oil compared to oil furnaces. This means that the furnace will need to burn more propane to produce enough heat for your home. The AFUE value of propane furnaces ranges from 90 to 98 %.

Electric Furnace

You can go with an electric-powered furnace if you don’t want to have a natural gas line coming into your house. The system uses electric heating elements to provide the heat that transfers to the air. Electric furnaces are typically less expensive to buy upfront. They are smaller than other furnaces, which makes them easy to fit into most spaces.

Although the electric furnace model is not expensive to purchase, your energy bills increase as it uses up a lot of electricity to operate. Electric furnaces, like oil furnaces, are not very efficient, but they may be the best option for you in some situations.

Oil Burning Furnace

Oil furnaces are generally not expensive and, with proper maintenance, may last nearly as long as gas furnaces. Oil prices, however, change a lot, which means that your fuel bills will always be unpredictable.

These furnaces need to be cleaned of soot and dust accumulation regularly to stay in excellent operating order. Also, they are not as efficient as gas furnaces. The AFUE values of the oil furnaces range from 80 to 90%.

The Boiler

A boiler, just like the furnace, provides us with our desired temperature by the distribution of heat.

Instead of heating the air like the furnace, a boiler heats fluid like water or glycol using a fuel source. It can also be used as your home’s water heater by providing hot water for everyday domestic use, such as the kitchen, bathrooms, and laundry.

A boiler does not need ductwork and can most often be found in older homes.

How Does a Boiler Work?

There are basically three pipes connected to the boiler from underneath it in a gas boiler heating system.

  • One of the pipes feeds gas into the boiler from the main gas supply, usually located outside of your home.
  • The other pipe, however, lets cold water into the boiler to be heated.
  • And the last pipe is where the hot water from the Boiler exits from, travels through, and around your home.

Here is the sequence of operation of a boiler:

  • The gas burners and the heat exchanger are the two primary components of the b The burners heat the fluid, and the heat exchanger transfers the heat from one medium to another.
  • When you turn on your heating, a gas valve opens, which releases gas from the main gas supply into the combustion chamber inside the Boiler. The combustion chamber is where the gas burns and then releases energy in heat, which transforms water into steam.
  • Next, the burners heat the heat exchanger, transferring the heat to the cold-water pipe.
  • Once the cold water has been heated, an electric pump is located inside the Boiler or right beside it. Then pumps the hot water into a network of pipes around your home, passing through all your hydronic heating system like the radiators, baseboard heaters, or radiant flooring systems. The hot water flows through all the radiators in your home, entering from one side and leaving through the other.
  • The water becomes cold after passing through all of the radiators. Therefore it is returned to the Boiler to be heated before being sent back. This cycle repeats for days with the same water until a skilled specialist removes it.
  • The Boiler produces waste gasses as it burns, which must be disposed of outside your home.

Types of Boilers

There are three main types of boilers you can install in your home, and they are:

Combi Boilers

This is called a combi boiler because it provides home heating and hot water from a single unit. It is mostly mounted on the wall, and it functions just like a regular boiler.


  • Highly Efficient – This is the right choice if you are looking for a high-energy efficient boiler. Because it can be used to heat your home and provide hot water simultaneously, it saves a lot on energy bills. It does a job of two for the price of one.
  • Portable Size – It can fit into small spaces and properties because of its compact size. Also, you do not have to make space for water tanks or a cylinder because combi boilers use the main heating system to heat water.
  • Convenient – The combi heater can always heat the water whenever you need it without having to wait around for hot water.


  • Limited Flow Rate – When two or more outlets are being used simultaneously, it reduces the water flow rate. If you have a large building with multiple bathrooms, a combi boiler might not be the right choice for you.
  • Dependent on high main water pressure – Combi boiler can only heat water supplied from the main’s water supply. A man is the source of public water supply through pipes or cable. If your main’s water pressure is low, the boiler will not function appropriately.

Heat Only (Regular Boilers)

A heat-only boiler, also known as a regular Boiler, is most suited for businesses like hotels or large homes with higher water demand and require multiple taps and showers to use hot water at the same time.

The heat-only Boiler has three major components, and they are:

  • The boiler itself;
  • A separate hot water storage cylinder; and,
  • Cold water storage tank.

Regular boilers function by delivering hot water to the central heating system, such as radiators, and then storing it in a hot water storage cylinder for future use. A cold-water tank supplies cold water to the boiler, which is filled by gravity.


  • Excellent choice for many users – It is the best choice for a home with multiple bathrooms and high demand for hot water.
  • Very good for low water pressure – If you have low water pressure, unlike the combi boiler, heat only boiler is a perfect choice.
  • Suitable for the older heating system – They are a good option for older heating systems that cannot handle the high pressure of a closed system since they don’t require high-pressure water from the mains.


  • Delayed Heating – Because some modern heating systems may not be compatible with a traditional boiler, you may have to wait a long time for the water to reach the desired temperature.
  • Complicated Installation – They take up more space and limit boiler installation options because they require a cistern tank. A cistern tank is a waterproof container used for storing water.

System Boiler

System boilers are an upgraded version of the heat-only or regular Boilers. They can provide hot water on demand and heating water for your radiators. The system boilers have a separate hot tank but without vents or ducts. Water is supplied from the mains, and it does not require a cold-water tank because all parts of the Boiler are internal. The two primary components of this device are the Boiler and a cylinder.


  • Highly Efficient – They are appropriate for houses with high hot water demands, just like heat-only boilers, because they include a big hot water storage cylinder.
  • Space Economical– They take up less room than a heat-only boiler because they have all of their components internalized and do not require a cold-water cistern. It also means that the installation site is more flexible.
  • No Potentials Leakages– Because system boilers do not require any components in the attic, you won’t have to worry about potential leaks or freezing during the winter.
  • Easy to Install– Installation of the System boiler is easy because all the components are internalized.


  • Not Suitable For low-pressure water– The pressure of the mains supply mostly determines the flow rate of hot water within the home. Therefore if it is low, the flow rate will be limited. As a result, they are not suitable for locations with low water pressure.
  • Not Suitable for Older Heating System– The Boiler may not be suitable for houses with older central heating systems because older systems tend not to tolerate high water pressures.
  • Difficult switching to combi boiler– Because system boilers require a hot water storage cylinder, you’ll need to find enough storage space if you’re switching to a combi boiler.

Installation and Replacement (Furnace and Boiler)

Tools Needed for Installation:

  1. Allen Keys– Used to tighten and unscrew hexagon-shaped screws and bolts.
  2. Blow Torch– A blow touch is used to check the pipe system joints and make sure they are properly sealed.
  3. Combi Drill– For drilling holes on the wall.
  4. Drain Down Hose– Used for draining the heating system before starting any maintenance and repair work.
  5. File Set– A file is used for smoothening a rough surface when you need to.
  6. Hacksaw– Used for cutting pipes, nuts, bolts, and screws.
  7. Needle Nose Plier– This is used to twist, cut, and shape materials when necessary.
  8. Open-Ended Spanner Set – Used to tighten, unscrew, and adjust the nuts, bolts, and screws properly.
  9. Pipe Cutter and Wrench– Used for cutting and tightening.

How to Install a Boiler – Step by Step

Although it is illegal in some states in the United States to install a boiler on your own, it may not be as difficult as you think. However, as a homeowner, you must conduct a thorough study to determine whether it is legal for you to install a gas boiler on your own. The process of installing a boiler includes Unpacking the Boiler, reassembling it, realigning it, connecting it to utilities (power sources), and then thoroughly testing it to see if it can achieve maximum operational production efficiency.

Step One

First, select the suitable location for your installation.

The installation floor must be level, and the Boiler should be located near water pipes, vents, electrical outlets, and gas pipes.

Step Two

Next, it is now time to connect the boiler’s pipes to the rest of the system.

First, straight into the boiler section, install a circular pump; then, install a riser pipe gasket at the other end of the pipe.

A gasket is a piece of material that is used to seal the gap between two surfaces, in this case, two pipes. It enables you to connect other pipes to the water supply in your home.

Connect every pipe that corresponds to all the areas in the house after adding the appropriate amount of pipe gasket. With a wrench, tighten the joints.

Step Three

After the right plumbing has been installed, you can now begin the fixing and setting of the return and supply pipes.

The circulation pump is where this can be performed, and it is usually located on the return side of the boiler, while the flow is measured on the supply side.

Tighten the nut with a wrench and connect the boiler to the hot water tank with precision fittings and copper pipes.

Step Four

Now, it is time to install the smoke or flue pipe, which is very important.

Smoke pipes or ducts are used to control ventilation.

It is recommended to connect the boiler to the smoke pipe or chimney with a sheet brass pipe. Drill some holes and secure them with a metal screw.

Step Five

Next step is installing the gas pipes.

If you are using a gas boiler, then you will need to connect the appropriate gas pipes for your Boiler.

For natural gas boilers, you will need to link a black threaded pipe to Boiler.

Check all joints and connections to make sure everything is in place.

Please check your manual for detailed steps and instructions on how to do this properly.

Step Six

Finally, turn on the boiler for testing.

When the boiler is turned on, open the water pipe and fill the boilers with water. The automatic feed valve is covered, so you don’t have to care about pressure.

This final step requires a specialized expert.

The expert will start the boiler correctly, check CO2 emissions (an important safety risk), and make the necessary adjustments. After that, your boiler will be ready for use.

Because the Furnace has complex components like electrical, ductwork, plumbing, and gas, it is a complicated task. If you must install on your own, a qualified HVAC professional’s expertise is required.

However, for your reference, the step-by-step instruction on how to install a furnace is below.

Step One

First, choose where you want to install your furnace.

Depending on the type of furnace and the plans you have for the space. All furnaces have different instructions for installation. As a result, each unit specifies the clearance and ventilation requirements.

Before you begin the installation process, clean the area of any dust or debris.

If you are installing the Furnace in the basement, make sure it’s on blocks. The blocks should be at least 4 inches above the ground to avoid flooding.

You might have to get some rubber isolation pads if your Furnace did not come with some.

Now unpack your new furnace, remove all the loose parts and instructions manual from it.

Step Two

Choose where your air duct and drain will run.

The return air duct can either be by the side or on the bottom of the unit. Some come pre-marked with the correct size opening it needs.

Next, choose which side of the furnace you want the condensate drain to run.

Then place your furnace into the position, just a little above the condense drain output.

Step Three

Now, connect the ducting system.

After positioning the furnace appropriately, connect it to your home’s ducting system.

Then seal the furnace connections to the ducting pipe with metal foil tape or a duct sealant.

Please do NOT use duct tape for this step because it will not last.

Step Four

Connect the vent pipes.

The vent pipes have two terminals; the intake and the exhaust pipe.

Connect them a little above or below the furnace unit. This allows any condensation to drain safely and effectively.

Step Five

Now, connect the gas supply.

Connect your gas supply to the furnace, make sure there are no leaks on all joints and connections.

Step Six

After you’re done with the gas supply, connect the electrical supply. Generally, there is two connection on a furnace; a low and line voltage.

Carefully connect the two lines from the electric supply to the furnace. You can check your instruction manual to see where they connect them and make sure it’s correct.

Step Seven

Finally, connect your condensate drain. Usually, there is a hose connected to the drain hole on the floor of your basement.

Check out our full guide on how to find the best propane hose extension.

Maintenance (Furnace and Boiler)

Furnace Maintenance Tips

Test Your Furnace

Before the beginning of every cold season, turn on your Furnace and let it run for a while.

This was it is easier to fix any faults you dictate, on time. Also, it is normal if your system has any musty or dusty smell the first few minutes they’re on.

Pilot Light

The pilot light is the first little burner that ignites whenever you turn your furnace.

It burns slowly and eventually heats the rest of the burners. Whenever you turn on your furnace, always check the pilot light for a blue. If it’s not blue, then it’s a sign of a problem.

Change the Filters

For better functions, change your furnace filters at least once a year.

Keep Open Space

Always keep the area of the heating system open and clear. This will allows the functioning of your system to be more efficient.

Keep objects like furniture, drapes, toys, etc., away from the unit.

Boiler Maintenance Tips

Maintaining your boiler can be a little complicated. This is because the configuration of every component in it is different.

Generally, you can do some of the following activities on your own.

Oil the Pump

Oil the pump of your Boiler every now and then. This allows the system’s operation to be smooth. It also prevents the motor from overheating.

Clean the Pump

Always clean the pump of dirt and grime. This enables your Boiler’s heat transfer to be efficient.

Drain the Radiators

Draining the radiators will allow the flow of water to be steady. You do this by opening the valves to release the trapped air.

Temperature and Pressure

Don’t forget to check the temperature and pressure gauges. According to your result, maintain your Boiler’s proper water level.

Air and Water Level

Always check if your expansion tank has proper air and water.


Question: What is the cheapest form of heat?

Answer: Gas. Gas is always more efficient either with a boiler or a furnace.

Question: What is the cheapest system to install?

Answer: Electric systems. The electric boiler is the cheapest option, followed by the electric furnace.

Question: How much does it cost to replace a boiler?

Answer: Installing a new boiler costs $5,754 on average with a typical range between $3,645 and $8,162. A standard efficiency model (80%-89% AFUE) runs an average of $3,000 to $6,000. High efficiency models (90%+ AFUE) cost $6,000 to $11,000. Of that, labor costs $1,000 to $2,500.

Question: How long can a boiler last?

Answer: With a proper maintenance a boiler can last from 15 to 30 years.

Question: Is it ok to always leave the boiler on?

Answer: No! It can be tempting to always to leave the boiler on, however it is not advisable. The system should be allowed to rest, occasionally.  Overwork can shorten the life span of your boiler.

Question: Are boilers expensive to run?

Answer: Overall, yes. However, it will cost the same to run the throughout the winter for every heating system.

Question: Should I replace my old furnace?

Answer: Yes. Normally you’re advice to replace your furnace every 10years. But some furnaces can last longer than that in better condition.

Question: Is an furnace dangerous?

Answer: Yes it is. The biggest danger of an old furnace is carbon monoxide poisoning. The furnace grows weaker as it ages, along with its components. As they age, they start developing flaws such as gas leakages.  Carbon monoxide is an odorless and colorless gas that can cause nausea and dizziness. Overexposure to this gas is deadly.

Question: How much does a furnace cost?

Answer: The cost of a new furnace ranges from $1,500 to $6,500, depending on the model. The cost of installing a mid-efficiency furnace ranges between $1,500 and $2,500 on average. Mid-efficiency furnaces have an AFUE rating ranging from 80% to 89%.


The furnace and the boiler are one of the oldest heating systems we still use today. They play a major role in providing our homes with our desired temperature. Understanding what they are, how they work, and their maintenance will help keep them strong and long enough to provide us with the comfort we desire.

With proper care, both the furnace and the boiler can last as long as 30years. They are not the same, they work in different ways to get the same result. The furnace produces heat for the house by the heating the air. While the boiler does the same thing by boiling water and distributing the steams through radiators.


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