As the cold breeze starts to whistle around, we close the windows, wrap ourselves with blankets, and turn up the thermostat to start the heater. If you live in a colder climate with freezing or near-freezing temperatures throughout the year, then a permanent and reliable heater is a basic necessity.
The two main heating systems in the U.S. are boilers and furnaces. But aren’t these two the same? No. A boiler and furnace are two completely different techniques/mechanisms that can heat a house. The reason for this confusion is people tend to use these terms interchangeably.
In this guide, we will take a closer look at the basics of both boilers and furnaces. We’ll compare them by how they work, their types, efficiency, cost, pros and cons, and more.
If you are a new homeowner looking to install a heating system for your house, then there is a good chance that you are considering either a furnace or a boiler. Heat pumps are becoming a good alternative nowadays but let us keep the discussion to the more “traditional” ways of heating a house.
What Is A Boiler?
Boilers are devices that supply hot water (or steam) for heating, processing, or powering something up. Let us focus on the heating aspects of the boiler. As the name suggests, a boiler is a device that heats a fluid (usually water) and distributes the hot water through a network of pipes throughout the home to radiators using special pumps. These radiators, including underfloor heating systems, cast iron radiators (on wall radiators), or baseboard radiators (in wall radiators), help in radiating the heat to keep us warm.
If the system uses only hot water for heat transfer and distribution, they are known as Hydronic Space Heating Systems. Alternatively, some boilers supply steam as well. Such systems are known as Steam Heating Systems.
The important thing about boilers is how they heat the water i.e., what kind of fuel they use. Common types of fuel for residential boiler systems are gas, oil, coal, electricity, and sometimes even wood pellets.
How A Boiler Works?
The working of a boiler is rather straightforward. When you set a temperature on the thermostat with the intention of heating up your home, the boiler unit starts doing its magic. We can divide the operation into two parts; heating the water and distributing the hot water.
Depending on the type of fuel a boiler uses, it first starts the combustion of fuel (in case of coal or oil), turns the burner on (in the case of gas), or passes electricity through a heating element (in case of an electric boiler). Regular water from a thermally insulated storage tank enters the main boiler unit and heat from burning of the fuel heats this water to very high temperatures.
Once the water temperature reaches a certain level, a special pump starts pushing the hot water through the pipes and when it reaches the radiators, you can feel the heat. As the water cools down in these radiator pipes, it circulates back to the tank and the cycle repeats until the thermostat feels the home is at your desired temperature. The boiler unit turns off once the set temperature is reached.
If the temperature of the water in the boiler gets just below its boiling point, then the system essentially supplies hot water. But if the temperature is high enough to completely vaporize the water, then the system supplies steam.
What Is A Furnace?
A furnace also helps in keeping you warm and cozy. But unlike a boiler, which radiates heat through hot water circulating around your home, a furnace heats up the air and blows hot air throughout the home with the help of a blower and a series of ducts and vents. So, a boiler uses thermal radiation from hot water to heat up the space while a furnace uses thermal convection by heating air.
As a furnace essentially works on air, it needs a blower that can help in circulating the hot air. Hence, such furnace-based heating systems are also known as forced-air heating systems. The older style of furnaces didn’t have a blower but worked purely using the power of gravity.
If the furnace uses ducts and vents for circulating hot air, we usually call it a Central Heating System. Does this mean there are ductless furnaces? Yes. Furnaces that work in smaller heating applications (for a small room or area) do not need any ducts or vents.
Another popular way to classify furnaces (apart from the usage of ducts) is based on the type of fuel used in the furnace. The most common types of fuel for furnaces are: gas, coal, oil, and electricity.
How Does A Furnace Work?
The main component of most modern forced-air furnaces is a heat exchanger. When you set the thermostat to heat your home, the heat exchanger kicks into action. If the furnace uses coal, oil, or gas as fuel, it will start the combustion process. In the case of an electric furnace, it starts the heating elements.
The blower sucks cool air, either from outside or from a special intake vent, and forces it through the heat exchanger. As the cool air passes through the combustion chamber or heating elements, it becomes hot. The forced hot air then goes through the main supply duct and is distributed in different rooms through vents.
Once the room or home temperature reaches the desired values, the furnace turns off its combustion process (shuts off the valve in case of a gas furnace). The cycle repeats as the temperature fluctuates.
Boiler vs. Furnace: Quick Comparison
| Feature | Boiler | Furnace |
| Operational Mechanism | Heats water to provide warmth via radiators or pipes | Heats air and distributes it through ducts |
| Heating Method | Radiant heating ensures even distribution of warmth | Forced air can heat rooms quickly but may be uneven |
| Noise Level | Generally quieter, as it doesn’t use blowers | Can be noisy due to the blower’s operation |
| Comfort | Provides consistent heat and maintains humidity | Can dry air, impacting comfort |
| Energy Efficiency | High with modern condensing boilers | Efficiency varies; higher with newer models |
| Fuel Source | Versatile: gas, oil, electricity | Primarily gas, but also available in oil and electric models |
| Indoor Air Quality | Better, as it doesn’t circulate dust and allergens | May worsen air quality by circulating airborne particles |
| Performance | Excellent in delivering consistent, even heat | Fast heating but may create hot and cold spots |
| Ductwork | Not required | Necessary, and can be a source of heat loss |
| Radiators | Requires radiators or in-floor piping | Not applicable |
| Water/Steam Piping | Essential for operation | Not required |
| Cost | Initially higher but potentially more efficient | Lower upfront cost but may be less efficient over time |
| Installation Cost | Generally higher due to complex piping | Typically lower, unless ductwork needs installation |
| Maintenance | Requires regular maintenance to ensure efficiency | Requires filter changes and duct cleaning |
| Durability | Long-lasting with proper maintenance | Life span varies, generally shorter than boilers |
Boiler vs. Furnace: Fuel Types And Energy Efficiency
The type of fuel your heating system uses affects its efficiency, cost, and impact on the environment. Although both boilers and furnaces work completely differently, they use similar kinds of fuel such as gas (natural gas or propane), electricity, coal, oil, and wood pellets. Natural gas boilers and furnaces are popular because they are cost-effective and widely available.
Energy efficiency in a heating system is the ratio of heat output to the fuel consumed (usually its caloric value). The Annual Fuel Utilization Efficiency (AFUE) is one of the standard ways to measure the efficiency of boilers and furnaces.
Generally, boilers (irrespective of the type of fuel) have higher efficiency than furnaces due to the simple fact that heating water is much simpler and easier than heating air. Another benefit of boilers is that water retains the heat for a much longer duration.
Electric heating systems, be it a boiler or a furnace, generally have significantly higher efficiency numbers (more than 90%). However, the cost of electricity in most parts of the U.S. has a major impact on the economic viability of such systems.
Both gas and oil-based heating units usually have efficiencies in the range of 70 to 80% while anthracite coal has about 60 to 75% of efficiency. Regular firewood is one of the least efficient fuels with efficiency ranging from 45 to 55%.
If your house already has a gas pipeline, then considering the efficiency and convenience, it seems like a logical choice to install either a gas boiler or a gas furnace.
Boiler vs. Furnace: Cost
Initial Cost And Installation
The fuel type and energy efficiency rating ultimately determine the cost of boilers and furnaces. If we look at electric boilers, they tend to be slightly cheaper than other boiler types. Hot water-type electric boilers typically cost between $800 and $6,000 while steam-type electric boilers are around $1,500 and $7,000. The typical price range of gas boilers is between $1,500 and above. Coming to oil boilers, their cost starts from $2,000 and goes all the way to $8,000.
Electric furnaces cost $1,700 to $15,000 while gas furnaces cost $2,000 to $9,000. On average, electric furnaces and ductless furnaces are slightly cheaper than their gas counterparts.
This is of course not including any installation. Installing both boilers and furnaces is labor-intensive and requires a professional touch. For a completely new setup, installing a boiler takes 2 to 4 days, depending on the size of the system. Typical tasks include setting up the boiler room, installing pipes, and connecting gas lines. As a result, the installation cost can be in the range of $1,000 to $3,000 for the entire unit.
Furnaces are much easier to install and typical installation takes a day at the maximum. Hence, furnace installation jobs are usually “hourly” jobs with a price range of $150 to $500 per hour.
Maintenance And Repairs
Boilers are much easier to maintain and need a professional inspection every year for a tune-up. Common maintenance jobs include checking for leaks, lubricating the pump(s), and flushing the tank.
As furnaces deal with air, the first and most frequent maintenance job is to check the quality of air filters and replace them if necessary (they can last 1 to 6 months, depending on usage). Furnaces also need annual check-ups from a professional for a system tune-up. Apart from this, a certified tech will look for carbon monoxide levels, leakage in gas/fuel lines and heat exchangers, inspect the vents, and more. There will also be cleaning and lubrication tasks as well.
If there are any repairs, then you definitely have to consult an HVAC professional due to the complexity of the systems. While there are fewer moving parts in a typical boiler (which means less chance of failure), issues such as leaks or emissions will cost between $200 to $800 to repair.
With a blower unit and other moving parts, furnaces are more prone to mechanical failures that require frequent repairs. However, the average repair cost of furnaces is slightly less in the range of $150 to $700.
Leaks in a furnace system mean problems with the ducts that leak air. While this does reduce the overall efficiency, it doesn’t have any major impact on the integrity of the house. But leaks in a boiler system mean water leakage. This can become an expensive repair and water in the floor or walls might cause damage to the structure of the house.
Boiler vs. Furnace: Other Differences
Heat Distribution And Heating Time
The heat distribution of boilers and furnaces dials down to the type of heat transfer they use and also the means to distribute the heat. Boilers radiate the heat with the help of radiators and heat people, surfaces, and objects. They tend to heat up the room/space evenly and uniformly. The heat in the room feels more consistent.
On the other hand, furnaces heat up air and force them through vents. If the circulation of the hot air is uneven, then the temperatures in a room will be uneven. Moreover, we know that hot air is lighter and has a tendency to rise up while cool air falls down. This also contributes to hot or cold zones.
Furnaces, especially electric furnaces can quickly heat a space as they are working directly on the air. But air tends to cool down quickly. So, the furnace must frequently turn on to reheat the space.
Boilers are quite slow to start radiating heat through radiators. But the benefit is the hot water stays hot/warm for a long time. This means the boiler doesn’t have to power cycle frequently. An additional benefit of a boiler is you can get hot water in your faucets.
Indoor Air Quality And Comfort
Furnaces heat air to keep the space warm. This dries the air in the room and also impacts the humidity of the room (as it removes moisture). Breathing dry air for continuous periods is really uncomfortable and it also has a negative effect on the life of furniture. When you combine this with the uneven heat distribution of furnaces, things can be uncomfortable, especially for those with respiratory issues or sensitive skin.
Another problem with furnace-based heating systems is airborne contaminants. As a furnace essentially blows air into the rooms, there is a good chance that it carries dust and other allergens through the vents. The blowing air from furnaces can also cause skin dryness, and irritating respiratory conditions. Adding humidifiers and HEPA filters can help, but they add extra costs. This is why regular inspection of air filters, ducts, and vents is necessary in case of a furnace heating setup.
Boilers generally don’t have these problems as they heat water instead of air. They even help in maintaining the humidity levels in the room/home, especially during winter. Radiant heat is much more comfortable to live in.
Noise
Both boilers and furnaces make noise while operating. But the only sound (that isn’t even guaranteed) is from the water circling through the radiator and pipes.
Furnaces deal with blowers and forced air that makes significant noise when circulating air through vents. The noise is even louder when the furnace starts. Older models or units that are not well-maintained can be even noisier, disturbing you, especially at night.
Space Requirements And Installation Complexity
Boilers are comparatively larger units than furnaces. They occupy a significant amount of space and that is why you’ll often come across “boiler rooms” when talking about them. If the system needs a separate hot water tank, then the space requirements become even bigger. Furnaces are somewhat better in this regard. They are “boxy” units and take up less space.
So, if you have a large house with more rooms that need heating, it is better to go with a boiler as it becomes cost-effective in the long run. However, for smaller houses or houses without a separate boiler room, furnaces are a much better choice.
If you are installing a completely new heating system in your house (that doesn’t have any existing piping or duct works), then installing a boiler system with its pipes and radiators is slightly less complex than laying out a new duct system.
That said, if your house already has the ductwork from the air conditioning setup, you can readily use that for integrating a new furnace for heating.
Lifespan
Boilers are durable and can last anywhere between 15 to 30 years or even more, thanks to their robust construction, closed-loop system help, and importantly fewer moving parts. Regular maintenance is essential, especially for leakages, and water quality issues like corrosion or sediment build-up.
Furnaces usually last 15 to 20 years, which is slightly shorter than boilers. You can extend a furnace’s life with regular maintenance, like replacing filters and keeping the ductwork clean.
Boiler vs. Furnace: Pros And Cons
Boiler
| Pros | Cons |
| Better overall efficiency as it involves heating water instead of air | Much complex installation |
| Heat is consistent and even | Higher initial cost (unit + installation) |
| Radiant heat is comfortable | Water leak repairs can be expensive |
| Makes less noise | Slow heating process |
| No issue of airborne contamination, dry air, or humidity loss | Needs large space |
| Maintenance is necessary by doesn’t cost much | |
| Suitable for large homes | |
| Lasts longer |
Furnace
| Pros | Cons |
| Can quickly start heating the room | Can dry air and heating might not be even |
| Lower initial cost | Noisy operation |
| Easy installation (without ductwork) | Regular maintenance (air filters must be changed frequently) |
| Duct leakages do not involve water | Risk of gas leaks |
| Suitable for small houses | Can result in spreading dust and allergens |
| No issues of freezing during winters | |
| Available in gas, oil, and electric models |
Which Heating System To Choose, Boiler Or Furnace?
There are several things that you need to factor in while deciding between a furnace and a boiler. First and foremost, if you are on a tight budget, a furnace seems like the practical choice. They have a lower initial cost, both in terms of the unit as well as installation. But keep in mind that it needs regular maintenance and frequent visits from an HVAC tech. While boilers tend to have higher initial costs, they are much more efficient in operation and require minimal maintenance. They seem economical in the long run.
Space is another big issue when choosing the heating system. Boilers need a lot of space. And if you have a large house with a lot of room to heat, boilers are a better choice. Small houses can get away with furnaces. If air quality and comfort are your priority, then there is no alternative to boilers.
Availability of fuel is also an important factor. While there are boilers that can run on different types of fuels, natural gas boilers are widely available and much more accessible. If your house already has a gas pipeline and you are willing to spend some money, then boilers are a worthy and economical option.
