Which heating system is better for you and your home? To make the best choice, it is important to for you to understand the difference between a boiler and a furnace.

Understanding Furnaces and How They Work

A furnace uses air to generate heat that is circulated to various rooms in the home, which is called a forced-air heating system. It moves cool air through a heat exchanger, where the air is warmed. The heated air then travels through a HVAC ductwork system to be evenly dispersed throughout the house. Furnaces come in three variations: horizontal, upflow and downflow. They can be powered by oil, electricity, gas or propane. They are best suited for homes with ductwork and central air conditioning that need consistent heating over larger areas.

PROS AND CONS OF FURNACES

Advantages:

• Flexibility: Furnaces can use electricity, heating oil, natural gas and propane. Some of the latest models are even using solar or geothermal energy.
• Faster: It takes less time for a furnace to generate and circulate heat, allowing homes to warm up quicker.
• Lower Upfront Costs: Furnaces are less expensive to install. There are more types and models to choose from and the supply lowers the cost.
• Less Damage: When a furnace leaks, it leaks air, which decreases energy efficiency, but it doesn’t damage the home like a boiler leak can.
• Don’t Freeze: Furnaces can’t freeze like boiler pipes can in extreme low temperatures. Boiler pipes can freeze and burst since they use water for heating.

Disadvantages:

• Noisy: A furnace blower makes noise when it forces air into the ducts. Depending on the age, the sound can be loud.
• Inconsistent Heating: Heating with air is not consistent. Some rooms are more comfortable than others.
• More Expensive to Run: They require more fuel to produce heat.

Understanding Boilers and How They Work

Boilers circulate hot water or steam through radiators and radiant floor heating to heat your home. This type of heating system works well in homes that don’t have ductwork to distribute warm air, plus homes that already have a radiant heating system. In addition to the boiler, the system includes baseboards, radiators, a network of pipes and a circulator pump. These components are placed across various rooms and spaces to facilitate the even dispersion of heat. 

PROS AND CONS OF BOILERS

Advantages:

• Energy Efficient: Boilers typically require less fuel to generate heat, resulting in lower energy costs.
• Reduced Noise: They use steam from heated water rather than a blower from a forced-air system, leading to quieter operation than furnaces.
• Less Maintenance: Boilers do not have filters that require cleaning and have fewer moving parts.
• Consistent Heat: Heating from water or vapor is more consistent than the heat produced by forced air and distributes the air more evenly since the heat doesn’t go through ducts or a vent.

Disadvantages:

• Heat Exclusive: Boilers only provide heating and don’t have cooling capabilities. While a furnace can’t cool the air, the ductwork from the system can be used for central air conditioning.
• Higher Upfront Costs: Due to a complex installation, they can be expensive to install because they take more time and effort.
• Risk of Leaks: Old or damaged boilers have a higher risk of water leakage, which can lead to future water damage.
• More Expensive to Run: They require more fuel to produce heat.
• Slower Heat Adjustment: Boilers require a longer transition period to adapt to thermostat temperature changes.

What are the Differences Between a Furnace and a Boiler?

The biggest difference between a furnace and a boiler is how the systems operate. A boiler heats liquid inside a tank and then pushes the heated water through the pipe system that is installed throughout the building or residence. The pipes generate heat to warm areas of the home. A boiler system will keep the areas warm if it’s able to heat water and generate steam. A furnace system uses a heat exchanger to heat air that is pushed through ductwork and vents to warm up different rooms. It uses a blower motor to push and circulate the heated air.

Efficiency and Energy Costs

Heating air consumes more energy than heating water, which is why furnaces use more fuel over a shorter timeframe than boilers. Concerning expenses, boilers often come with a higher initial cost but are more durable than furnaces. How well the unit is maintained is also a huge factor.

Your boiler vs. furnace monthly cost partly depends on the cost of fuel and partly on the heating efficiency of your system. Newer systems are dramatically more efficient than older models, with new boilers being more efficient and less expensive to operate than new furnace systems. If you’re installing a new model, both will attain and maintain at least 95 percent energy efficiency if they’re properly maintained.

Older furnaces or boilers have an energy-efficiency AFUE measurement around 56-70 percent. Today’s systems have an efficiency rating that is as high as 98.5 percent. In new and highly efficient systems, practically all the energy they consume goes directly toward heating your home. Look for units with an ENERGY STAR^® rating.

Upgrading your furnace or boiler to one with an AFUE in the 90 percent+ range can cut your heating bill almost in half. You can reduce your carbon dioxide emissions by that much or more, depending on the fuel your system uses.

Maintenance, Costs and Lifespan

Maintenance is an important factor for keeping both systems in good shape. Boiler maintenance requires an annual inspection by a certified technician. It is recommended to flush the boiler, lubricate the pumps twice a year and to check for leaks every month. Furnaces also require an annual inspection and cleaning. Your technician will check carbon monoxide levels, gas lines, flame sensors and more. And every one to three months, the filter should be changed.

Most boiler problems will require you to call an HVAC professional because the parts are complex but there is little to no maintenance required. Common problems are leaks, emissions issues and temperature problems. Furnaces are better suited for do-it-yourself repairs and furnace maintenance like resetting your circuit breaker, replacing a clogged filter or installing a new safety switch.

A well-maintained boiler can last between 10 and 25 years, depending on the type, usage and regular maintenance schedule. With general wear and tear, you may notice water leaks, longer heat times and odd noises that indicate part failure. Electric furnaces can last 20 to 30 years, and gas furnaces can last 20 to 25 years. Toward the end of its lifespan, you may notice signs to replace or repair your furnace, including uneven heating or cooling, high carbon monoxide levels and loud rattling.

Choosing the Best Option

Understanding the difference between boiler and furnace systems is crucial in maintaining a comfortable indoor atmosphere. While both provide warmth, the systems rely on different methods. A furnace primarily heats and circulates the air through your home, ensuring each room stays warm. A boiler heats water to provide heat and hot water for daily needs like showers and dishwashing.

Choosing between a boiler and a furnace often comes down to the building’s age and your personal preference. Older homes might benefit more from boiler systems, while newly constructed homes usually contain furnaces. The goal is to ensure comfort and warmth, regardless of the season.

To make the best decision for your heating needs, consult a local Lennox Pro to help you determine your home's most efficient and effective heating solution.

This has been reviewed by Lee Butler, Senior Product Marketing Manager, for accuracy. Lee brings 12 years of expertise in the HVAC space.