- How a Furnace Works
- How a Boiler Works
- Changing Your Heating System Type: Good or Bad Idea?
- Boilers vs Furnaces: A Summary of Pros and Cons
- How to Choose Between a Furnace and a Boiler
- Compare Prices
If you’re building a home or addition, it makes sense to explore the two most popular heating options, gas furnaces and boilers. While both can adequately heat your home, there are differences to consider before deciding.
The differences between a boiler and a gas furnace are:
- Heat type: Boilers circulate hot water. The heat radiates out of pipes and radiators. Furnaces circulate heated air that flows through ducts and grates.
- Equipment cost: Boiler systems cost 35% to 65% more than gas furnace systems.
- Operating cost: Furnaces cost 0% to 25% more to operate.
- Central air conditioning: Furnaces support central ACs, boilers don’t.
- Indoor comfort: Boilers heat more comfortably because furnaces create drafts and dry out the air.
- Allergens: Furnaces potentially spread allergens such as mold spores and dust. Boilers don’t.
These differences and other important buying tips are discussed in this furnace vs boiler guide.
This table is a summary of the cost and most important features:
|Type||Unit Cost (1)||Infrastructure (2)||Fuel (3)||Efficiency||Zoning||DHW (4)||AC (5)|
|Furnace||$1,500-$5,200||$1,200 to $3,300||All||80%-98%||Yes||No||Optional/Integrated|
|Boiler||$2,300 to $8,000+||$1,800 to $6,000+||All||75%-96%||Yes||Optional||Separate|
(1): This is the installed cost of replacing just the furnace or boiler.
(2): This is additional cost for installation of the ductwork or piping/radiators.
(3): Gas is most common, but oil and electric furnaces and boilers are available.
(4): DHW is domestic hot water. Some boilers also heat water in your hot water tank
(5): A furnace works with central AC equipment to cool and distribute air. A boiler system does not.
How a Furnace Works
Most furnaces burn natural gas, propane or oil to heat the air in the combustion chamber. The furnace’s blower fan pulls cold air into the furnace where it is heated, and blows the warm air into the living spaces of your home. This is why these are called forced air systems.
The air circulates through ductwork. The ducts leading away from the furnace carry warm air and are called supply ducts. Those leading to the furnace carrying cool air are called return ducts.
Electric furnaces are an option. They are like large space heaters. Electric heat is the most expensive type. Electric furnace operating cost is three to five times higher than oil or gas heating, so they are only used in very warm climates where little heating is needed.
Zoning with any furnace type is accomplished with the use of dampers in ductwork leading to various sections of your home. They open to heat the zone and close to prevent the zone from being heated.
How a Boiler Works
Most boilers burn gas or oil to heat water. That’s why they are also called hydronic systems. Some heat water enough to turn it into steam. A pump circulates the water or steam through pipes. In general, the heat radiates out of the pipes into living space. Electric boilers are available but have the same disadvantage as electric furnaces – high energy costs.
You have options for dispersing the heat. Cast iron radiators were once the norm but are used less today. Baseboard radiators are more common.
Many homeowners think the most comfortable way to heat with a boiler is by running pipes beneath floor and allowing the heat to radiate up into the home. Warm floors in winter are wonderful beneath bare feet, and pets love them too.
Combination boilers are boilers that provide home heating and domestic hot water (DHW), the hot water that comes out of your taps. These are also called combi boilers. They don’t eliminate the need for a water tank, but they heat the water in it.
Tankless boilers are another option. Like tankless water heaters, they heat water on demand with natural gas or propane. Navien tankless boilers are a leading brand, but there are others to consider. Most are combination boilers.
A final option for those with a cheap supply of hardwood is an outdoor wood boiler.
Zoning of a boiler system is accomplished with valves that are adjusted to modify water flow to radiators, baseboard units and in-floor systems.
Learn more about boilers, options, top brands and prices in our complete Boiler Buying Guide.
Note: A boiler can also be used in a forced air system, known as a water to air system. A device called a plate exchanger is installed in the furnace. It is heated by the hot water, and air is circulated over it for heating. These systems are not common.
Changing Your Heating System Type: Good or Bad Idea?
Very few homeowners exchange one system for another due to the high cost. The cost is 35% 100% more than installing your preferred system during construction of the home or addition.
Single-story homes: Expect a change of systems to cost 35% to 100% more than a simple change-out of a furnace or boiler with the same type of equipment.
Multi-story homes: Ductwork or pipe must be installed in walls. This typically involves removing drywall and making additional modifications. Cost is 80% to 150% higher than simply replacing a boiler or furnace and hooking it up to existing piping or ductwork.
The high price doesn’t mean it can’t be done. Just consider the cost by getting several estimates for the work.
Furnace to boiler: This change is most often done in cool climates where AC is not essential. Homeowners do it because:
- They prefer the comfortable heat a boiler produces and/or
- They have allergies or other breathing issues that are made worse by forced air systems blowing allergens and dust around the home
Boiler to furnace: This change is typically made because the homeowner wishes to add central air conditioning. Future equipment and repair costs are lower with a furnace system too.
There are two parts to the system cost.
- The furnace or boiler: This is the unit that creates warm air (furnace) or hot water/steam (boiler).
- The infrastructure: Ductwork for furnaces or water-to-air boilers and pipes, radiators and/or baseboard units for standard boilers systems.
The table above shows both costs for each type unit.
- Furnace and ductwork systems start at less than $3,000 and rise to more than $8,000.
- Boiler and heat distribution system cost range is about $4,000 to almost $15,000.
The reason for the higher potential cost of a boiler system is that there are more installation options including in-floor hydronic systems that can be quite expensive.
Fuel costs are the cost to operate your system. New furnaces are either 80% efficient or 90% to more than 98% efficient.
Boilers range from the low 80s in efficiency to more than 95%.
Efficiency is the percentage of heat that is created that passes into the furnace ductwork or the boiler pipes. If a unit is 90% efficient, then 10% of the heat is wasted out the chimney.
The boiler advantage: A boiler costs less to run than a comparable furnace. For example, your energy costs for a 90% efficient boiler will probably be less than fuel costs for a 90% furnace.
Reasons: The first reason is that a water system retains heat longer than an air system, so the boiler fires up less often.
The second reason is leaking ducts in a furnace system lose heat. Most ductwork has small leaks where heated air escapes. According to the US Department of Energy and Energy Star, leaky ducts waste 20% to 30% of the heat traveling through them. That isn’t the case with pipes, especially when they are insulated where they run through unheated areas.
If you have a 90% furnace, it will burn up to 30% more fuel if your ductwork has leaks. To prevent heat loss, make sure your ducts are tightly fitted and taped. If they run through unheated areas like an attic, they should be insulated too.
System Add-ons Like AC
This is where a furnace has clear advantages over a boiler. Several components can be added to a forced air system that aren’t applicable to a traditional boiler system.
Air conditioning: Central air conditioning is easily integrated with a forced air system. An indoor coil is placed inside the furnace or adjoining it. Refrigerant in the coil collects heat in your home and carries it outside through a tube as warm air is circulated over it by the blower fan. The coil also condenses moisture and drains it away. The result is cooler, drier and therefore more comfortable air.
Boiler owners in warm climates often install ductless AC systems, also called mini split systems. We’ve prepared a Ductless Mini Split Guide loaded with information, pros and cons, costs and top brands of ductless systems.
Air Cleaners, Purifiers and UV germicidal lights: These components can be integrated with a forced air system, but must be separate systems when a boiler is used for heat (unless it is a water to air boiler system). Cleaners and purifiers include high-MERV media filters, PCO air purifiers and electronic air cleaners (EAC). They vary in their method of cleaning the air, their cost and effectiveness.
See our Air Purifier Guide for complete details and costs.
Climate Control and Comfort
Each system has its pros and cons when it comes to indoor climate control. Here’s an overview:
Furnace systems pros: The main climate control advantage is that central AC can be added, and when it is, you get the added benefit of dehumidification during humid summer days.
Cons: Cool air drafts. Furnace performance makes a difference. A single-stage furnace typically creates temperature fluctuations of two or three degrees. The air at the start and end of the cycle is often cool, and if you’re near a grate, it will feel drafty.
As you advance to a two-stage or variable-capacity furnace, temperature swings and cool air blasts are reduced.
These furnace types are explained in our Furnace Buying Guide. Click the Furnace tab at the top of the page to be taken there.
Boiler system pros: Since boilers use radiant heat, there isn’t any drafty air blowing around. Users find that to be a change they really like. There’s another climate control advantage – Boilers don’t dry out the air in your home during winter like furnaces do.
Cons: Besides not supporting central air, the other climate control concern about boilers is that they take longer to heat up if you’ve been away and have turned down the heat.
To solve this issue, homeowners often don’t turn down the thermostat when away during the day. A programmable thermostat or a WiFi thermostat will solve the issue too. When away for several days, a WiFi thermostat allows you to turn the heat up 3-5 hours before returning home to ensure your home is as warm as you want it to be when you arrive.
We’ve briefly discussed this issue. Our choice is a boiler system for those with severe allergies, asthma or other breathing trouble like COPD.
The reason is that forced air systems will spread dust and allergens into the air, even when a quality air filter is used. If there is mold in the ductwork and filtration is poor, it can be spread too, resulting in a critical health problem.
If you choose a furnace, explore the right air purification method for your needs in our Air Cleaner Guide linked to above.
With either a furnace or a boiler, regular dusting and vacuuming with a high-quality vacuum can remove many allergens and irritants from your home environment.
Boilers vs Furnaces: A Summary of Pros and Cons
Let’s summarize the advantages and disadvantages of both systems:
Furnace/forced air pros and cons
- Pros: Lower equipment cost and similar operating cost to boilers. Central AC can be easily added. Enhanced air filtration is possible.
- Cons: Temperature fluctuations and cool air drafts are possible. Airborne allergens and pollutants can be spread. Very dry air is produced in winter unless a humidifier is added to the system or a stand-alone humidifier is used.
Boiler system pros and cons
- Pros: Good efficiency, so operating costs can be controlled. Comfortable heating. Better for allergy and asthma sufferers. They don’t dry the air. Combination (combi) boilers heat water for domestic use.
- Cons: Higher equipment costs. Potentially higher repair costs. Possibility of leaking or freezing pipes. Need separate AC and air purification equipment. Heats up more slowly.
How to Choose Between a Furnace and a Boiler
Let’s look at the issue from several angles common to homeowners:
Budget: Furnace systems are definitely more budget friendly. You can get a furnace and AC split system with ductwork for about the cost of a boiler, pipes and baseboard radiators.
Comfort and breathing issues: Budget and climate issues aside, a boiler system offers more comfortable heating without the potential of spreading allergens or of making your home feel like a desert.
Where you live: If you want central AC because your summers are hot, then a ducted furnace system has its advantages when it comes to cost.
If cost isn’t a deciding factor and you want the comfortable heating of a boiler, here’s a popular solution. Install a boiler for whole-house heating and install a ductless AC system with indoor units where you most want the air conditioning.
Until you know exactly what each type of system will cost for your home, it might be hard to make a decision. Our service partner offers free quotes for all HVAC systems.
The estimates are provided by top heating and cooling contractors in your area. They are licensed and insured, and are pre-screened for experience and quality service. There is no obligation to take any of the estimates. The contractors can show you costs for the types of systems you’re considering, again, at no cost to you.
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