How much does it cost to install a natural gas boiler?

Reviewed by Adam Graham remodeling expert. Written by Fixr.com.

If you use steam or hot water to heat your home, you have a boiler doing the work. Gas boilers are one of the most common systems used for heating homes with hydronic or steam heat. Gas is common, cheaper than most fuels, and heats a home efficiently.

There are many different types of gas boilers, ranging in size, heating type, and material, which lead to a wide range of costs. The average cost range to install a gas boiler is $5,000 - $10,000, with most homeowners spending around $8,362 for a high-efficiency system for a new 100,000 BTU natural gas boiler with a standard gas pilot, installed.

Natural Gas Boiler Costs

Gas Boiler Costs by Material

The heat exchanger inside gas boilers is made with one of three different materials - cast iron, aluminum, or stainless steel. High-efficiency systems and newer wall-hung systems use stainless steel, which is lighter than the traditional cast iron and holds up better than iron or aluminum. Most boiler manufacturers do not make the material a selling point, so you may not know what the heat exchanger material is unless you purchase a very high-efficiency system. The material plays a small role in the boiler cost. Because each type is associated with other factors that also play a role in the boiler cost, there is a big difference in the cost for one versus another if you compare the same size and type. Each material has a range, which overlaps, due to the number of sizes and other features available:

Cast Iron Boiler

Cast iron is the oldest material used on heat exchangers. It is inexpensive, lasts a long time - up to 20 years - and handles temperature changes well. However, it is heavy and can only be floor mounted. It cannot be used in high-efficiency condensing systems and only has an efficiency rating of 80% to 88%. Costs range from $1,200 to $3,000, depending on size and other factors.

Aluminum Boiler

Aluminum is lighter than cast iron giving more options for mounting. It is more expensive than cast iron but less expensive than stainless steel. It also transfers heat better than cast iron but not as well as stainless steel does. It has energy-efficiency ratings up to 94% but cannot be used in condensing boilers. Costs range between $2,500 - $4,000 on average.

Stainless Steel Boiler

Stainless steel is the most expensive material for heat exchangers, but it is also the most efficient. It is used on wall-mounted units and has efficiency ratings up to 98%. It is used with newer condensing boilers because it resists the acidity of the condensing units better than cast iron or aluminum, but due to the acidity of these boilers, the heat exchanger can only be warrantied for about 7 years on average. Costs average from $3,000 to $8,000.

Hot Water vs Steam Boilers

There are two basic types of boilers - those that heat water to boiling and use the steam to heat homes and those that simply heat the water, which is circulated for heat.

Steam boilers are not as efficient as hot water boilers. They need to reach higher temperatures and use more energy. For this reason, it is less common to find newer homes and installations that use steam. It is more common to find steam radiators in older homes, which are the upright radiators installed beside walls.

Hot water boilers supply two types of heating systems - radiant in-floor heating and hot water radiators. In-floor radiant heating is one of the most efficient ways to heat a room. It circulates hot water through tubes in the floor, heating people and objects directly. Hot water radiators are long, baseboard-style radiators that are more efficient than old steam radiators and less expensive to run than electric baseboards.

Steam boilers, despite being lower in efficiency, have higher starting costs than water boilers. A steam boiler has costs starting at around $2,500 to $3,000, while hot water boilers start as low as $1,200 for standard-efficiency boilers.

Condensing vs Non-condensing Boilers

There are two basic methods of operation for gas boilers - non-condensing and condensing. Non-condensing boilers are also considered to be standard boilers. They vent only a percentage of the heat as exhaust because as much as 20% of the energy and heat they use and produce is lost during the venting process.

Condensing boilers trap the exhaust and condense it to retrieve some of the heat. This makes them more efficient, achieving up to 98% efficiency, while a standard boiler is from 80% to 94% efficient.

Non-condensing boilers are less expensive. They are also much lower in maintenance, and when made with cast iron, they are much longer-lasting. Condensing the exhaust raises the acidity level in the heat exchanger, so cast iron and aluminum would either corrode or be unable to handle the process. Stainless steel resists corroding for longer, but it lowers the boiler’s warranty. So while the boiler may last 15 years, it is only guaranteed for 7 on average.

Combi Boilers

Condensing boilers are so efficient that some people, who have smaller homes and use gas to heat their hot water, choose to use a single unit for both heat and hot water. This is known as a combi boiler, a type of condensing boiler that uses separate units to heat the water on demand for use and to circulate hot water for heating.

Combi boilers tend to be small, suitable for smaller homes, condos, and apartments. They save space and may be hung on a wall anywhere in the home. They have energy-efficiency ratings starting at 95%. The higher the efficiency and the larger the size, the higher the cost.

Combi boiler prices start at around $2,000 for very small units, with most having an average cost of about $3,000.

Sealed Combustion vs Non-sealed Combustion

Another factor in determining your boiler cost and efficiency is combustion. In standard combustion, it takes air from inside your home to start heating the water. Once heated, the exhaust is then vented to the outdoors.

In a sealed combustion boiler, outside air is brought in to start combustion before venting outdoors. This is more efficient because it does not take the heat from your home and vent to the outdoors. Boilers that have an efficiency rating of 90% or higher have a sealed combustion system. Sealed combustion boilers can be condensing or non-condensing and can be found in all three materials. Non-sealed combustion boilers tend to cost between $1,200 and $4,000, while sealed combustion ranges from $1,200 to $8,000 in costs.

Gas Boiler Costs by Brand

Like any appliance, there are variations in costs according to the brand you choose. Some brands specialize in high-efficiency boilers and have higher costs, while others make middle-of-the-road boilers with lower costs and longer dependability. Below is a list of some of the more popular boiler brands and their average costs.

What Size Gas Boiler Do I Need?

Gas boilers come in a range of sizes, based on how much heat or energy they produce. This energy is displayed in BTUs or British Thermal Units. The more BTUs a unit has, the more heat it produces.

It is important when using any boiler to get one properly sized for the space you are heating. Boilers that are too small struggle to heat the room, while boilers that are too large use more energy, costing you more each month.

BTUs for boilers are determined by multiplying the number of BTUs needed to heat one square foot of your home based on your climate zone, and the square feet of the space you are heating.

To find the size boiler you need, locate your climate zone by consulting the U.S. Department of Energy’s climate zone map. For boilers, the country is broken into 7 zones, with zone 1 being the lowest part of Florida (the Miami area) and zone 7 the very northernmost parts of Maine and Minnesota.

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To find your boiler size, calculate the square footage by measuring the length and width of the area you are heating, and multiply it by the BTUs for your zone. Below is the average boiler size to heat a space in zone 4 based on square footage:

Ideally, you want to be within 10% to 20% of this range. Do not go above 20% because this yields an oversized boiler that uses more energy than necessary to heat your home.

Labor Costs to Install a Gas Boiler

Installing a gas boiler is a complicated process that varies depending on the boiler type, where it is located, and condition of the pipes, vents, and drains or if they need to be added. It costs between $1,000 and $3,000 in labor fees to install a gas boiler, with most people paying around $1,600 for a straightforward installation. If you need a new exhaust vent, gas line hookup, or other work, the price increases with additional costs from $500 to as high as $5,000 for running a new pipe to the radiator or radiant floor heating system.

Gas Boiler Replacement Cost

The cost to replace a gas boiler is similar to the cost to install a new one. Most newer boilers are different from older models, especially those that are lighter and more energy-efficient, and require a new vent at a minimum. They may also require new gas lines, drains, and other work. The cost to replace a gas boiler and the cost to install a new one is roughly the same at an average of $8,362 for a high-efficiency unit in a 2,000sq.ft. home.

Cost to Run a Gas Boiler

To calculate the cost to run your gas boiler, find the cost of gas per therm in your area, the number of BTUs your boiler uses, and the number of hours you operate your boiler. The average cost of gas in the U.S. as of April 2020 is $1.028 per therm. 100,000 BTUs is equal to 1 therm.

Multiply the price per therm by the number of therms your boiler uses and the number of hours to get the cost to operate your boiler each day. To get the cost to run your gas boiler for one hour, multiply the number of therms it uses by the cost per therm.

A 100,000 BTU furnace uses 1 therm per hour, meaning running a gas boiler for one hour has an average cost in the U.S. of $1.028.

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Gas Boiler Maintenance

Boilers are not high-maintenance appliances, but they should be inspected yearly as part of their maintenance routine. During the inspection, the heat exchanger should be examined for signs of wear, the water pH tested, and any sediment flushed from the system. The heat exchanger is the part of the boiler most likely to wear out due to the acidity in high-efficiency units, so keep an eye on the pH and flush as necessary to help your system last longer.

Gas Boiler vs Gas Furnace

While gas boilers are a very efficient way to heat your home, many people also choose to use gas furnaces instead. The main difference is that a boiler heats water, which continuously circulates, while a gas furnace heats the air in the home.

Of the two, gas boilers tend to be more comfortable and efficient, particularly when used in conjunction with a radiant heat system. Gas furnaces tend to produce drier air, so they are less comfortable and less efficient. They rely on a system of ducts to circulate the air, while boilers rely on a series of pipes.

Due to easier installation, gas furnaces tend to be less expensive to purchase and install, with an average cost of around $6,000, compared to $8,362 for gas boilers.

Gas Boiler vs Heat Pump

If you are heating a small space or home or live in zones 1, 2, or 3, a heat pump is an efficient way to heat your home, while also offering cooling. Heat pumps take heat from the outdoors, so they are inefficient in very cold climates and for larger homes. Gas boilers are more efficient and effective, but they make less sense in warmer climates, which is why heat pumps are often installed there.

Gas vs Oil Boiler

While gas is the most common fuel for a boiler, oil boilers are available as well. This is a good option if you live in an area where a gas line does not run. Oil is more expensive than gas, but it burns hotter, so you use less of it to heat the boiler. Oil boilers are also higher in maintenance than gas boilers because oil produces more soot. They tend to be less efficient but have a similar cost range to gas.

Electric vs Gas Boiler

If you live in an area where gas is not an option and are heating a small home or home addition, an electric boiler is a good option for some homes. Electric boilers cost more to run, and while they are more efficient at converting energy to heat than gas, they are slower to heat. The boilers themselves are usually smaller, mostly due to the high costs involved with running them. An electric boiler is a good choice for additions in homes without gas heat because it is easier to put in a radiator or radiant floor heating using an electric boiler than it may cost to run ductwork.

Manual J Calculation

When you purchase a new heating system for your home, your HVAC contractor should perform the Manual J calculation to determine the correct size of the heating system for your home. The calculation takes into account the size of the area being heated, the amount of insulation, and the climate you live in. This is the most effective way of sizing a heater so that you do not end up with an oversized unit that wastes energy or an undersized unit that struggles to keep up with your heating needs.

Enhancements and Improvement Costs

Old Boiler Removal

Many HVAC professionals include the removal of an old boiler in the cost to install a new one. Others may charge a fee from $50 to $200 for this service, depending on the boiler age and type.

Boiler Insulation

One way to increase the efficiency of your boiler is to insulate it. Insulation for the exterior of the boiler has costs starting at $30.

Wall-mounted Gas Boiler

If you have a small or energy-efficient stainless steel boiler, it may be wall-mounted to save space. These boilers tend to be more expensive than others, with costs starting at around $4,000.

Programmable Thermostat

If you upgrade your heating system, you may want to upgrade your thermostat as well. A programmable thermostat saves energy by setting times for the boiler to be off when you are not typically at home. Programmable thermostats have a cost of around $145 - $230 installed.

Additional Considerations and Costs

• In many areas, you need a permit to install or modify any HVAC equipment, including having a boiler installed.
• It is always a good idea to increase your home’s energy efficiency before installing a new heat source. This includes insulating your pipes, upgrading your thermostat, or installing new insulation in walls.
• Installing your boiler inside your home rather than in an unheated area like the garage helps efficiency for heating your home because it does not have to work as hard.
• Natural gas boilers may be converted to run propane. Your HVAC technician makes this adjustment for you if needed.
• Boilers heat your home efficiently but do not cool it. If you want to add cooling to your home, add an air conditioner as well.