What is a boiler system? How does it compare with other residential heat system types? When should you choose a boiler system for heating your home?
Since you’re here, you likely have some knowledge of boilers, but these are the kinds of questions answered in this Central Boiler Buying Guide for homeowners and business owners. This is the place to research:
- Boiler Basics & How Heat is Distributed
- Boiler Types
- How Boilers Compare to Furnaces and Heat Pumps
- Top Boiler Brands
- Prices for Boilers and Installation
- How to Size a Boiler System for your Home
- A Note About Efficiency
Boiler Basics & How Heat is Distributed
Here’s how a boiler works. The boiler’s burner consumes fuel to create heated combustion gasses. They pass through a heat exchanger that transfers heat into the water before being exhausted from the house. The hot water is circulated through a closed system of pipes to baseboard radiators or through radiant heat floor tubing. The heat from the water radiates into the living space. The water cools as it circulates, eventually reaching the boiler where it is reheated.
Controls regulate when the burner fires and maintain the temperature of the system’s water. The increase in volume of heated water is accommodated by an expansion tank.
- Heat distribution: Most boilers circulate the water to baseboard radiators or in-floor radiant heat systems using a pump/circulator. The radiators have fins like a car radiator that maximize surface area for efficient transfer of heat.
- Boiler size: The heating capacity of a boiler is measured in Btu’s of heat it can produce in one hour (Btu/h). However, to simplify the numbers, the heat capacity is typically listed in MBH where M=1,000, B=Btu, and H=hour. Residential boilers are produced in capacities from about 35,000 Btu/h to 399,000Btu/h, so written as 35 MBH to 399 MBH. Each model is made in several sizes. See more information below on sizing a boiler to your home or light commercial needs.
- Boiler efficiency: Boiler efficiency is measured in Annualized Fuel Utilization Efficiency (AFUE) and expressed as a percentage of the heat created being transferred into the system’s water rather than lost in the combustion gases exhaust. The least efficient boilers have AFUE ratings in the low-80s. The most efficient have AFUE ratings above 95%.
- Whole-house heating: When your thermostat calls for heat, it triggers the boiler’s circulator to begin pumping heated water through the system.
- Zoned heating: One of the compelling reasons to consider a boiler system is that it allows for zoned heating. When a zone is being heated, control valves allow the right amount of hot water to enter the zone’s radiator to deliver the desired heat. If space is not being heated, the control valve remains closed, and the hot water bypasses the radiator.
- Fuels: Natural gas is the fuel most used, but boilers can be designed to heat with propane, heating oil, biodiesel fuel and wood.
There are several considerations when researching boilers. Here they are with a brief overview:
Standard (non-condensing) boilers vs. condensing boilers:
Boilers with AFUE efficiency between about 80% and 84% are termed standard efficiency. If the units have 85% to 90% efficiency, some brands call them high-efficiency boilers. Most standard boilers have cast iron heat exchangers. These are the most affordable boilers, and they meet federal minimum efficiency standards. Condensing boilers can be floor mounted (large capacity) or wall mounted (small-medium capacity) units. What sets them apart is their efficiency levels of 95% AFUE or higher. The efficiency is achieved with a complex heat exchanger, usually aluminum or stainless steel, that maximizes heat transfer through condensing the moisture that is a byproduct of combustion.
Water boilers vs. steam boilers:
Water boilers create water temperatures that do not exceed 200F. Steam boilers heat the water to the boiling point and then push steam through the system to deliver heat. Steam boilers are the minority of boilers made. Both can be fired by a range of fuels.
Floor standing vs. wall mounted boilers:
Boilers have traditionally been installed on the floor, and many still are due to size and weight. These units are also called floor mounted or free-standing boilers. There are floor standing boilers for all fuel types, and all boilers fueled by oil, biodiesel or wood are installed on the ground. Some gas-fueled floor mount boilers can be optionally mounted on the wall.
Wall-mounted boilers are space-saving, gas-fueled boilers. Most boast efficiencies of 90% AFUE or higher. As such, they can be vented through the wall rather than through the roof. Brands like Rinnai that make tankless water heaters also produce wall-mount boilers because of the similarities in design and function between the two types of equipment. Most of these units deliver less than 200 MBH and have aluminum or stainless steel heat exchangers.
Staged and modulating boilers:
These are usually high-efficiency or condensing boilers. They operate either in several capacities such as low, medium and high or in a modulating spectrum of capacities that rise and fall by just a few percentage points. The benefit of staged and modulating boilers is that they deliver more precise heating that enhances indoor comfort and energy efficiency.
The name is short for combination boilers and means that these units heat your home and meet your hot water needs too, eliminating the need for a separate water heater. The separate functions are called “space heating” and “water heating.” The water sent to your taps is separated from the water that flows through your heat pipes. Combi boilers are attractive because they save space, and most offer excellent efficiency.
How Boilers Compare to Furnaces and Heat Pumps
Boilers are one of three popular heat sources for homes and commercial spaces. Here’s an overview of how they compare in essentials.
- Gas and oil furnaces: Furnaces deliver heat through ductwork and grates in rooms or zones. Natural gas furnaces can be modified for propane. Oil furnaces only use home heating oil. Furnaces are an excellent choice in any climate and for homes that already have ductwork. These heaters last 15-20 years depending on their quality. Furnaces are the most affordable of the three with prices starting at less than $600 (unit only). Our Gas Furnace Price Guide has in-depth information on brands, features and prices.
- Heat pumps: These units deliver both heating and cooling. They are powered by electricity. Heat pumps use a compressor to circulate refrigerant between heat exchanger coils, one outdoors in the condensing unit and one indoors in the furnace or air handler. The result is the movement of heat from inside to outside in the summer and the reverse in the winter. Heat pumps last about 20 years when properly installed and maintained. A heat pump is a good choice for hot-to-cool climates. They become ineffective when outside temperatures are sub-freezing. Heat pump prices start at about $1,200(unit only). See our Heat Pump Guide for additional information.
- Boilers: These units are ideal for new construction and for replacing an old boiler. The cost of installing piping and radiators is prohibitive in buildings already outfitted with ductwork. Heat pumps and boilers cost more than furnaces, and boilers last 20-30 years, the most durable of the three. Boilers don’t operate using forced air like the other two, so they are quiet and don’t spread dust, other allergens or odors throughout the space they heat. Boiler systems with radiant floor heating create a very comfortable home in winter, and boilers are suitable for all climates. Boiler prices start at about $1,300(unit only).
Top Boiler Brands
There are more than 100 brands of boilers, but here is a list of the top brands. All the best boiler brands are excellent in quality. The difference in the durability and performance of any boiler system is the quality of the installation, so hiring an experienced contractor to install your boiler and set up the system is essential.
- Bradford White
- US Boiler
Each of these brands makes condensing units that are Energy Star qualified.
Other brands that make high-quality, efficient boilers are Buderus (by Bosch), Burnham (by US Boiler), Carrier/Bryant, ECR International (by Dunkirk), ECR, Energy Kinetics, IBC Technologies, Navien, NTI, Olsen, Rinna, Utica and Viessmann.
Prices for Boilers and Installation
How much does a residential boiler cost? That’s what we’ll answer here with a look at residential boiler prices and installation costs.
Standard Gas Boiler Prices: These are non-condensing gas boilers with efficiencies from 80% to about 90%. Their size range is about 35 MBH to 200 MBH. Most are fed by a natural gas supply from the local utility company. Propane is delivered to the home and stored in tanks rented from the supplier. Rental is typically free if the customer uses a minimum number of gallons of propane annually.
- Standard gas boiler prices: $1,225 to $2,900
Condensing Gas Boiler Prices: These 90%+ efficiency models range in size to 399 MBH, and their large capacity accounts for part of their much higher cost.
- Condensing gas boiler prices: $2,700-$7,500
Oil Boiler Prices: Oil boilers are only used in the Northeast US and Eastern Canada due to a lack of natural gas and propane in those regions. Most are non-condensing boilers.
- Oil boiler prices: $1,700-$6,800
Combi Boiler Prices: As we noted, combination boilers heat space and water in separate pipe systems to deliver 2-for-1 performance. Combi boilers range in size to about 150 MBH.
- Combi boiler prices: $1,900-$4,500
Boiler Installation: Having your boiler properly installed ensures that it runs as efficiently and durably as it should. Installation includes materials and supplies required to install the boiler and hook it up to an existing pipe and radiant heat or radiator system.
- Boiler installation: $1,200-$2,200
How to Size a Boiler System for your Home
It’s impossible to over-emphasize the importance of having a boiler sized correctly for the space it will serve. Most contractors will conduct a traditional Manual-J Load Calculation to determine heat loss through the various aspects of your home’s construction such as windows, doors, walls and the ceiling.
We’ve prepared an in-depth guide for sizing any HVAC equipment properly with a Manual-J load calculation, but here is a quick and easy way to have a ballpark idea of what boiler size you’ll need. It starts with finding your zone on this US Climate Zone Map below.
Now, use this chart based on climate zone and the size of your home to estimate the size of the boiler you’ll need. The ranges are based on variables such as how much insulation your home has, its number of and the energy efficiency of doors and windows, roofing material, the foundation type and whether your home or building is a single-story or multi-story structure.
- Zones 1 & 2 (hot): 18-30 Btu/sq. ft.
- Zone 3 (warm): 25-35 Btu/sq. ft.
- Zone 4 (moderate): 28-40 Btu/sq. ft.
- Zone 5 (cool): 40-50 Btu/sq. ft.
- Zone 6 (cold): 50-60 Btu/sq. ft.
- Zone 7 (very cold): 50-60 Btu/sq. ft.
There are several points to take from the data above and other considerations:
- The colder your region is, the larger the boiler capacity will need to be to meet your home’s heating requirements. For example, a 2,000 square foot home in Zone 7 would require a boiler capacity of 100,000 to 120,000 Btu or 100-120 MBH. The same home in Zone 4 would need a boiler with 56-80 MBH capacity and in Zone 1 would need a boiler capacity of 36-60 MBH.
- If you’re replacing a boiler, it will need to be smaller than the old one if the home has newer windows or more insulation than when the previous boiler was installed.
- A replacement boiler will need to be larger if it will be required to heat additional space such as a finished basement or converted garage. Large additions require a separate boiler or other sources of heat.
A Note About Efficiency
Boiler costs relative to efficiency look like this:
- Standard boilers, 80%-84% AFUE: Lowest cost
- High-efficiency standard boilers, 85%-90% AFUE: Moderate cost
- Condensing boilers: 90%-98% AFUE: Highest cost
If eco-friendly heating is a high priority for you or if you plan to live in your current home for at least seven years, then a high-efficiency standard model or a condensing boiler makes sense.
When you want a cost-effective boiler for your climate, these are your top options:
- Zones 1-3: Standard boilers
- Zones 4 & 5: High-efficiency standard boilers
- Zones 6 & 7: Condensing boilers
Thank you for using our guide for researching your boiler options. If you have comments, questions or are willing to share how much you paid for your boiler system, please join the conversation. And if this has been helpful, please share it with friends and followers to assist them in researching a boiler and comparing boilers with furnaces and heat pumps.