At the heart of a radiated heating system is the boiler. For radiated systems, it produces and moves hot water to the radiators which distributes warmth throughout the home. When the boiler heats up the water, the temperature rises to the point where it is boiling. As the water turns to vapor, it spreads throughout the heating system, warming the pipes and radiators along the way. To heat up the water, the system has to burn fuel.

High efficiency boilers get their name from the fact that when they burn the fuel, more of the heat produced helps heat the water. In other systems, a larger portion of the heat is lost during the process, but with high efficiency boilers, the heat is more efficiently used to heat the water and turn it into vapor.

Because efficient heating is critical during the colder months, finding the right boiler for your home’s needs is important. The right boiler can keep energy bills reasonable and your home comfortable. This guide will explain what to look for in a high-efficiency boiler and what brands are reputable.

How is boiler efficiency measured?

The Annual Fuel Utilization Efficiency (AFUE) ratings of boilers usually fall between 80 – 96%. This number represents the estimated percentage of fuel converted into heat for the home. Typically, the higher the percentage, the higher the price tag of the unit. The standard AFUE rating is 80 – 84%. High-efficiency boilers usually have an AFUE rating of 90% and higher. Finding a high-efficiency boiler is easier once you understand the value of the AFUE rating.

British Thermal Units (BTU) are a measurement of the heat produced. It represents the amount of energy required to raise one pound of water one degree Fahrenheit. For heating, the higher the number of BTUs, the more heat produced by the unit.

High efficiency boiler brands

Noritz   Indoor Residential Condensing Natural Gas Combination Boiler

  • AFUE rating: 95%,
  • Heat rating of 120,000 BTUs
  • Fuel type: Natural gas
  • Unit price: $2,027.98

This boiler features an integrated Grundfos pump, which helps maximize the flow rate. Because the water is flowing at a more constant rate, it is able to get to the rest of the system before losing too much heat, making this an extremely efficient natural gas boiler.

Noritz   Indoor Residential Condensing Propane Combination Boiler

  • AFUE rating: 95%
  • Heat rating of 120,000 BTUs
  • Fuel type: Liquid propane
  • Unit price: $2,260.13

This propane boiler has a flow control feature that helps move the hot water more efficiently, regardless of the season. The more efficiently the water flows through the system, the more consistently, evenly and efficiently it can produce heat.

Westinghouse   Natural Gas Space Heating Wall Mount Boiler

  • AFUE rating of 96%
  • Heat rating of 140,000 BTUs
  • Fuel type: Natural gas
  • Unit price: $2,431.52

This boiler features a five-to-one turndown ratio that helps the appliance choose the proper energy usage needed to meet demand. It’s one of the most efficient boilers available and is ENERGY STAR rated.

Westinghouse – Liquid Propane Space Heating Wall Mount Boiler

  • AFUE rating: 95.1%
  • Heat rating of 199,000 BTUs
  • Fuel type: Liquid propane
  • Unit price: $2,316.84

This Westinghouse high-efficiency boiler can heat and circulate 9.88 gallons per minute while raising the temperature 35 degrees. This helps it get the water to its optimal heating temperature faster.

Rinnai – M-Series 90,000BTU Natural Gas Boiler

  • AFUE rating: 95%
  • Heat rating of 90,000 BTUs
  • Fuel type: Natural gas
  • Unit price: $2,586.35

Rinnai’s M-Series 90,000 BTU combi boiler comes with a copper-nickel integrated heat exchanger. The composition of the heat exchanger helps transfer the heat from the metal components to the water more efficiently.

Rinnai – M-Series 120,000BTU Natural Gas Boiler

  • AFUE rating: 95%
  • Heat rating of 120,000BTU
  • Fuel type: Natural gas
  • Unit price: $2,657.85

This boiler has a modulating pump, which helps move the heated water at a pace that gets it into your heating system before it loses too much heat. This way, the water is at the optimal temperature to heat your home as it enters the heating components.

Benefits of a high efficiency boiler

Having a high-efficiency boiler means that energy is recovered from the flue gases. The heat exchanger is specially designed to retrieve heat from fuel it burns instead of simply passing it out through the flue. It can extract over 90% of the heat that would have otherwise been discarded.

In the past, water would circulate a central heating system. The water would pass over a flame until the desired temperature was reached and then the water would begin the journey around the circuit. The problem with this design is that there was a lot of heat energy wasted. The water passed over the flame for such a brief period of time, much of the heat produced went into the surrounding atmosphere and was not focused efficiently to only heat the water.

A condensing boiler reroutes the return water to the secondary condenser. The secondary condenser is located just before the wasted hot air enters the atmosphere so the water that passes through now has another chance to warm up before reentering the boiler. By the time the water enters the burner, it has already been pre-heated so it takes less energy, or fuel, to reheat it to the desired temperature. This design saves homeowners in heating costs overall and helps them use less energy each month.

High efficiency boiler costs

Price of the unit

Typically, a high efficiency boiler will cost between $2,000 and $3,000. A high efficiency boiler with an AFUE rating of 95% and a heat rating of 60,000 BTUs costs between $2,300.00 and $2,500.00. When the heat rating is increased to 150,000 to 160,000 BTUs, the price increases to $2,650.00 to $2,850.00.


Installation can cost between $2,500 and $5,000 for most gas boilers. An oil-fired boiler typically costs between $3,000 and $6,500 to install.

Maintenance and repairs

The cost to maintain your boiler will largely depend on the type you have because the costs of parts can vary greatly. On average, however, you can expect to pay between $250 and $350 to repair your boiler. Replacing damaged or aging ductwork will cost around $35 to $55 per linear foot, and that includes labor and materials.

Cost savings

A new high efficiency boiler can pay for itself in energy cost savings. Compared with a less efficient 82% AFUE boiler, a 90% AFUE boiler can save you $69 per year while a 97% AFUE boiler can save you $113 per year. That represents a lifetime cost savings of $1,389 for a 90% AFUE rated boiler and $2,265 for a 97% AFUE rated boiler.

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