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High Efficiency Boilers

Updated Oct 31, 2016
By Chris Brooks and Gary Sprague

Boilers provide heat by distributing heated water or steam through radiators or radiant floor systems. High efficiency boilers are relatively new to the marketplace, and for many homeowners they are a welcome change. If you’ve ever wondered why your old boiler ran all day and it seemed the fuel truck was parked in your driveway every week, it’s because many older boilers had efficiency ratings of 50-70%. This means that only 50-70% of the fuel you purchased was used to heat the house while the rest, 30-50%, was wasted up the chimney and elsewhere.

High efficiency boilers, which have an annual fuel utilization efficiency (AFUE) of 90% and above, use condensing technology. These boilers work by recovering heat from the flue gases that simply exit a house from the flue of a conventional non-condensing boiler. They condense the water vapor from those gases and recover heat that would otherwise be lost. One indication of the extra heat extracted is that the gases coming out of the flue in a condensing boiler have a temperature of 50-60° F as compared to the 120° or more in a non-condensing boiler.

Which Boilers are High-Efficiency?

Here is a short list of high-efficiency boilers. All burn natural gas, with the exception of those that explicitly state "oil-fired".

This is not a comprehensive list -- there are many high-efficiency boilers that we have not included.

How Efficiency is Measured

The measure of a boiler's efficiency is its AFUE. AFUE is the ratio of annual heat output of a boiler (or furnace) compared to the total annual fuel energy consumed by a furnace or boiler. For example, a boiler with an AFUE of 90% means that 90% of the energy in the fuel becomes heat for the home and the other 10% escapes up the chimney and elsewhere.

The current standard for residential boilers, included in the Energy Independence and Security Act of 2007, requires a minimum efficiency of 82% for gas-fired boilers and 84% for oil-fired boilers manufactured after September 1, 2012. In January 2016, the Department of Energy (DOE) adopted new standards for boilers, raising minimum efficiency levels to 84% for gas-fired boilers and 86% for oil-fired boilers. These new standards take effect in 2021 and will result in consumer savings of $.35-1.2 billion over 30 years, according to DOE estimates.

The Energy Star Program, run by the U.S. Environmental Protection Agency and Department of Energy, awards an Energy Star label to boilers that have an AFUE of 87% or greater for oil boilers and 90% or greater for gas boilers. There are now several boilers on the market that claim an AFUE of 97%.

Boiler efficiency has a direct impact on your energy bill. The more efficient your boiler, the less fuel you use, which results in lower bills. A boiler's maximum efficiency is reached when it operates at full load.

Benefits and Drawbacks of a High Efficiency Boiler

The main benefit of a high efficiency boiler is it can give immediate savings on fuel costs, possibly reducing your bill by as much as half. These units are also better for the environment, with far lower emissions. Another benefit of a high efficiency boiler is that it does not require a traditional chimney; instead, it uses a short PVC pipe inserted through the side of the house.

One drawback of condensing boilers is their higher upfront cost. The purchase price is higher, sometimes double the cost of a standard, mid-efficiency unit. One way to determine whether the higher cost is justified is to calculate the payback period. Elsewhere we provide detailed instructions and examples on how to calculate the payback period, but in short, the payback period is the time taken to recover an investment. You can think of it as the ratio of investment to annual savings.

For example, if a new high-efficiency boiler costs $10,000 to install and saves $2,500 per year in fuel costs, the payback period will be four years. But when estimating payback period, one must also consider maintenance and repair costs. Because a high efficiency boiler has more complicated computers and circuit boards, they are more likely to have problems and require servicing. Not only are these boilers more likely to need repairs, but repair costs are much higher with these units, often double the cost to repair a mid-efficiency boiler. So when you combine the higher purchase price with higher maintenance and service costs, the payback period of a high efficiency boiler is usually over 10 years, and often between 10-15 years.

Should You Buy a High Efficiency Boiler?

The answer to this question varies from homeowner to homeowner. Here are some issues to consider:

  • Are you willing to pay a premium to reduce your home's impact on the environment?
  • How confident are you in your installing contractor's skills? A poor installation is the cause of many service calls.
  • Assuming that your contractor does a good job on the installation, how long is your payback period?
  • How long do you plan to own your home? Is that longer than the payback period of the boiler?

Many buyers place a high value on upgrading their home's appliances to be as environmentally friendly as possible. If you are not price-sensitive, then a high-efficiency boiler is a great choice. Just be sure that you're confident in your contractor's skills.

If you are price-sensitive, than a high efficiency boiler can still be a great choice: replacing a low-efficiency boiler with a high-efficiency condensing boiler could help you save up to 30% on your heating bills. However, in this situation, it's important that you calculate the payback period to make sure that you'll see the benefit of your investmetn. And, it's critcal that you vet your contractor thoroughly: because high-efficiency units are more complicated than mid-efficiency units, there's more that can go wrong. And, if your contractor makes a mistake, you'll more than likely bear the cost of that mistake for years to come.

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