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High Efficiency Boilers: What You Need to Know

July 15, 2013

What is a high efficiency boiler?

A high efficiency boiler, also known as a condensing boiler, is a water heater that’s able to achieve greater than 90% efficiency.  In the United States, the efficiency of a boiler is measured by annual fuel utilization efficiency (AFUE), which is a measure of how efficiently the appliance is converting the energy in the fuel into heat over the course of an average year.  New boilers are required to display their AFUE so that the consumer can compare across models.

In order to understand the benefits of having a high efficiency boiler, it’s important to know how it varies varies from a conventional boiler.

How does a conventional boiler work?

In a conventional boiler, fuel is burned and the hot gases produced are passed through a heat exchanger where a lot of the heat is transferred to water.  This process raises the temperature of water.  The required efficiency of a conventional boiler is about 70%-80%.

How does a high efficiency boiler work?

A high efficiency boiler works by recovering “waste heat” that usually exits a house from the flue of a conventional boiler.  It does this by condensing the water vapor that’s produced in the combustion process and using the heat from this condensation.

The manufacturers of condensing boilers claim that they can achieve up to 98% thermal efficiency, as compared to the 70%-80% efficiency that is achieved by conventional boilers.  The average condensing boiler has an efficiency of about 95%.

Update your boiler

Hopefully your boiler doesn’t look like this one…

What is the cost of installing a high efficiency boiler?

Condensing boilers are usually about 50% more expensive to buy and install than conventional boilers.  However, due to the decrease in fuel consumption that they allow, the extra cost of installing a condensing boiler is usually recovered in 2-5 years.  The payback period depends on the efficiency of both the original and the new boiler, the exact costs associated with installation, and how often the system is used.

There are many immediate savings associated with a high efficiency boiler.  Replacing an old boiler with a high efficiency boiler can give you savings of about 30% on your heating bills.  Additionally, in the United States there is a federal tax credit for the installation of condensing boilers, and some utility companies even provide additional rebates.

How can I tell if I need a high efficiency boiler?

It truly is up to your own discretion whether or not you need a high efficiency boiler.  Here are some pointers that we can offer:

  • If your boiler is older than 20 years, chances are that it would be a good investment to replace it with a high efficiency system.
  • If your boiler is 10-20 years old and you are experiencing high utility bills, then it is worthwhile to hire soemone experienced to help you evaluate your existing system.  In some instances, it’s more efficient to improve your insulation and ductwork than it is to replace your boiler.  In other instances, replacement does make sense.
  • Boilers can be retrofitted to increase their efficiency.  However, the costs of retrofits should be carefully weighed against the cost of a new boiler.

(Original Article)


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