Boiler Buying Guide
A quick guide to strategic product selection
Energy Source
Typically, you do not have much of a choice when it comes to choosing the energy source that will power your home's heating unit. This usually depends on the energy source available in your neighborhood: most commonly natural gas, propane, oil, or electricity. That being said, there are renewable energy source options to consider even if they may not seem readily available. These include but are not limited to sun, wind and geothermal.
► Click here to learn more about various heating system types. Learn how they work, what their advantages are, how cost-effective and energy-efficient they are, and what their environmental impacts are.
► View our Heating & Cooling or Heating Only Compare Technologies pages to see how different heating and cooling systems compare to one another in terms of efficiency, environmental impact, lifecycle cost and purchase price.
AFUE Rating
Boiler efficiency is measured using the Annual Fuel Utilization Efficiency (AFUE) rating. AFUE is the ratio of heat output compared to total energy consumed. In other words, AFUE measures how well a unit converts energy into heat for your home. An AFUE of 90% means that 90% of the energy in the fuel becomes heat and the other 10% escapes/is wasted. The AFUE rating does not include heat loss associated with the duct system or piping, which can be as much as 35%.
ENERGY STAR Label
Whether gas or oil, ENERGY STAR qualified boilers use about 6% less energy than a standard boiler. They:
- Have an AFUE rating of 85 or greater for oil and 90 or greater for gas
- Achieve greater efficiency with improved features, including:
- Electric ignition, which eliminates the need to have the pilot light burning all the time
- New combustion technologies that extract more heat from the same amount of fuel
- Sealed combustion that uses outside air to fuel the burner, reducing draft and improving safety
Proper size
Like with all HVAC equipment, the most common sizing mistake with boilers is in oversizing. This not only makes the new system more expensive to install, but also forces it to operate inefficiently, break down more often, and cost more to operate. Oversized heating equipment also can create uncomfortable and large temperature swings in the house.
It is your contractor's job to perform the correct sizing calculation for the building. Many contractors only check the "nameplate" (the label on the unit that has the Btu per hour output, among other things) of the existing system and then will try and sell you one just like it, or even worse, one that's larger. This is a not a correct sizing method and is not in your best interest.
Correctly sizing a heating (and cooling) system includes factoring-in the following:
- Local climate
- Size, shape, and orientation of the house
- Insulation levels
- Window area, location, and type
- Air infiltration rates
- Number and ages of occupants
- Occupant comfort preferences
To learn more about proper sizing, visit ENERGY STAR’s Central Air Conditioner Sizing Tutorial.
Control options
Ask your contractor about different controls that reduce the amount of heat lost through pipes during off-cycle periods or off-peak (warmer) days. Today there are many technologies available. Controls that modulate the boiler water temperature to reduce off-peak losses work better with condensing boilers. Ask about the cost of purchasing a boiler that has integrated controls compared to the cost of purchasing the controls as an add-on.
Indirect water heater
Modern boilers with low thermal mass and good insulation can actually make very efficient water heaters. When installing a replacement boiler, consider replacing your existing storage water heater with a well insulated indirect tank that connects to the boiler with an external loop. Even in the summer, you are likely to save energy because heat losses through the water heater flue will be eliminated.
Buy local
To reduce carbon emissions associated with product transportation and to support your local economy, we encourage you to buy your boiler from a local manufacturer.
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