Improve Home Energy Use with an Efficient Furnace or Boiler


Efficiency Ratings are Only Part of the Story

Upgraded HVAC systems can offer potential energy saving opportunities in many homes. The transition from electric or heating oil or an older gas furnace to a high efficiency furnace can show savings of more than 25% in energy costs. But what do energy efficiency ratings for a new furnace or boiler really mean? And is there anything else to consider as part of a replacement project that can influence overall performance? Let’s see what we can find out.

Understanding the Efficiency Rating of Furnaces and Boilers

Furnaces and boilers have an efficiency rating called Annual Fuel Utilization Efficiency or AFUE. It is a measure of how efficiently the appliance converts energy in its fuel to heat over the course of a typical year. Specifically, AFUE is the ratio of annual heat output of the unit compared to the total annual fossil fuel energy consumed by a furnace or boiler. An AFUE of 90% means that 90% of the potential fuel energy becomes heat for the home and the other 10% is lost, usually up the chimney.

An electric furnace or boiler has no flue loss through a chimney and can have an AFUE between 95% and 100%.  However, despite their high efficiency, the higher operating cost of electricity make electric units a costly choice. If you are interested in electric heating, a consideration might be a heat pump system.

Replacing Your Furnace or Boiler

If you have an old, worn out, and inefficient furnace or boiler, the ideal choice is to replace it with a new modern high-efficiency model. If your house still has an furnace that was previously converted from coal over to gas or heating oil, it would be the best candidate for replacement.  Even those units that still have pilot lights rather than electric ignition, are candidates for replacement.

Before you purchase a new boiler or furnace, there are several items you could look into to make the most out of your new high efficiency unit.

  • On older homes you could have an Energy Audit done to benchmark how drafty the house is. There may be monetary incentives for investing in efficiency improvements throughout the home.
  • Consider insulation work that includes “Air Sealing”.
  • Don’t forget about insulation in crawl spaces and knee walls.
  • Insulate any ductwork that lives in non-conditioned spaces, such as attics and garages, with spray foam.

When shopping for high-efficiency furnaces and boilers, look for the ENERGY STAR® label. In our cold, continental climate, it makes sense to invest in the highest-efficiency system there is.

What About the Chimney

Properly functioning chimney systems will carry combustion byproducts out of the home. Therefore, chimney problems put you at risk of having these byproducts, such as carbon monoxide, spill into your home. Most older furnaces and boilers have naturally drafting chimneys. The combustion gases exit the home through the chimney using only their buoyancy combined with the chimney’s height. Naturally drafting chimneys often have problems exhausting the combustion gases because of chimney blockage, wind or pressures inside the home that overcome the buoyancy of the gases.

Newer, power vented units, expel the deadly gases out the side of the home through appropriate piping.  This creates a safer home environment for your family and pets.

Alternatively, many replacement units are direct vented out the side of homes which eliminates the need for a chimney all together.


Energy efficiency in replacement furnaces and boilers is a very important factor to consider before making a purchase. Additionally, there are other factors including insulation, ductwork, and venting that could be explored as part of a whole home energy retrofit.

For more information on from an expert furnace contractor in Madison, please visit our Contact Us page or call us at 608-233-1001.

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