Replacing a Furnace? 3 Things to Think About Before You Do
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Replacing a Furnace? 3 Things to Think About Before You Do


If the furnace in your Portland area home is near the end of its useful life, decisions about furnace replacement may be weighing on you. Here are three aspects to consider when replacing a furnace.


To make up for inherent inefficiency, older furnaces are often larger than necessary. Simply replacing a furnace by matching the size of a 15- to 20-year-old furnace with a modern unit will waste money and natural resources. While your old unit may only have 65 percent Annual Fuel Utilization Efficiency (AFUE), modern condensing gas furnaces can achieve up to 98 percent AFUE.

Your trustworthy HVAC contractor will carefully measure your home’s interior volume and ductwork, and then use the Air Conditioning Contractors of America’s Manual J to calculate correct size for the new model. If a contractor offers some “rule of thumb,” or shows you calculations from the back of an envelope, find a different contractor.


While you may have had limited choices 30 years ago in selecting the old furnace, today’s models can use natural gas, electricity, propane or fuel oil. Consider variations in fuel costs and supply when replacing a furnace. Some fuels unavailable even 10 years ago in the Portland area may be cost-effective and better for the environment than mainstream sources:

  • wood pellets
  • biomass
  • waste motor oil
  • biodiesel

On the other hand, natural gas is relatively inexpensive today, due to ramped-up domestic deep-shale drilling, and most homes are already set up with gas lines and venting for a natural gas furnace. This is probably why natural gas remains the most popular furnace fuel.


A new furnace is a major investment. While you want to keep your family warm and safe through many heating seasons, you may hesitate over the expense. You can roughly calculate how long a new model will need to be in service to recover its cost through fuel efficiency.

Compare it (assume 90 percent AFUE) to your old model (assume 65 percent AFUE); the new model will save you approximately 28 percent on fuel use. Assume your annual energy bill is $1,000; you will save $280 the first year and every year thereafter. If replacing a furnace may cost you $2,800, you will recover that installation expense in 10 years through fuel savings.

For additional help and resources with replacing a furnace in your Portland area home, please contact us at Roth Heating & Cooling.

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