Furnace Sizing: You Can't Afford Not Making Sure It's Done Right
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Furnace Sizing: You Can’t Afford Not Making Sure It’s Done Right


If you’re ready for a furnace replacement for your Portland area home, consult an experienced HVAC contractor to make sure your new furnace is sized correctly. There is a common misconception that an over-sized furnace will get the job one. In fact, an over-sized furnace can cause a number of problems, including higher energy bills. Meanwhile, a furnace that’s too small will struggle to adequately heat your home on the coldest days.

Poorly sized furnaces can cost homeowners thousands of extra dollars in terms of energy waste and unnecessary repairs, as the result of extra wear and tear and short cycling. Proper furnace sizing is also important for maintaining consistent indoor temperatures throughout the winter months.

Professional furnace sizing is done using Manuals J and S. These guides, published by the Air Conditioning Contractors of America (ACCA), use a wide range of factors to help HVAC contractors select and install the most efficient furnace size for your home. You may also want to have the contractor inspect your duct system, and use Manual D to design a more efficient layout. The investment will pay itself back via energy savings within a matter or years.

An experienced contractor will want to inspect your home, attic and current HVAC system before making a sizing recommendation. During this inspection, he will be evaluating a wide range of factors that affect your furnace’s function, including:

  • The square footage of your home.
  • The number of windows and exterior doors, and their specifications.
  • Insulation in the exterior walls and attic. He will want to verify the R-value as well as the amount of existing insulation.
  • If you have a chimney, the contractor should take that into consideration as it’s another source of heat loss in the winter.
  • Heat generating appliances and lighting fixtures.
  • Occupancy. Bodies generate heat too, so the number of people living in the home can potentially alter the size of your furnace.

He will also ask you questions about your family’s desired indoor temperatures and whether or not some rooms tend to be hotter or cooler than others.

Is your Portland home ready for a new furnace? Please contact us for furnace sizing done right.

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