Home Inspection Articles

Furnace Efficiency for Homeowners: Think like Home Inspectors

Posted by Olivia Hunt on Dec 20, 2012 3:30:00 PM

Furnace StickerIn recent years there has been quite an emphasis on the benefits “going green” and being energy efficient. As a professional Home Inspection company, we often get questions on furnace efficiency, what it means, and how having an energy efficient furnace can impact one’s home. During a Home Inspection our Home Inspectors will be able to tell you the age and capacity of the furnace, but if you want to be familiar with all the “efficiency” terminology, check out the information below.  

Furnace Efficiency Measurements

There are two efficiency measurements you need to be familiar with when dealing with furnaces: steady state and seasonal.

1)   Steady State Efficiency

Steady state efficiency refers to how much usable heat is created when a furnace is running. For example: conventional gas and oil furnaces have steady state efficiencies of roughly 80%. This means that when the furnace is on, 20% of the heat that is generated goes up the chimney and outside. The remaining 80% is transferred through a component called a heat exchanger, which then travels through the ductwork and ends up coming out of the registers you have in each room.

2)   Seasonal Efficiency

Seasonal efficiency is a bit more complex but refers to the off-cycle losses in addition to the steady state losses. You can think of it as an overall efficiency measurement.  Furnaces are not on all the time – not even in the dead of winter. They cycle on as the thermostat calls for heat, and cycle off again when the thermostat is satisfied. During the start-up and cool down, the furnace doesn’t operate as efficiently thus contributing to off-cycle losses.

In addition, when the furnace isn’t on, the heat from your house escapes up the chimney flue the same way that heat would escape from an unused fireplace, if the damper was left open. This  is also considered an off-cycle loss. If you add these off-cycle losses to the steady state losses you end up with the seasonal efficiency. Seasonal efficiencies for conventional gas and oil furnaces are about 60-65%.


What is the Difference Between Mid & High Efficiency Furnaces?

Mid Efficiency Furnace vs High Efficiency Furnace

  • Seasonal efficiency of about 80%
  • Achieved by minimizing off-cycle losses
  • Mid efficiency gas furnaces don’t have a continuously running pilot – it’s shut off when the furnace is idle
  • Some manufacturers install a motorized damper in the exhaust flue to close it during idle periods to prevent heat escaping up the chimney
  • Can be up to 95% efficient
  • Employs similar techniques to reduce off-cycle losses
  • Improves steady state efficiency – instead of having 1 heat exchanger, most have 2 or 3 that extract more heat from the burning fuel
  • More complex, and thus more expensive


Is a High Efficiency Furnace Right for You?

High efficiency furnaces are complex, and as a result they are often more expensive than conventional furnaces. High efficiency furnaces on average cost about $1000-$1500 more than a conventional furnace. That being said, if you were to spend $1000 heating your house with a conventional furnace, you can save close to $350 with a high efficiency furnace. Over time, these savings will pay for the system itself.

If you’re considering a high efficiency system on a retrofit basis, or as an option in a new home, it is best to speak to a reliable heating contractor to discuss the pros and cons of various models and the estimated increase in furnace maintenance costs. From there you will be able to determine what furnace is best for you.

Carson Dunlop clients are automatically enrolled in our not-for-profit Homeowners Association with access to group savings and discounts. Our Home Inspectors are available for consultation and provide technical advice for as long as the client owns their home. The Carson Dunlop Homeowners Association has a special relationship with Canadian Tire Home Services and AtlasCare to help clients save money and ensure they have the necessary heating system advice. The CDHA can save clients up to $1000 through our specialized relationships and partnerships. 

Topics: Home Inspection, Homeowners Association, Homeowner Tips