Signs of an Oversized Furnace
admin • December 7, 2011

Most people, when they choose a new furnace for their Wilsonville home, think that “bigger is better”. However, an oversized furnace can present just as many if not more problems than an undersized furnace. So, if you feel you may have overdone it in the past or you want to avoid making a mistake in the future, here are some signs that your furnace may be oversized.

Short Cycling

The most common sign of oversizing is short cycling. Short cycling occurs when your furnace turns on and off frequently because it reaches the thermostat setting so fast. Basically, your furnace is so powerful that it can produce what you need rapidly and then shuts off. But, because it does this, the temperature in your home is likely to cool much faster as well since the furnace isn’t on all the time.

Additionally, the on and off short cycling has a negative effect on your furnace, causing excess wear and tear on the system and eventually leading to extra repairs and in some cases early replacement.

High and Low Temperatures

When your furnace is turned on for a comfortable indoor temperature like 70 degrees F, the high and low temperature between cycles should be relatively close to that temperature. In an ideal situation, you shouldn’t even notice a fluctuation.

So, if the high temperature gets close to 75 degrees F and the low temperature is around 66 degrees F, you have a furnace much too large for the size of your home.

Furnace Room Issues

You might find that the space and exhaust given for the furnace are not sufficient either, especially if your previous furnace was replaced with this oversized unit. Backflow of a gas or oil smell or excess heat in and near your furnace room are both common signs that the furnace is much too large.

So, what should you do about your oversized furnace? If you have had that furnace for some time or just moved into a new home, it’s a good idea to have a new one installed. Have a proper load calculation done and then get a new furnace installed so you don’t have to worry about the system cycling on and off so often. If it’s a newer unit, call your heating technician and discuss possible options to reduce the negative effects of the miscalculation of its size.

The Clean Air Act technician testing air purity for indoor air quality in Portland, Oregon home.
By Rodger Brown January 24, 2026
Need indoor air quality improvement tips in Portland, OR, this winter? Learn how humidity control, better air filters, and ventilation can help you breathe cleaner air all season.
A woman relaxing indoors during the holidays in a Portland home with clean, healthy indoor air.
By Rodger Brown December 31, 2025
Hosting more this season? Improve holiday indoor air quality in Portland with better filtration, duct cleaning, and HVAC support from Clean Air Act.
Outside view of snow covered Portland, OR to represent the need for furnace tune-up this winter.
By Rodger Brown November 26, 2025
Prevent breakdowns, reduce safety risks, and lower heating costs with a furnace tune-up in Portland, OR. The Clean Air Act keeps your home winter-ready.
An Alpine forest with mountains covered with snow.
By Rodger Brown October 27, 2025
Sealed homes trap pollutants in cold months. Change filters, book HVAC maintenance, upgrade to higher-MERV filters, and add a dehumidifier to manage moisture and prevent mold.
Clear Air technician performing a fall furnace tune-up and filter change in a Washington home.
By Rodger Brown September 30, 2025
Prep for cooler weather with a furnace tune-up, fresh filters, smart thermostat settings, and clean ducts/registers. Get practical energy-saving tips for Washington homes.
Wildfire smoke impacts indoor air too. Learn why changing your air filters during wildfire season.
By Rodger Brown August 26, 2025
Smoke and wildfire in Washington representing why checking HVAC air filter is important.
Show More