How to Tell if Your Furnace Is Oversized

Having a furnace that’s too big for your space is extremely inefficient. There are two simple signs that indicate that your furnace is most likely oversized:

  1. Your furnace runs for a short period of time before shutting off
  2. Your home has uncomfortable hot and cold rooms.

Let’s go into more detail about each of these, or you can simply give our Framingham, MA heating repair experts a call now!

Call (508) 881-1500

Furnace Turns Off and On

An oversized furnace has short run times (or “short cycles”) because it’s quickly heating your home to the thermostat’s temperature setting. By short, we’re talking 10-15 minutes. Now, that seems like a good thing (especially on frigid nights), but it’s not for a few reasons:

1) It’s not very energy efficient

The AFUE rating (the efficiency rating) you see on your furnace assumes your furnace is running at a “steady-state operation” (basically like a car’s mileage on the highway).

But an oversized furnace will come on and cycle off before it can reach that steady-state operation level of efficiency. So you’ve got several short, inefficient bursts wreaking havoc on your energy bill. Think of this as the furnace’s version of “city miles.”

If your furnace is properly sized, it will stay on longer, running almost constantly on the coldest days. Visit another one of our blog posts so you can understand your furnace’s AFUE rating to get big winter savings!

2) It dramatically reduces your furnace’s lifespan

Short cycling wears down the mechanical parts of your furnace. It’s like if you constantly turned your car off and on every time you came to a stop light.

Uncomfortable Hot and Cold Rooms

Do you feel a massive heat blast coming from vents in certain rooms?

Once again, the oversized furnace strikes! Its heat output is far more than your home actually needs, so you’re left with a heat hurricane in certain rooms. Ironically, an oversized furnace can cause rooms farther away from the thermostat to be too cool for comfort.


Because when the furnace cycles off your home cools down from the outside in. By the time your thermostat, which is located on an interior room wall, feels a temperature difference and turns the furnace back on, the rooms farther away have already cooled down a good 5-7 degrees.

If your furnace is properly sized, it should have longer run times, distributing heated air more evenly throughout your home. Learn more about why some rooms in your home are colder than others here!

What Can You Do If You Have an Oversized Furnace?

  • To even out the heated air in your home, you can run your fan setting to “ON.” But this wastes even more electricity.
  • If you’re thinking of getting a new furnace installed, ask several HVAC contractors how they plan to size your new furnace.
  • If they respond with, a rule of thumb (i.e., a certain number of BTUs per sq. ft.) or just say they’ll replace your furnace with one of the same size or larger, look elsewhere.
  • A good HVAC contractor should do a Manual J heat load calculation or use the manufacturer’s sizing software.

Framingham Furnace Experts

If you’re having issues with your furnace, reach out to Nicholson! We can help with furnace repairs, installs and more!

Book Online

Our level of commitment to our customer and superior service is the reason you can find comfort in choosing Nicholson Plumbing, Heating & Air Conditioning.

Book Online

We Take Pride in Our Work

Read about all the great things our customers have to say about us!
  • Francis from Nicholson Plumbing and Heating was excellent. He was here to evaluate HVAC in our home. He was very patient and answered all my questions. He is also polite and easy to communicate with him. He explained technical concepts to me in layperson terms!

    - Shelley S.

  • Nicholson offered what is possibly the best customer service I have dealt with in a home repair situation.  I called them because I was looking to replace my very old furnace.  They came out to do an initial estimate, and then came back when I had some further questions about my options.  After installing the furnace, they ran into some problems with my air ducts.  This happened on a Friday, and the problem was fixed by Monday afternoon.  In addition to their excellent service, they did quality work at a fair price.  I would recommend them to anyone looking for an HVAC company in the Framingham area!

    - Melissa T.

  • Recently used these guys because my HVAC unit AC wasn’t working (first hot day of summer).  Showed up on time, wore booties, fixed the unit.  During the visit we talked about how my unit was having problems in the winter – which was resulting in NSTAR service calls of maybe 3-4 times per season (I am on a service plan with them).   He was the first guy to tell me WHY the problem was happening, and HOW to fix it.  I find it strange that all of the NSTAR guys etc. no one took time to point out how to fix the source of the problem…Very professional, smart.  I would use them again, and plan to for the fix on my heating unit!

    - Ben J.

Read Our Reviews

We’re Ready to Help!

(508) 881-1500
Call Now

Our Brand Partnerships

Nicholson Plumbing, Heating and Air Conditioning is the best and most reliable source for electrical service. We are proud to be Mitsubishi Electric Diamond Elite Contractors, that have gone through extensive accreditation and training in order to provide proven high-quality service. Get in touch with us whenever you need to have electrical work done in Framingham!

Learn More