Signs You Have An Oversized Furnace And What To Do About ItBigger isn’t better when it comes to your heating system! An oversized furnace causes excess wear and tear, higher energy bills, and more problems (and expenses!) that make it tough to stay warm in the winter. 

This article goes over how to tell if the furnace installed in your home is too big. Then we’ll review why it’s a problem. Finally, we’ll walk you through some options for fixing the problem. 

And, if you have questions about the furnace installed in your home in York, PA, Manchester, or anywhere in South Central Pennsylvania, click below or call Air Comfort for a free consultation. 

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1. Oversized Furnace Signs 

1.1. Short-Cycling

1.2. Rooms Get Too Cold 

1.3. Cold Air Through The Vents

  1. Undersized Vs. Oversized Furnace 
  2. Why An Oversized Furnace Is Bad

3.1. More Expensive To Run

3.2. More Repairs, Shorter Lifespan

3.3. Cracked Heat Exchanger 

  1. What You Can Do About An Oversized Furnace

4.1. Extend Ductwork

4.2. Replace Furnace

  1. Heater Replacement In York, PA

Oversized Furnace Signs 

Three signs your furnace may be oversized are: 

  • Short-Cycling

  • Rooms Get Too Cold 

  • Cold Air Through The Vents

If you’ve only noticed these recently, it’s probably due to a different and new issue with your system. But, if these problems have occurred year after year, a heater that’s too powerful is likely the root cause. 


Short-cycling is when the system only runs for a minute or so, turns off, and then turns back on again. Conventional forced-air systems usually run for 10 to 15 minutes at a time. Once the temperature reaches your thermostat setting, it turns off until it gets too cold again. 

There’s a problem when that happens too quickly. An oversized furnace pushes way too much hot air into your home at once. It jolts the temperature up, so the system turns off. 

But, it doesn’t provide enough heat for long-lasting comfort. Instead, the temperature quickly drops again. 

Read More: Why Does My Air Conditioner Keep Turning On And Off

Rooms Get Too Cold 

When the heater doesn’t stay on as long as it should, it doesn’t warm the entire house. And, the upstairs rooms usually get the worst treatment. The second floor is often colder in the first place. Then, add that the furnace doesn’t stay on long enough to circulate enough air all the way up through the ductwork. 

Cold Air Through The Vents

If you have the heat on and notice cold air coming through the vents instead of heat, there’s a big problem. Your furnace does this when the inner components run the risk of overheating. 

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When your system produces too much heat for the space it’s treating, that warmth backs up into the system. Your furnace isn’t made to store heat. As a failsafe, the system starts blowing cold air to cool down the components. 

Read More: Why Does My AC Blow Warm Air? 

Undersized Vs. Oversized Furnace 

Ideally, your HVAC contractor does the proper load calculations to ensure you have the right-sized system for your home. That takes into account square footage, room layout, windows, insulation, and more. 

Still, we see homes with furnaces that are just too powerful. But the truth is, you’re better off erring in the other direction. 

An undersized furnace will also leave you with high energy bills and a home that’s too chilly. The system isn’t powerful enough to keep up. And, it will use a lot of gas, oil, or electricity trying to do so. You’ll wear out that system, but an oversized furnace is more likely to break down or cause a health hazard. 

Why An Oversized Furnace Is Bad

My Heater Is Blowing Cold Air | Heater Repair Hanover, PAWe’ve briefly mentioned some of the reasons an oversized system is no good. But, the problem goes much further than just a chilly room or two. The potential pitfalls include: 

  • Less Comfort Overall

  • More Expensive To Run

  • More Repairs, Shorter Lifespan

  • Cracked Heat Exchanger 

Less Comfort Overall

The system will turn off before it does the job. And, it may even start blowing cold air into the home. 

More Expensive To Run

Your furnace uses the most energy when it’s starting up, not when it’s running. With a short run time, it uses more energy than usual to start up over and over again. That means higher bills.

More Repairs, Shorter Lifespan

There’s a lot more wear and tear with all that stopping and starting. Belts, blower motors, and other parts break down faster than they should. Even if you keep paying all that money in repairs, you’ll still end up with a larger bill before you expect it: All that damage takes its toll. 

Read More: Are Furnace Inspections Important?

Cracked Heat Exchanger 

The all-too-common worst-case scenario here is the cracked heat exchanger. That’s a ceramic housing inside the system where combustion takes place. That process produces carbon monoxide, which is deadly but escapes safely outside through exhaust.

When the heat exchanger cracks, that CO leaks out of the system and into your home. And, the number-one cause for a cracked heat exchanger is excess stress from sudden, drastic shifts in temperature. And, there’s no practical way to replace that part. In most cases, you need a new system altogether. 

What You Can Do About An Oversized Furnace

Unfortunately, you don’t have many options if your furnace is oversized. We’ll walk you through your two choices. But, be warned: The second one is often the most practical. 

Extend Ductwork

Sometimes, we can add more ductwork so that extra heat and pressure have somewhere to go. But, it’s expensive and may require a lot of work on the house. The job can run thousands of dollars. 

Replace Furnace

The bad news is that the best way to “fix” an oversized heater is to get a new one that’s appropriately sized. It’s expensive upfront, but the best way to be sure you’ve solved the problem. The good news is that today’s heaters are much more effective and efficient. So, you’ll get a comfort upgrade with lower monthly bills. 

Heater Replacement In York, PA

Click below or call to reach us at Air Comfort for information on a heater replacement in York, PA, Manchester, or anywhere in South Central Pennsylvania. We have an excellent reputation and will make sure to take all the necessary steps, so your new system is the perfect fit for you and your home.

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