Common Problems Caused By an Oversized furnace | Jerry Kelly (2024)

FAQs

What are the consequences of an oversized furnace? ›

It's important to make sure your furnace is the right size for your home. An oversized furnace can cause a number of problems, including increased energy costs, shortened furnace life, and uneven heating. If you're not sure what size furnace you need, talk to a heating and cooling professional.

Uncomfortable Hot and Cold Rooms

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.

If you live in a very hot or very cold region, you may want a system with a higher BTU rating to quickly respond to changes in the weather. In areas where the weather is more temperate, you can go with a smaller more energy-efficient unit.

An HVAC system with excess capacity can heat or cool your home faster, but that speed often results in a couple of other issues. First, your home won't benefit from gradual, even heating and cooling. As a result, you could end up with a number of hot or cold spots throughout your home.

The unit's lifespan gets shorter – If oversized units suffer wear and tear because of frequent short-cycling, undersized units suffer the same wear and tear, but for the opposite reason: failure to go through healthy on and off cycles.

A good rule of thumb for home heating is that you need 25 to 35 BTUs per square foot in the moderate climates that are typical throughout much of California, while you may need up to 45 BTUs per square foot in colder climates, such as those found north of Lake Tahoe.

A basic rule of thumb for furnace size calculation is that it takes 30 BTUs for every square foot of house. So, if you have a 1,000 square foot house, you need a furnace that has a 30,000 BTU output.

Thermostat Isn't Working

One of the most common furnace problems is a malfunctioning thermostat. A sure sign your thermostat isn't working properly is if your fan is constantly running. This will cause your thermostat battery to run, and cause your furnace to work inefficiently.

Average Life Expectancy of a Furnace

The average life expectancy of most furnaces and heating systems is about 15 to 20 years. However, boilers and electric furnaces tend to last 20 to30 years. Several factors can reduce or extend your furnace's lifespan.

Do high efficiency furnaces have more problems? ›

While high efficiency furnaces can be more costly to repair, they typically last longer, which can make them more cost-effective than traditional furnaces. High efficiency furnaces are ideal for homeowners who rely on their furnaces for at least a quarter of the year and are looking to reduce their energy bills.

An Oversized Furnace Causes Your System To Short Cycle

When you have a heating system that is too large, your thermostat will read a higher temperature. Consequently, your furnace will turn off too soon to heat the rest of your house. This dilemma is referred to as short cycling.

An oversized HVAC system cycles on and off more frequently than necessary. This short-cycling leads to increased wear and tear on components, reducing the overall lifespan of the system. It can also result in uneven heating or cooling, creating uncomfortable hot or cold spots in different areas of your home.

If you purchase an air conditioner with a higher BTU than needed, you will waste a lot of excess energy and the air conditioner will cycle off too quickly. Thus, an air conditioner with a higher BTU will not cool a room faster.

If your furnace is too big, it can cause parts of your home to be sweltering hot or unevenly heated and lead to a failing heat exchanger. The furnace will also cycle on and off too frequently, causing your furnace to wear out faster.

A furnace that is either too big or too small will lead to excessive fuel costs, potentially amounting to thousands of dollars annually. This extra expense does not equate to increased comfort; instead, it often results in uneven heating throughout your home.

Oversized Ducts

Larger than normal ducts are certainly capable of handling more airflow. But your HVAC system may not be equipped to pump that much air. In fact, your system needs a specific air pressure in the ductwork to properly distribute air.

Home Size Determines Furnace Size

It's recommended that a furnace has 30 to 60 BTUs per square foot. The actual number depends on the climate which we will get into in the next section. But, just for example, if you have a 1500-square-foot home and live in a warm climate, you will multiply 1500 by 30.