6 Reasons You Should Not Install An Oversized Furnace

If you’ve found that your furnace has experienced a drop in efficiency or you’ve noticed an increase in utility costs, it may be a sign that your existing furnace is outdated and in need of replacement. But before you go out and purchase the latest and greatest model, it’s important to note that bigger is not always better. Finding the correctly-sized furnace for your home is, in fact, the first step in keeping costs low and ensuring optimal efficiency.

While, in theory, installing an oversized furnace may seem like a good idea, it can be excessive and actually make matters worse in a number of different ways.

Cost of Installation

If contractors are tasked with installing a large furnace, as a homeowner, you may be expected to pay extra. If the unit is too big for the allotted space, it’s entirely possible that fuel connections would have to be moved or adjusted to accommodate its size. Similarly, a large unit may not be compatible with your existing ductwork causing further complications that can only be solved with additional labor.

Short Cycling

With more power, a large furnace has the ability to heat a smaller home in less time than expected. This results in what is known as short cycling. The furnace will shut down after reaching the desired temperature, only to start up again shortly after and continue in this pattern. Not only does this cause an increase in noise with the constant start and stop, but it can do a number on components, increasing wear and tear and ultimately the likelihood of repairs and replacements.


Because of the constant short cycling caused by a unit too big for its home, your furnace will burn more fuel than should be necessary. A properly-sized unit should run for longer periods of time, free to heat your home accordingly. An oversized furnace, unfortunately, will never reach its true potential or run at the intended efficiency.

Higher Operating Costs

Unfortunately, once an oversized furnace is installed, the only way to fix the issues it causes is to replace the unit entirely. Instead, by keeping it, you’ll likely be burdened with high operating costs. Due to the constant starting and stopping, more fuel is burned and in turn, these costs rise.

Unrealistic Efficiency Ratings

Even if you purchase an efficient HVAC system, BTU capacity and AFUE ratings will not be accurate for an incorrectly sized unit. The system’s performance will never quite achieve its highest efficiency rating. In this case, paying more for an efficient yet oversized furnace will never actually pay off.

Uneven Heating

Short cycling causes more issues than just wear and tear on components and increased fuel consumption. It actually results in the poor balance of heating throughout your home. The starting and stopping of a system can leave certain parts of your living space too warm or even not warm enough. This is especially true for the area nearest to the thermostat.

The best way to combat these likely issues caused by an oversized furnace is to choose a unit that is proportionate to your home as it is. Though installing a large unit with the intention of adding an addition may seem like a good idea to heat a larger area in the future, it’s important to first calculate your present heating space. If you’re still unsure of what furnace size is right for your home, a licensed professional contractor can help you determine the best solution so you can keep costs low and efficiency high.

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