Should You Install an Oversized HVAC System?

Bigger is not always better. Think back to what you learned in technical training for installing and maintaining HVAC systems. Sizing equipment for a particular home or commercial space should be your first consideration and calculation when creating a quote to replace an existing system.

Designing an HVAC system should be harmonious with the architecture of the building. Deciding on the HVAC design early in the planning process ensures that energy code requirements from the Department of Energy (DOE) are met. Bringing an entire building’s architectural and engineering requirements under scrutiny will result in planning an ideal HVAC system installation. Are there spaces for proper ductwork? Is the ventilation designed right?

As a comfort advisor, delivering the safest, healthiest, most comfortable, and energy-efficient system possible is your goal. Sizing matters. How much heating and cooling capacity is needed to keep people comfortable year-round?

Regardless of if your customer already has an existing system, the best practice is to perform a proper load calculation to assess the building and remeasure the space. Other factors, such as ductwork design and local climate factors should be taken into consideration. Often, homes and commercial spaces have been remodeled. Are the windows and doors leaky? Are the vents positioned well throughout the space? Does the home or space have hot or cold spots? Accurately assessing the space may improve customer satisfaction, reduce callbacks, and decrease your liability!

What Makes an HVAC System Oversized?

First, it is important to understand how heating and cooling systems are measured. Furnaces are typically measured in British Thermal Units, or BTUs, “which is the unit used to measure thermal (heat) energy. Specifically, it is the amount of energy needed to raise 1 pound of water 1°F at sea level.”

Meanwhile, air conditioners are usually rated in tons, with a single ton of nominal cooling equaling 12,000 BTUs. A 4-ton AC unit produces approximately 48,000 BTUs of cooling capacity.” For residential jobs, every home requires a particular amount of heating and cooling capacity for optimal comfort. An oversized HVAC system provides a higher capacity in relation to its size. For instance, a home that only needs 24,000 BTUs of cooling capacity won’t benefit from an HVAC system offering double or triple that capacity.

What Issues Does an Oversized System Have?

Installing an oversized HVAC system could create uncomfortable indoor air temperatures. An HVAC system with excess capacity can heat or cool your home faster, but that speed often results in other potential issues. Equally distributed heating and cooling will not be possible, resulting in hot or cold spots throughout your customer’s home or commercial space.

In cooling mode, properly sized HVAC systems dehumidify the air as it is cooled. Oversized HVAC systems don’t usually run long enough for dehumidification to occur – resulting in humid, clammy, and uncomfortable indoor air.

If that’s not enough, having too much capacity may also result in higher energy costs over time. A situation known as “short cycling” can wreak havoc on your HVAC system if left unchecked. The continuous starting and stopping may add additional wear and tear on the compressor, blower fan motor, and other HVAC parts. Oversized units tend to blast your interior space with cool air rather than cooling it down gradually. Temperature swings prompt the system to start up and shut down in rapid succession.

A residential heating and cooling system can last 10 to 20 years with proper maintenance. However, most oversized HVAC systems may not last that long due to short cycling issues. Additionally, if a system is not properly sized, you are at a higher risk for component failure sooner than those that are properly sized.


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