Why Does Air Conditioner Sizing Matter?

image of tape measure depicting air conditioner sizeThe summer season puts a high demand on the capacity of cooling systems, so much so that it tests the limits of old air conditioners. Unfortunately, even well-maintained AC units fail to handle the high heat and start to break down more often. When and if this happens, the air conditioner will have to be replaced. Getting an AC replacement should be easy and straightforward. However, there are so many options that choosing the best brand, size, and model can get confusing.

Most homeowners prefer to stick to the same brand or similar model but this does not always guarantee the best results. There is also that very common mistake of buying the biggest air conditioner unit available. Many believe that it will be more effective in cooling the home more quickly. Have you made these mistakes or are you about to? Find out why where cooling comfort is a priority and air conditioner sizing matters.

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Understanding The Importance Of Manual J Load Calculation

The Manual J load calculation is a necessary process needed to determine the correct capacity of the air conditioning system that will be installed in a given space, such as a home or building. The process is rather complex and requires the consideration of different factors. This includes the intricacies of the design and existing ventilation systems of a given space.

HVAC contractors often utilize advanced software for a quicker and more precise calculation of the Manual J load. There are house characteristics that have to be quantified, including

  • the floor area
  • house orientation
  • ceiling height
  • air leakage
  • window sizes
  • building materials
  • number of occupants
  • insulation

Even the heat generation level of appliances must be included in the calculation to determine the required cooling load of a building. The Manual J load calculation takes away all the guesswork regarding the ideal air conditioner size. This way, you know exactly what you need to buy.

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Achieving Home Comfort

image of a happy family with new air conditioning unit

Air conditioners are designed to deliver and maintain indoor comfort. However, its cooling capacity is just one aspect of its design. Air conditioners are also meant to reduce indoor humidity. The evaporator coils inside the AC system turn vapor into beads of water that flow through the channels.

If the unit is oversized, the air conditioner will cool down the air so quickly that the cooling cycle ends even before condensation can occur. With high humidity, the indoor environment will feel sticky and uncomfortable. To compensate, people often crank up the AC in an attempt to reach the ideal temperature, thereby increasing its energy demand. Oversized air conditioning units also tend to perform shorter cycles which contribute to poor indoor air quality. This happens because the air conditioner system has to force a reduced amount of air through the filters, affecting the cleaning process as a result.

Conversely, an undersized air conditioner also makes the problem of comfort worse. First, it cannot perform well enough to cool down the home. To reach the desired temperature, the unit will have to work for a longer period than is necessary. A small unit, for example, will not cool down your room on an especially hot day when the sun is beating mercilessly on your roof. Even if the air conditioner works harder, it will still fail at getting to the target temperature. Because it has to run on a high level constantly, the AC unit will eventually succumb to premature wear-and-tear and eventually require frequent replacements and repairs.

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Air Conditioner Efficiency

image of energy efficiency

The best air conditioner that will run efficiently is one that has an excellent SEER rating. This rating indicates how well the unit converts electrical energy to cooling capacity. When considering the SEER rating of the AC unit, it is also important to look at its size – not the physical measurement but its cooling power when other factors are taken into consideration.

If the unit is mismatched with the space it is meant to cool, it will still fail to fulfill its optimum SEER rating. When this happens, expect prolonged or shortened cycles. The AC unit will also consume more energy and become more susceptible to increased wear and tear. Installing a brand new air conditioner that comes with a good SEER rating will not be a solution to your cooling problem if it is the wrong size.


Cost Of Air Conditioner Operation

As long as the air conditioner is mismatched, it will require a higher cost of operation. You will have to spend more on the unit itself and on its energy consumption. Keep in mind that air conditioners with a higher horsepower (and increased cooling capacity) cost more. Because it is mismatched, it will cycle frequently, wasting more energy and exposing its parts to premature wear and tear. The stress on the parts and components of the AC system will soon lead to increased repairs and replacements. With proper sizing, unnecessary air conditioner expenses such as these can be avoided. Although the Manual J load calculation is a paid service, it is worth the small expense.

What’s Wrong With Oversized Air Conditioners?

feeling hot and sticky due to high humidity levels

As mentioned above, the problem with oversized air conditioners is that they decrease temperatures too quickly, which causes the systems to short-cycle. This, in turn, makes the units inefficient in controlling humidity and maintaining the ideal indoor air quality. Because the unit is at its sub-optimal performance level, it consumes more energy than it needs. Essentially, it keeps the home cool but rather humid. It also forces you to pay more in terms of acquisition and operating costs.

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What’s Wrong With Undersized Air Conditioners?

Undersized ACs are, quite simply, incapable of cooling their assigned space. In the summer when you need an effective cooling appliance the most, it will fail to deliver. An undersized AC will have to work twice as hard (or even more so) as a regular-sized unit to cool a room but it will still fail. Parts and components will also be exposed to too much stress, which will later lead to early equipment failure and higher air conditioner repair costs.



Choosing an air conditioner is not about choosing the biggest and most impressive or the smallest and most affordable. Either choice will not guarantee optimal performance. Every home is different and homeowners have different needs. The best air conditioner is one that matches the unique need of the home it is meant to serve. AC size is a critical factor that should be considered carefully before having an air conditioner installed. It affects comfort, determines efficiency, and ultimately, influences cost. Avoid the rules of thumb you have gotten used to relying on. Talk to a trained and licensed HVAC contractor who can actually calculate the best air conditioner size for your needs using proven scientific tools.

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Call Townsend Energy For Your Air Conditioning Requirements

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Air conditioner size should matter to you. At Townsend Energy, we make sure that our clients in Northeastern Massachusetts, Southern New Hampshire, and Maine enjoy the best in terms of comfort and energy efficiency while keeping their cooling costs down. Our technicians are certified and highly capable of performing top-quality HVAC services such as tune-ups, installations, repairs, and replacements.

You are assured that every job we do is guaranteed to be the best in the area. Why settle for less when you can enjoy better comfort within your budget? To schedule your free, in-home estimate, call Townsend Energy for an appointment today.

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