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Why Home Heating and Cooling Systems Must be Properly Sized

By Angell Aire /

A central heating and cooling system, the HVAC (Heating, Ventilation, and Cooling) system, is one of the hardest working systems in the home. It is tasked to keep the occupants cool in the summer and warm in the winter, but there is a hidden summer task as well.

The system in the summer must also remove humidity from the air, as the higher the humidity, the lower the thermostat must be set for comfort. The humidity is removed by condensation on the indoor coil. It is very cold and condenses the moisture out of the air, which goes down the pan drainpipe. This is important to the sizing discussion next.


Cooling System Sizing Importance

It would seem to some, especially in the value-add mindset, to assume that upsizing the cooling system would do a better job. They may perceive that if it doesn’t run as much on a hot day that they’re also saving money on electricity. There are both efficiency and comfort problems with oversizing the cooling side of the system.

A unit that’s too large and cycling on and off a lot is using as much or maybe more electricity than a smaller one running longer. The larger compressor uses more electricity, but there’s another reason for proper sizing. The compressor pulls its highest current load when it starts. The high current also creates more heat in the motor windings. Over time, many more startups than necessary can and often do decrease the life of the compressor.

The comfort problem with oversizing the unit is that the humidity removal task is hampered. If the unit is shutting down a lot, it isn’t removing humidity, and the occupants must turn down the thermostat to feel more comfortable. This is both a comfort and an energy consumption issue. The properly sized unit runs longer, removing more humidity, and keeps the home comfortable at higher temperatures.


Heating System Sizing Importance

An oversized furnace, particularly gas fueled, will also cycle off more often. Each time it comes back on, the heat exchanger must be heated to a specific temperature to kick in the blower, and the ductwork must be warmed up as well. So, a smaller unit running longer will keep that heat exchanger and ductwork warm longer and operate more efficiently.

An oversized furnace results in frequent cycles and wider temperature swings in the home. At times the occupants feel comfortable, while between cycles they can begin to feel a bit colder than they like. Sizing the furnace properly solves the comfort and efficiency issues.


Keeping these equipment sizing tips in mind, the homeowner will understand when the HVAC specialist does a heating and cooling load calculation for the home and recommends a properly sized unit. Contact us today if you have any further questions about new HVAC equipment or to schedule an appointment.


"Jason was very professional and knowledgeable. He gave a summary of everything he did and how our furnace and AC are performing based on their age. Fortunately, we had a good check up and he didn't try to sell us any replacement parts that we didn't need. Highly recommend!"

S. Swanson -
ac company

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