Risks Associated with Oversizing HVAC Systems – Bigger isn’t Always Better

Oversizing any HVAC system will result in increased energy use, reduced comfort, indoor air quality, building, and HVAC equipment durability. The oversized comfort system will “short cycling” in both the heating and cooling modes. In order to reach peak operational efficiency and effectiveness, the HVAC system needs to run for as long as possible to meet the loads. Department of Energy uses the analogy of a car: “highway driving at a steady speed will get the best fuel economy, while speeding up and slowing down puts undue wear and tear on the engine and braking systems, and reduces fuel efficiency.”

Installation Cost, Energy Consumption Costs and Equipment Durability 

Installing an oversized HVAC system will have both a higher cost for installation and operation. Because the improperly sized equipment is frequently starting and stopping (short cycling), it is only a matter of time before the equipment experiences premature failure.

Personal Comfort Complaints – Space Temperature Issues

Rooms will not receive adequate duration of airflow because the short cycling limits the total amount of air circulating through each room. Because the spaces located further from the thermostat do not change temperature as quickly as spaces near the thermostat the short cycling oversized system


may lead to comfort complaints. Some rooms will be colder during the heating season and warmer in the cooling season even in an energy-efficient home. Because the occupants in the rooms further from the thermostat are uncomfortable, the occupant may set the thermostat set point higher, requiring additional energy.

Comfort – Humidity Control

Another risk with oversizing the cooling system, particularly in more humid climates, is cold clammy conditions can occur due to reduced dehumidification caused by short cycling. As air passes across the condensing coil the cooling system removes moisture from the air. A properly sized HVAC system will run long enough for the coil to reach a temperature where condensation will occur while an oversized system that short cycles may not run long enough to sufficiently condense moisture from the air viagra ligne fiable. Mold growth within the home is another negative result of excess humidity in the conditioned air.   

Right-sized HVAC system begins with an accurate understanding of the heating and cooling loads on a space. The values determined by the heating and cooling load calculation process dictate the equipment selection and the duct design needed to deliver conditioned air to the rooms of the house to meet the occupant’s comfort expectations. When inaccurate or inappropriate adjustments are applied during the heating and cooling load calculation process, seemingly small manipulations can result in exaggerated loads.