Sizing Ducts: The First Step Toward Installing Your New Air Conditioner

by Greg Leisgang on September 5, 2012

Posted in: Ductwork

sizing ducts, Cincinnati, OhioA central air conditioning system may be one of the most complex systems in your home, and sizing ducts in your home is critical to getting peak performance from it. HVAC professionals use several tools to determine the right size of equipment, including ducts, for your Cincinnati home. If the air conditioner itself is too large or the ducts are poorly designed, you'll lose efficiency. 

The process of sizing the system and the duct-delivery system involves using two industry tools. Manual J helps HVAC contractors find the right size for the air conditioner itself, and once they know that, they move to Manual D, which helps them calculate the best ductwork system size.

Energy-efficiency standards exist for air conditioners, but don't apply to the ductwork-distribution system since there are many variables that affect how the HVAC contractor needs to engineer the ductwork system itself. With good engineering, the ductwork will enhance the efficiency of the equipment.

The objectives that need to be met include:

  • Properly sizing the ducts to meet the manufacturer's specifications for airflow through them. Ducts that are too small make the air conditioner run longer, raising your electricity bills. Ducts that are too large create excessive noise, interfering with the enjoyment of your home.
  • Delivering enough air to each room, taking into account the cooling load in each. The second story and rooms with south- or west-facing exposure require more cooling because of solar heat gain.
  • Designing the supply and return system to balance the airflow to and from the blower 
  • Verifying that the ducts are well sealed to prevent air leaks. Leaky ducts contribute to higher cooling costs and can bring pollutants like dust and carbon monoxide into rooms, if your home uses any combustible fuels for heating. 
  • Locating the ducts -- and insulating them, if necessary -- so that the thermal losses are minimal 

If you're in the process of selecting a new air conditioning system and would like to learn more about sizing ducts, contact JonLe Heating & Cooling. We have provided HVAC services for the Greater Cincinnati area for more than 50 years and are a NATE-certified contractor. 

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