Proper Sizing Is Extremely Important When It Comes To Your HVAC System – Bigger Is Not Better

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Proper Sizing Is Extremely Important When It Comes To Your HVAC System – Bigger Is Not Better

Bigger Is Not Always Better

  • Over sized systems also use more fan power for the blower and often exhibit more duct leakage due to high operating duct pressure.  Finally, over sized air conditioners and heat pumps greatly aggravate the summer utility peak demand on hot days.

Use the right contractor

  • Beware of casual sizing estimates based solely on an old school formula of “dividing the square footage of your home by a number to obtain tonnage”.  The residential equipment sizing procedures recommended for use in the United States are found in Manual J, which is produced by the Air Conditioning Contractors Association of America (ACCA). Computer programs are available to simplify the load calculations specified by Manual J.  Once the heating and cooling loads are known, Pleasant Air will then select compatible equipment for you.
  • Unfortunately, ACCA approved sizing methods are often not used and over sizing is very common. In one large-scale survey, nearly 40 percent of contractors indicated that they purposefully over-sized equipment, citing reason such as “to reduce call backs”, “to allow future expansion”, or “customers demanded it”.

Sizing and Efficiency Go Hand In Hand

  • Manual J procedures determine the design and heating and cooling loads based on the amount of wall, ceiling, window and floor area, their insulation value, and the building envelope and duct leakage.  Building orientation, roof surface color and occupancy can also make a difference.  The sizing calculations for new construction should take into account the various efficiency measures incorporated in the home.  As a home’s efficiency is improved, the recommended size of the HVAC system should be reduced.
  • Pleasant Air Inc. has a team of individuals who are certified in all Manual J procedures and have years of experience in properly sizing the Heating and Cooling needs of your home.

How To Determine the right size for your home

  • Insist that documented sizing calculations be performed on your home using the ACCA Manual J procedure. ACCA methods have sufficient built-in safety factors to accommodate most air conditioning needs.  Therefore, it is important to follow all instructions in Manual J using precise area measurements and other specific data.
  • Be aware that exaggerating temperatures for indoor heating and cooling set points can have large impacts on required equipment sizing. Generally, Manual J recommends 75 degrees for cooling and 70 degrees for heating.
  • Select a programmable thermostat so that your home can be conditioned before you arrive, thus avoiding the temptation to over-size equipment for rapid cool-downs or warm-ups. This will improve sizing-related performance and potentially save energy associated with more reliable thermostats.
  • Select variable speed air handlers to gain important advantages for both humid and dry climates. In humid climates, many variable speed systems “ramp up” blowers slowly, providing energy savings and improved dehumidification.

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