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Performing a Load Calculation When Installing New HVAC Equipment is Imperative

  • Air Conditioning

When facing an expense of several thousand dollars for a new furnace, central air conditioner or heat pump, you should take all steps necessary to select an HVAC system that will work effectively, efficiently and will be reliable for many years. Your new equipment must be correctly sized to properly heat or cool your home. To determine what size HVAC equipment you need, you must know your home's heating and cooling loads. To find those loads, an HVAC professional must perform a load calculation.

What is a load calculation?

A load calculation is a detailed and precise method used to find out exactly how much heating and cooling is needed to keep your home at the temperature you prefer. After doing an on-site inspection, taking numerous measurements and evaluating the comfort requirements of you and your family, your HVAC expert will be able to produce an accurate quantitative measure of heating and cooling needs. Performing a load calculation takes into account the unique thermal and structural characteristics of your home and your geographical area, such as:

  • Local weather, temperatures and climate
  • Size, shape and directional orientation of your home
  • Airtightness of your home
  • Air leaks in your home's seal and ductwork that could lead to conditioned air loss
  • Amount, type and location of insulation
  • Number, location, directional orientation and types of windows
  • Number of lights and appliances that produce heat
  • Type of construction materials used to build the home
  • Landscaping, including trees, shrubs and earthen barriers that could affect how much wind, sunlight and other natural elements reach the home
  • Number of occupants in the home and occupant lifestyles
  • Energy efficiency of the home and steps taken to increase efficiency, such as sealing ducts and air leaks, adding insulation and weatherstripping or putting in new windows
  • Homeowner and occupant temperature preferences

The need for proper equipment sizing

Proper sizing of HVAC equipment means selecting and installing systems that are big and powerful enough to provide all the heating and cooling you need without being so big that they waste energy, overheat or overcool. When you know your home's heating and cooling loads, you'll be able to choose HVAC equipment that's properly sized to meet those loads.

Manual J load calculation

The industry-standard procedures for performing a load calculation are contained in Manual J, "Residential Load Calculation," a guidebook published by the Air Conditioning Contractors of America (ACCA). The manual contains all the instructions and technical steps required for an accurate load calculation of your home. It gives your HVAC professional tested and proven guidance on how to account for the details and variables in your home's structure.

After performing a load calculation, your HVAC source should have numerical results showing the following:

For heating systems

  • Sensible heating load: Sensible heat is how much heat can be felt, or sensed, and measured with a thermometer. This heating load is the amount of heat that your HVAC equipment should be able to generate during the night (when there is no additional heating available from the sun) on days that are nearly the coldest of the year.

For cooling systems

  • Sensible cooling load: The sensible cooling load is the amount of sensible heat that your cooling system should be able to get rid of during daylight hours on very warm days.
  • Latent cooling load: The amount of moisture the cooling system should be able to remove during hot, humid summer days. It determines how much energy is needed to dehumidify your indoor air during these types of days.

When your HVAC specialist is performing a load calculation, keep the following factors in mind:

  • The most recent version of Manual J should be used.
  • Heating and cooling equipment recommendations should be based on expert interpretation of the heating and cooling load data.
  • Heating and cooling systems should be no more than 15 percent oversized.
  • Use the ACCA guidebook, Manual S, "Residential Heating and Cooling Equipment Selection," for industry-standard assistance with choosing the right HVAC equipment to meet your home's heating and cooling loads.

Customers can turn to the experts at for professional ductless air conditioning and heating sales, installation, maintenance and repair. Contact us today for more information on the importance of performing a load calculation and installing properly sized heating and cooling equipment in your home.

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