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Cooling/Heating Loads – Contractor

Ask yourself the following questions:

  • How much time do I spend designing when I could be selling and installing?
  • How much am I spending on staff to perform the HVAC design?
  • How much time, money and customer satisfaction am I losing due to incorrectly sized equipment or duct system design?

At Enerlogic, we provide accurate, independent, third-party HVAC design services that not only reduce your costs and warranty claim costs but also increase the quality of your work and clients’ satisfaction. You can take comfort knowing that your HVAC systems are properly sized, matched with the correct equipment and laid out accurately to provide optimal comfort and energy efficiency for your clients.

The Air Conditioning Contractors of America (ACCA) Manual J (8th Edition) – Residential Load Calculation for heating and cooling load calculations is the first of four steps in correctly designing an HVAC system. The HVAC design process should include the following steps:

  1. ACCA Manual J (Residential Load Calculation)
  2. ACCA Manual S (Residential Equipment Selection)
  3. ACCA Manual D (Residential Duct System Design)
  4. ACCA Manual T (Air Distribution)

With today’s high performance homes, using a “rule of thumb” approach just won’t cut it anymore. The ACCA developed these steps to ensure that you install correctly sized equipment and duct systems. Are you risking your business by not performing these steps?

The two methods for calculating a Manual J load are whole-house and room-by-room load.

Whole-House (Block) Load

The block load method provides the heating and cooling load for the home as a whole. It is typically used for a quick estimate of the building load or if there is no need to design or modify an existing duct system, which is not realistic in most cases. Whole-house load calculations are commonly used to determine the HVAC equipment size that is required when replacing an existing HVAC system. Unfortunately, this type of calculation inadequately determines new homes’ equipment selections, resulting in poor system performance.

Room-by-Room Load

The room-by-room method determines the heating/cooling load and airflow delivery necessary to properly heat and cool each room. To determine the proper individual duct sizes per room and the overall size and layout of the duct system, this information is absolutely critical. Otherwise, you will hear homeowner complaints regarding comfort in various rooms or zones of the home.

If a room-by-room load is incorrectly completed or not at all, rooms will have improperly sized ducting and balance (airflow) issues, leaving your client uncomfortable and unhappy. If the Manual J is completed correctly, but the Manual S used for matching the equipment and Manual D used to design the duct system are not completed correctly, the system will not perform.


Correct Manual J, S and D load calculations require a knowledgeable and experienced professional who can accurately determine and input the information into the approved software. Guessing or using assumptions is no longer an option for accurate load simulation.

If you would like to see an example of a Block or Room by Room load report, use the Contact Form to request a copy either of these.

Our staff at Enerlogic would be happy to answer all of your ACCA Manual J heating and cooling load calculation questions.

At Enerlogic we would be happy to answer all of your HVAC System design questions and provide you with design services in a timely manner.

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