The first step in properly designing a heating and air conditioning system intended for a residential application is A Manual J load calculation, (using an Air Conditioning Contractors of America- ACCA approved software). This method of design is now required by Building Codes in most municipalities Nationwide. While some HVAC contractors view the Manual J calculation as an unnecessary burden, professional- HVAC contractors interested in providing their clients with the best product know that the only proper design process uses the Manual J calculation. Manual J will correctly determine the total amount of heat that is lost through the exterior of a home during the cooler months, and the total amount of heat that is gained through the exterior of a home during the warmer months. Using advanced calculations and inputs, Manual J analyzes all aspects of the thermal characteristics of every wall, floor, ceiling, door and window. Additionally the load calculation also takes into consideration other factors such as the home’s geographic location, orientation to the sun, envelope tightness, duct leakage, lights and appliances. ACCA’s Manual J even calculates the amount of heat and humidity that each occupant of the house adds to the interior of the home.
There are two types of load calculations. For new construction or existing homes with deficient duct design, the Room to Room method is required. For existing homes with sufficient duct systems, the Whole House or “Block Load” method may be used.
Room to Room
ACCA’s Manual J’s room to room calculation determines a heating/cooling load for each conditioned room in the home. It also provides the necessary airflow values to deliver the proper heating and cooling BTUs to each room. ACCA’s Manual S Equipment Selection Process uses the Manual J Calculations to properly size and select the best system. The room to room values are then used to design the ductwork distribution system with ACCA’s Manual D duct design method. Room to Room airflow values are also used to properly balance the airflow of the entire system during the (historically overlooked) commissioning phase of installation.
Whole House or Block Load
Whole House or Block HVAC Load Calculations provide the heating and cooling loads for the entire home. This type of load calculation is used when there is no need to design or modify an existing duct system. Whole house load calculations are commonly used to determine the correct HVAC equipment size and match-up that is required when replacing the HVAC system in an existing home.
HVAC contractors and builders don’t need the added stress of facilitating in house design. Our ACCA Certified Residential Design for Quality Installation professionals use the Wrightsoft Right-Suite® Universal , the number one ACCA approved software, to provide you with a detailed, accurate and timely Manual J Residential Load Calculation tailored to fit the needs of each individual project.
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