Make Heat Load Calculations Part of Your Pre-Construction Process

Designing a new home or business facility requires careful attention to the factors that will affect the ongoing costs associated with the new structure. From plumbing to indoor air quality to energy efficiency, the decisions made during the pre-construction process will have a significant effect on not only the comfort level, but also the monthly expenses of the building. One of the more important aspects of new construction is the proper heating of a new structure. Understanding how much heating is required for a new home, warehouse, office building or retail store requires that your construction or HVAC contractor perform a heat load calculation.

What is a heat load calculation?
A heat load calculation is a sophisticated mathematical method of determining exactly how much heating is needed to keep a home or other structure at the indoor temperature level its occupants prefer. All structures have a heat load (and a corresponding cooling load) that is based on structural characteristics of the building, steps that have been taken to increase the structure’s energy efficiency, and the comfort preferences of the people who will spend their time in the building.

What is involved in a heat load calculation?
When your HVAC expert conducts a heat load calculation, he will do an extensive on-site inspection of an existing building or evaluation of plans for proposed construction. With data from these processes, the technician will be able to produce an accurate quantitative measure of heating needs for the structure. A heat load calculation will take into account thermal features, structural characteristics, and local climate and geography, including:

• Area weather and temperature, including seasonal fluctuations and trends
• Shape, size and directional orientation of the structure
• Seal or airtightness of the structure
• Existing air leaks in the seal or ductwork, or ductwork design features that could cause energy loss
• Location and efficiency of vents, registers, and supply and return ductwork
• Amount, type and location of insulation
• Number, location and types of windows
• Number of appliances, lights and other devices that generate heat
• Type of construction materials used in the building
• Landscaping, including trees, shrubs, earthen barriers or other features that could increase or reduce the amount of sunlight, wind and other natural elements that can affect the structure
• Energy efficiency and steps taken to increase it, such as sealing air leaks, putting in energy-efficient windows and adding insulation
• Number of occupants and their temperature preferences

Why do a heat load calculation?
The information derived from a heat load calculation is vitally important to helping you and your HVAC contractor decide the correct size and capacity of heating equipment for the new structure. Proper sizing of HVAC equipment involves selecting and installing heating systems that are big and powerful enough to accommodate the structure’s heat load without being oversized or so big that they waste energy and heat inefficiently. When you know the building’s exact heating load, you and your HVAC contractor will be able to choose equipment that will provide the needed amount of heat.

What is the source of a heat load calculation?
Heat load calculations should be performed according to the procedures contained in Manual J, “Residential Load Calculation,” published by the Air Conditioning Contractors of America (ACCA). This manual sets out industry-accepted procedures, technical data and guidelines for conducting an accurate heat load calculation.

Additional factors to consider:

• Use the most recent version of Manual J.
• Accept and apply only expert interpretations of heating load data.
• Do not install heating systems that are more than 15 percent oversized.
• Use the ACCA guidebook, Manual S, “Residential Heating and Cooling Equipment Selection,” for authoritative information and guidance on choosing a heating system.

Our goal is to help educate our customers about Plumbing, HVACR, Fire Protection, and Alarm Systems in Mechanical, Commercial, and Residential settings. For more information about the importance of heat load calculations in the construction design process and to view projects we’ve worked on, visit our website!

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