The Difference Between Manuals S, D and J

When you’re buying a new heating and air conditioning system, you have many choices to make. Sometimes it can seem overwhelming. What brand do you want? What size unit should you get? It’s a big investment, and one you want to get right the first time.

As you do your research, you may come across the terms Manual J, Manual S, and Manual D. You’ve probably figured out that they’re important, but you may not know what each term means. Here’s a quick rundown:

Manual J outlines the load calculations your HVAC professional performs when figuring out what size HVAC system you need. “Load” is the amount of cooling and/or heating your home needs. Load calculation involves figuring out the square footage and layout of your home. It takes into account factors that can affect the efficiency of your system such as the weather in your area, the types of windows you have, and the amount and placement of shade trees around your house. When done correctly, Manual J load calculations help ensure that your system efficiently heats and cools your entire house.

Manual S covers equipment selection. Not only do you have different types of heating and cooling equipment to choose from, but you also have different sizes of equipment. Choosing the wrong type or size for your home can result in higher energy bills — not to mention the unhappy family members who are always either too hot or too cold because the system isn’t functioning like it should. Manual S uses the load calculations outlined in Manual J to determine the best heating and cooling choices for your home.

Manual D outlines the calculations needed to choose and install ductwork. Improperly sized ducts can cause your system to lose efficiency and wear out more quickly. Using Manual D, your HVAC professional calculates the rate of airflow you will need as well as the the length and placement of new ducts.

For more information about how to choose the best heating and cooling systems for your home, contact Beyer Boys. We’ve proudly served the San Antonio area since 1990!

Our goal is to help educate our customers in the greater San Antonio, Texas area about energy and home comfort issues (specific to HVAC systems).

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