Are you thinking about buying a new air conditioner? If so, no doubt there are a variety of factors that you’re considering. One of the most important? Ensuring that you get a properly sized unit for your home or office.
If the unit that you select is too small, it may be cheaper upfront than a larger unit, but it will cost more to operate because it won’t properly cool your space and will run for longer periods than is necessary. It also will have a shorter operating life because it’s working harder than it needs to. Conversely, a unit that is too large will not dehumidify your indoor air properly, and create a damp chill rather than a comfortable, evenly humidified coolness. This can foster undesirable moisture, which can lead to mold and mildew in your indoor air.
Calculating just the right size with manual J
Manual J is a calculation that you can use to determine the ambient amount of warm and cool air that you need to create a comfortable indoor environment. Manual J also is known as a heat or cooling load calculation. This calculation considers the hottest or coldest days and times, along with the latent cooling load, which uses the wettest days, to determine the optimal amounts of heat and moisture to add or remove from the indoor area. The three loads are used to select the machinery required for optimal air operations and correct unit sizing.
Block loads versus room-by-room loads
Manual J protocol calculates the heat or cooling loads for a building, and you also can calculate loads room-by-room or in a block manner:
- The room-by-room load method: This is more detailed, and it more accurately determines how much air is needed in each room, which can help you determine proper air-duct sizing and the number of thermostats that you need. It’s used in new construction when designing HVAC (heating, ventilation and air conditioning) systems.
- The block load method uses the total heating and cooling loads for the whole building. You can use it when you are replacing a unit, but not adding ductwork, or when you’re making any design changes to your indoor air system.
For more expert advice about Manual J, proper HVAC loads, and other issues related to home comfort, contact the experts at Paschal Heat, Air, Geothermal and Generators. We proudly serve customers in the Northwest Arkansas area, and can help you with all of your heating and cooling needs.
Our goal is to help educate our customers about energy and home comfort issues (specific to HVAC systems). For more information about sizing your new air conditioner and other HVAC topics, download our free Home Comfort Resource guide.