Manual J and Manual D: Does Your HVAC Tech Know Them Chapter and Verse?

June 03, 2013

There are a number of factors that affect the size of air conditioner that your home requires. The best way for your air conditioning contractor to be sure that they’re all accounted for is to use Manual J and Manual D. Using the detailed calculation methods that these manuals provide will ensure that your cooling system is appropriately sized and designed.

The problem with oversizing

An oversized air conditioner will cost you throughout its life span. Larger air conditioners cost more to purchase and they’re less efficient when operating. They’re able to cool your home quickly so they turn on and off frequently. This is inefficient because they spend less time running at their ideal speed. This also makes them worse at dehumidifying the air since the evaporator coils don’t get as cold as needed and they therefore don’t remove as much moisture through condensation.

Manual J

Manual J enables the selection of an appropriately sized air conditioner by providing an accurate calculation of your home’s cooling load. It takes into account everything from your home’s location and insulation to the heat generated by the lighting, appliances and occupants in the home. It’s rather complicated, so most contractors use a computer program to help with the calculations. The results not only tell you how much heat that your air conditioner needs to remove, but they also tell how much moisture needs to be removed from the air. Your contractor should also use Manual S to determine which air conditioner will provide the correct performance levels for your South Alabama climate.

Manual D

Manual J also gives the cooling load of individual rooms. This is important when designing ductwork. The results should be used in conjunction with Manual D to ensure that the ductwork delivers the correct amount of cooling to each room.

If you want a contractor who will use Manual J and Manual D, contact the experts at Keith Air Conditioning, Inc. We’ve served Mobile and Baldwin county since 1964.