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Your Air Conditioner Installation: Where Manual J and Manual D Come In

The hot, humid summers in the Houston and Galveston areas mean air conditioner installation is something you’ll need to take seriously if you expect to stay comfortable and avoid sky-high energy bills.

While some less-than-diligent contractors use imprecise rules of thumb during the installation process, reliable contractors follow proven guidelines for accurate A/C and duct sizing. These guidelines are laid out in the ACCA’s (Air Conditioning Contractors of America) Manual J and Manual D.

How Manual J helps

Manual J sets forth a process for calculating your home’s cooling load, or how much power it will take to keep your home cool. Your cooling load, in turn, determines the size of air conditioner you’ll need. The old rule of thumb considers only your home’s square footage, which almost always results in an oversized, inefficient, poorly performing system. To determine the right system size for optimal energy efficiency and performance, Manual J accounts for many factors related to your home, including:

  • Size and floor plan
  • Sun orientation
  • Air-leakage rate
  • Amount and type of insulation
  • Number, location, and type of windows
  • Heat-producing appliances and lighting
  • Number of occupants

Your contractor collects data on all the factors listed in Manual J and enters these data into a software program to work out the best A/C system size for your needs.

How Manual D helps

Manual D is used to design new duct systems or review existing systems for any improvements they may need. The guidelines it presents help your contractor ensure your ducts will distribute cool air evenly and efficiently. Duct system improvements may involve anything from simple additions such as jumper ducts and transfer grilles to more complex projects such as installing larger ducts. Manual D accounts for factors such as:

  • Required airflow to each room
  • Air handler location
  • Blower power
  • Length of the ducts
  • Type of duct material

If you want your new air conditioner to perform as effectively and efficiently as possible, contact us at Davis Air Conditioning & Heating, Inc. We can help you with your air conditioner installation and other home comfort needs wherever you are in the Houston, Angleton, Ft. Bend, Galveston, Sugar Lane or Brazoria areas.


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