• These data sets enable you to establish the specifications needed to collect “apples-to-apples” bids from HVAC contractors. The results let you identify which contractor is providing the quality installation you want versus a contractor who doesn't’t have the expertise you need.
• These performance specifications provide quality-control verification via duct-leakage, room-by-room flow rate testing, and so on, enabling you to see that the HVAC system matches (or does not match) what you paid for. Remember, “you get what you inspect, not what you expect.” The correct performance of the HVAC system is the key and to avoiding costly callbacks and even more expensive liability claims from your home buyers.

HOW TO DESIGN AN HVAC SYSTEM:

Loads and CFM Calculation

• ACCA Manual J Load Calculation or equivalent required;
• Calculate heat loss and heat gain for each room;
• Total room loads to determine system requirements.

Lay Out Air Distribution System

• Lay out duct system on floor plan and determine register positions and duct paths to optimize room air circulation and minimize duct length;
• Duct paths must account for locations and directions of joists, roof hips, fire walls, and other potential obstructions;
• Duct paths must be planned to avoid sharp turns of flex duct that will kink the duct.
  AJ Bair Mechanical LLC performs Manual J room-by-room loss-calculations to identify the “ideal” sizing of equipment and delivered flow rates for heating/cooling in every room for each plan/house. Although some HVAC contractors offer this type of calculation, here are a couple of good reasons for doing it yourself (using our services)

  Manual HVAC Sizing & System Performance Calculations

Size Air Distribution System

• ACCA Manual D Duct Design or equivalent required;
• Calculate correct cfm for each room and total for building for both supply and return;
• Size ducts according to Manual J loads, Manual D air flows, and final layout on plans;
• Choose registers to optimize air distribution and duct static pressure;
• Size and locate returns to optimize air flow per Manual D;
• For return-filter grills, calculate minimum return filter area per Manual D.

Select System

• ACCA Manual S Residential Equipment Selection or equivalent required. ACCA, 1515 16th St., NW, Washington, DC 20036, (202)483-9370;
• From Manual J loads and Manual D cfm, determine appropriate equipment
• Equipment should be sized to sensible loads;
• Equipment sensible capacity should not be more than 15% larger than the total sensible design load (as specified in Manual S).
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