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  • HVAC Sizing Requirements

    Right-Sizing Benefits

    • Residential Air Conditioning Systems have in the past been oversized costing home owners and providing less comfort.  Right-sizing the AC will reduce initial cost and improve comfort, and home owners will stop losing money.  Further information is at DOE Building America and the Pima County Green Building page.

    General Requirements

    • IRC M1401.3 requires heating and cooling equipment sizing per ACCA Manual S based on ACCA Manual J 8th edition.  IRC M1601.1 requires duct design by ACCA Manual D.
    • Submit: Manual J/S/D calculations at the time of initial plan review submittal. Plans without these calculations will not be accepted for review.  Exceptions:
        • New construction:
            • The home is participating in a utility sponsored energy efficiency program or the Energy Star for Homes program and provides proof of enrollment, or
            • A mechanical engineer provides sealed heating and cooling calculations and duct design or a registrant uses energy modeling.  For this exception, Manual S can be a deferred submittal due prior to calling for intermediate inspections.
        • Equipment replacement:  The replacement is part of a utility company program and a utility program application is provided.
    • Submit: the extended rating for the selected equipment indicating the sensible cooling capacity at the design temperature.  Calculate 1/2 the excess latent capacity per Manual S and add to sensible capacity. 


    • Check the ACCA webpage for ACCA approved software.  As of 12/9/16 the following software is approved by ACCA:
      • Wrightsoft Right-J8
      • Elite RHVAC
      • Adtek AccuLoads
      • EnergyGauge
      • CarmelSoft HVAC
      • Avenir Heat CAD
      • Cool Calc 
    • ACCA Manual J8 AE Speedsheet is a free excel down load for use with projects that meet the abridged version criteria as stated on the “Read Me” tab, including:
      • Single zone
      • Glass area <15% of Floor area
      • Dark Shingle Roof
      • Ducts in conditioned space
      • Few homes in Pima County meet these criteria.

    Design Parameters

    • Outdoor design temperatures:  See the amendments to the IECC
    • Indicate the infiltration factor used in the calculations:
      • New construction should be: Semi-tight or Tight
      • Equipment Replacement should be: Average, Semi-loose or Loose; or based on blower door test
    • Conditioned floor area:
      • New construction: per plans
      • Equipment Replacement: per Assessors record +/- 10%

    Equipment Sizing

    • Selected HVAC equipment sensible + 1/2 the excess latent cooling capacity shall be within +/- 6,000 Btuh of the design sensible cooling load.

    Report Submittals

    • Each software package prints different reports, provide only the reports noted
    • The following pages show the print screen for each of the software programs and note the required reports.
    • Sample reports are provided indicating the elements that will be reviewed.
    • Sample equipment extended ratings are provided at the end of the sample reports.
    • Energy software examples


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