Manual J 8th Edition is the national ANSI-recognized standard for producing HVAC equipment sizing loads for single-family detached homes, small multi-unit structures, condominiums, town houses, and manufactured homes. A proper load calculation, performed in accordance with the Manual J 8th Edition procedure, is required by national building codes and most state and local jurisdictions.
MJ8 produces equipment sizing loads for single-family-detached homes, small multi-unit structures, condominiums, town houses and manufactured homes.
Manual J8 provides detailed requirements for producing a residential load calculation per the CLF / CLTD method. The provision of the standard apply to any dwelling unit that has its own heating-cooling-ventilating system and equipment, and its own exhaust air system(s). This includes:
Manual J8 divided into two portions: normative and informative. Parts N (Normative Requirements) and 4 (Normative Tables) contain the minimum requirements for conducting a residential load calculations. Informative Parts 1, 2, 3, and 5 contain additional explanation, details, and examples that clarify the normative requirements.
Below is a detailed overview of changes in the updated 2016 version vs. the 2011 release of Manual J (version 2.11) is as follows:
3A-2 (Heat absorbing glass – windows)
3A-3 (Reflective glass – windows)
3C-2 (Flat heat absorbing glass – skylights)
3C-3 (Flat reflective glass – skylights)
3C-5 (Tinted plastic dome - skylights)
3C-6 (Milky plastic dome – skylights)
3E-2 (Latitude adjustment for generic fenestration)
3E-4 (SHGC values for light and dark shading devices used with generic fenestration)
8B (Moisture content of sea level air)
Single family detached structures, duplex structures, and triplex structures;
Single family attached structures (row house or town house);
Dwelling units in multi-family attached structures (condo and apartment units); and
Energy efficient homes.
New Section N: This nine page section provides the normative requirements for undertaking a load calculation per the CLF/CLTD method contained in Manual J, 8th Edition. It is intended to help with code enforcement. A new requirement in the documentation output is to indicate whether or not AED exists.
Design Conditions: Reference to the design conditions clarifies that the designer may use either the Manual J Table 1A/1B outdoor design conditions or weather data from ASHRAE, but that they cannot be mixed per Section 18-7. Guidance is also given for calculating the Grains Difference values from ASHRAE data.
Adjustable Defaults: Figure 3-1 (Adjustable Defaults for Local Conditions and Practices) has been expanded to include more information on rules for default use or default values. New topics addressed are: windows and skylight glazing assemblies; vertical glass – insect scree; vertical glass – sun screen; foreground reflectiveness; skylight tilt angle, exposure direction, and assembly U-value (Ueff); opaque panels; garage partition wall; encapsulated attics; infiltration; duct load factors and latent load factors; duct wall insulation R-value and duct leakage; duct wall surface area; AED excursion value; moisture migration.
Interpolation Rules for Software: Per Section 3, page 30: “Interpolation is required when rounding down, or up, from the actual variable value, or set of variable values, produces more than five percent (5.0%) difference between the rounded value and the fully interpolated value.”
Additional Section 3 Guidance: More detailed guidance has been added to Section 3 (Important Issues and Concepts) that covers: engineered ventilation as a system load; engineered ventilation as a space load; kitchen range hoods; fireplaces and space heating stoves.
Tables Deletions: The following tables from the 2011 Manual J have been deleted (See the Table Deletion Notice on page 256 for an explanation of why each table was deleted):
Revisions to varied Worksheets: Various revisions have been made to Worksheet E (Infiltration Loads), Worksheet GS (Duct Runs in Unconditioned Space), and Worksheet H (Ventilation Loads) in Appendix 10. These changes reflect the revised guidance on each subject, and have been incorporated into example problems throughout the informative portion of the Manual.
Informative Appendices: The following changes have been made:
Appendix 13 (ANSI ASHRAE Standard 62.2) in the 2011 Manual J has been deleted
New Appendix 13 (Load Calculations for Energy Efficient Homes)
New Appendix 14 (MJ8 Duct Loads for a Duct Leakage Test Specification)
New Appendix 15 (Load Calculations for Large Multifamily Dwellings)
In this issue, we present the Refrigeration Showcase, featuring new products from ice makers to reach-ins to display cases and more. We also look at heat pump technologies, how they benefit customers, and how you can service them.
Check back for additional content throughout the week.