MJ8 produces equipment sizing loads for single-family-detached homes, small multi-unit structures, condominiums, townhouses 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:
Single family detached structures, duplex structures, and triplex structures;
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:
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 screen; 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):
- 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)
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 14 (MJ8 Duct Loads for a Duct Leakage Test Specification)
New Appendix 15 (Load Calculations for Large Multifamily Dwellings)