ACCA Certified Manual J Load Calculation Inputs For a Single-Family Home

It seems like every single day Savoy Engineering Group’s telephone rings with contractors who have just learned that their municipality now requires an ACCA Certified Manual J8 load calculation. These hard-working individuals| are intimidated by the new International Energy Conservation Code (IECC) requirements that are sweeping theUnited States.

After having completed thousands of HVAC Manual J Designs that have been submitted to LEED, Energy Star and numerous permit offices, Savoy Engineering Group wants to let you, HVAC contractor, know that the ACCA Certified Manual J process is involved, but should not scare you.

Let us look at what are the required inputs for a Single-Family Home when you see “HVAC equipment must be sized by an ACCA Compliant Manual J 8th Ed load analysis following ASHRAE Handbook of Fundamentals”.

Exact Building Orientation must be used instead of worse-case scenario.  Orientation of the Building can have a significant impact on room loads depending on the time of day and season.floorplans

Winter/Summer Indoor/Outdoor design temperatures.  International Energy Conservation Code recommends 70 F heating, 75 F cooling.  Outdoor design temperatures are based on ASHRAE weather tables and geographical location.

Sensible Heat Ratio (SHR) is the sensible/latent split for the total HVAC load.  Most municipalities use a 70/30 sensible/latent split or 0.70

How tight is your Residence? For new construction, average or semi-tight or average is the proper selection.  SIP and ICF construction is tight, while older buildings are semi-loose or loose.  Does your home have a fireplace?

How many people and appliances in your home?  ASHRAE recommends # of bedrooms + 1. Is your house mechanically vented?  ASHRAE recommends not exceeding 0.35 Air Changes per Hour (ACH).

Where is your Ductwork located?  Duct located outside the thermal envelope or conditioned space will have duct gains and losses. The amount depends on whether it’s a crawlspace, basement, garage or unconditioned attic.  Duct located inside conditioned space should not have duct gains and losses. Also duct length and insulation value is important.

Window losses and gains are critical.  Do you have single- or double-pane windows?  What about skylights?

Walls, ceiling and floors all have thermal losses and gains.  Is your wall masonry or frame? Is your roof flat or sloped? Light or dark roofing?  What about walls next to a garage? The roof floor above a garage or basement?  Use the exact, relevant materials in calculating the Manual J load calculation.

A good quality set of floorplans begins the ACCA Certified Manual J process.  The more accurate the data received by your design engineer, the more accurate your heating and cooling load calculation. Make sure your HVAC Manual J provider is qualified, is using ACCA certified software, isn’t over diluted and does ten other things besides Manual J load calculations, has easy to understand pricing and ACCURATE!