Acca Certified Manual J Load Calculation Inputs For A Single-family House

It seems like every single day Savoy Engineering Groups 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 intimitaded by the new IECC requirements that are sweeping the US.

After having completed over 3000 Manual J projects that have been submitted to LEED, EnergyStar and numerous permit offices, Savoy Engineering Groups wants to let you, the homeowner, 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 House when you see cooling equipment must be sized by an ACCA Certified Manual J8 load calculation following ASHRAE Handbook of Fundamentals.

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

Winter/Summer Indoor/Outdoor design temperatures. IECC recommends 72 F heating, 75 F cooling. Outdoor design temperatures are based on ASHRAE weather tables and geographical location.

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

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

How many people and appliances in your home? ASHRAE recommends # of bedrooms + 1. Is your home mechanically vented? ASHRAE recommends not to exceed 0.35 ACH.

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

Window losses and gains are critical. Do you have single- or double-pane glass? Do you have insect screens, interior shading, overhangs? What about skylights?

Walls, ceiling and floors all have thermal losses and gains. Is your wall masonary or frame? Is your roof flat or sloped? Light or dark shingles? 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 analysis.

A good quality set of houseplans begins the ACCA Certified {Manual J8 process. The more accurate the data received by your Manual J8 engineer, the more accurate your HVAC load calculation. Make sure your HVAC Manual J provider is qualified, is using ACCA certified software, isnt over diluted (does ten other things besides Manual J load calculations, has easy to understand pricing and ACCURATE!

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