HVAC & Mechanical Reference Charts

ABOUT THESE CHARTS

These charts cover the look-ups sheet-metal and mechanical contractors make while sizing air systems: round duct CFM capacity at design friction rates, rectangular-to-round equivalents per the ASHRAE equal-friction method, friction loss per 100 feet, lab-measured flex duct capacity with the compression penalty, recommended air velocities, component static-pressure allowances, the CFM-per-ton and square-feet-per-ton rules, sheet metal gauge and weight, and the code minimums for duct wall thickness and hanger support.

On the refrigeration side, the charts give the pressure-temperature saturation data techs read off their gauges — R-410A, the new A2L replacements R-454B and R-32, and legacy R-22 — plus superheat and subcooling targets and methods, refrigerant line sizing by tonnage, a side-by-side refrigerant comparison (ASHRAE 34 class, GWP, glide), metering-device and TXV sizing, the run-versus-start capacitor reference, and the fan affinity laws.

For load and airflow design there are cooling and heating load rules of thumb, the BTU-ton-CFM conversions, the psychrometric properties and the sensible/latent/total heat formulas, ASHRAE 62.1 ventilation rates, air changes per hour by space type, diffuser and grille sizing, the ASHRAE 90.1 economizer rules, and combustion air sizing for fuel-fired appliances. Load rules of thumb are labeled estimate-only — a Manual J calculation is always authoritative.

HVAC authority is fragmented — ASHRAE, ACCA, SMACNA, the IMC/IRC, manufacturer data, and refrigerant property data each govern different tables — so every chart states its source and basis. Refrigerant P-T values are physical property data cross-checked against manufacturer charts; guidance, load, and equipment values are labeled typical or estimate-only and sent back to the data plate or the Manual J. When the answer needs computing instead of looking up, each chart links to the matching NORDIX calculator.