How to Calculate Static Pressure in Ductwork: Design TESP and Field Reconciliation
How to calculate static pressure in ductwork: TESP formula, friction rate method, manometer measurement, and reconciling design vs field.
Guides & Resources
Practical guides for hvac design & load calculation professionals.
Whole-House Ventilation ERV/HRV Sizing: ASHRAE 62.2 Beyond the Formula
Whole house ventilation ERV/HRV sizing: ASHRAE 62.2 formula, climate-driven ERV vs HRV selection, and effective vs nominal CFM at the unit.
Free HVAC Load Calculation Software: What Contractors Are Using Beyond Wrightsoft
Free HVAC load calculation software for contractors compared: ACCA-approved options, the free-tier traps, and the gap from free to Wrightsoft.
Manual J vs Rule of Thumb: Why Oversized HVAC Systems Fail and How to Justify Proper Sizing
Manual J vs rule of thumb HVAC sizing: accuracy, time cost, permit acceptance, and the quantifiable costs of oversized systems. Comparison with worked numbers.
Manual D Duct Sizing: Total Effective Length, Friction Rate, and Common Errors
Step-by-step Manual D duct sizing: CFM per room, available static pressure, total effective length, friction rate, and five common errors that break duct performance.
Heat Pump Sizing for Cold Climates: Balance Point and Backup Heat Calculation
Cold-climate heat pump sizing with the three-number method: ASHRAE 99% design temp, Manual J load, and 47/17F capacity. Worked balance-point example.
Refrigerant Charge Verification: Superheat, Subcooling, and Field Diagnostics for Residential AC
How to verify refrigerant charge in residential AC systems using superheat and subcooling methods. Complete field procedure with R-410A worked examples, diagnostic matrix, and R-454B transition guidance for technicians.
Reading a Psychrometric Chart for HVAC Design: Properties, Processes, and Coil Selection
How to read a psychrometric chart for HVAC design. Step-by-step guide to the seven air properties, three real conditioning processes with worked numbers, and practical coil selection using SHR and apparatus dew point.
Air Changes Per Hour: How to Calculate Ventilation Requirements by Occupancy and Code
How to calculate air changes per hour for HVAC ventilation design. Covers the ACH formula, ASHRAE 62.1 and 62.2 requirements, occupancy-based vs. volume-based methods, and a worked office ventilation example.
BTU Requirements by Room Size: HVAC Sizing Rules Beyond the Square Footage Shortcut
How many BTU do you need to heat a room? The answer depends on six factors the square footage shortcut ignores. Decision guide for HVAC contractors with real numbers and sizing tables.
Room-by-Room Heat Loss Calculations: Manual Method for HVAC Sizing
Complete worked example of a room-by-room heat loss calculation for residential HVAC sizing. Real numbers, every formula step, and common errors that inflate your load.
Manual J Load Calculations: What Contractors Get Wrong and How to Do It Right
Learn how to perform a Manual J load calculation for residential HVAC projects. Step-by-step process with common mistakes, ACCA sizing limits, and real-world input tips for contractors.