HVAC Math Handbook

Four hundred cubic feet per minute per ton. A constant of 1.08 on the air side and 500 on the water side. Every heating, cooling, and refrigeration technician runs on numbers like these - and almost nobody can say where they come from, or when they stop being true.

That is because the trade's arithmetic is scattered: a sizing table here, a manufacturer's bulletin there, a slide chart on the back of a pressure-temperature card, a rule of thumb passed down a shop until nobody remembers what it was derived from. It works until the job leaves standard conditions - a duct run at altitude, an air handler in a hundred-and-forty-degree attic, a nameplate that mixes two measurement systems. The technician who has only memorized the number is stuck the moment the table runs out. And a wrong number in this trade is never an abstraction: it is an oversized furnace, a starved coil, a callback, a compressor that dies young.

This handbook was built to close that gap. It gathers the calculations a technician actually performs - on a service call, at a start-up, during a replacement estimate - and works each one through from the physical relationship that produces it to the number written on the invoice. Where a shortcut exists, the derivation that justifies it comes first, along with the conditions under which it fails.

What you will take from it:

• One conversion method that handles any unit conversion, including ones you have never seen before
• The sensible, latent, and total heat equations - and how to correct their constants when conditions are not standard
• A complete heat loss and heat gain calculation, from design conditions to room-by-room equipment selection
• Airflow verified by duct traverse and by temperature rise, the fan laws, and duct sizing by friction loss against available static pressure
• The refrigeration cycle read from two gauges and two thermometers - superheat, subcooling, compression ratio, and charge limits for the newer mildly flammable refrigerants
• Combustion arithmetic: clocking a meter, input, output, efficiency, temperature rise, and gas pipe sizing
• Pump curves, glycol corrections, and expansion tanks on the water side; amperage, voltage drop, and power factor on the electrical side - through operating cost and simple payback.

The apparatus is built for learning and for the truck: 141 fully worked examples showing the equation, the substitution, and the units at every step; more than 400 end-of-chapter practice problems, each answered with a complete worked solution; a master conversion appendix with exact factors; every equation in the book collected in one place; reference data tables; a field quick reference; and a glossary of roughly 190 terms. Chapters are self-contained enough to open anywhere and cross-referenced enough to read straight through. Units follow United States practice, with an appendix for working any calculation in the units used across the English-speaking world.

It is written for the apprentice meeting this material for the first time, the trade-school or community-college student with an exam ahead, the working technician tired of trusting numbers he cannot check, and the estimator or service manager who checks them.

Stop working from numbers you cannot verify. Get your copy and start carrying the arithmetic that holds up when the table runs out.