HVAC Calculator: Load & Charge

HVAC Load & Refrigerant Calc is a professional engineering calculator suite built for HVAC technicians, refrigeration pros, residential heating contractors, and facility managers who need fast, accurate answers in the field. Fourteen purpose-built tools in one offline app — no subscription, no internet required. WHAT'S INCLUDED: Glycol Mix & Freeze — Calculate glycol concentration for any target freeze point. Duct Sizer Quick — Size round and rectangular ducts by airflow and target velocity. Chilled Water Flow — Compute GPM from tonnage and delta-T for chilled water loops. Superheat & Subcooling — Verify refrigerant charge on R-410A, R-22, R-32, R-134a and more. Refrigerant Charge — Diagnose over- or undercharge from subcooling and superheat, by refrigerant and metering device. Coolant Mix Ratio — Dial in propylene or ethylene glycol blends by volume, in US or metric units. Manual J Load Calc — Quick whole-house residential heating and cooling load estimates. Radiator BTU Sizer — Match radiator output to room heat loss in BTU/hr or watts. Boiler Efficiency — Fuel input, firing rate, stack loss, and annual fuel cost from boiler output and efficiency. Steam Trap Sizing — Size traps by condensate load, pressure, and safety factor. Tank Heat-Up Time — Calculate time and energy to bring a tank from start to target temperature. Heat Exchanger Duty — Solve Q = U A LMTD for counter-flow and parallel-flow exchangers. Insulation R-Value — Solve R-value from thickness, or thickness from a target R, across nine materials — with U-factor. Flue Gas Analysis — Combustion analysis from O2, CO, and stack temperature readings. WHO IS IT FOR: HVAC service techs diagnosing refrigerant charge and airflow on the job Refrigeration technicians working across R-410A, R-32, R-134a, and legacy systems Residential heating contractors sizing radiators and ductwork Commercial facility managers tracking chilled water and boiler performance Engineering students and apprentices learning load calcs and combustion analysis WHY HVAC PROS LOVE IT: Works 100% offline — reliable on rooftops, in basements, and deep inside mechanical rooms with zero signal. No tracking, no analytics, no account to create. No subscription — pay once, own it. Instant results — every calculator recomputes live as you type. Professional formulas based on standard engineering references, with inputs labeled clearly so you can trust every number. ONE-TIME UNLOCK: Three calculators are free forever. Unlock All Calculators is a single $12.99 one-time purchase (non-consumable, no subscription, no recurring charge) that opens every Pro tool — Superheat & Subcooling, Refrigerant Charge, Manual J Load Calc, Boiler Efficiency, Heat Exchanger Duty, Flue Gas Analysis, and the rest — plus reference tables for refrigerants and materials. Buy once and use it on any device signed into your Apple ID. Questions, feature requests, or a formula you'd like added? Let us know what would make your workday easier.