HVAC Pro Calculator · Works offline
HVAC calculator app that shows its work
HVAC calculator app for field techs: BTU load, duct sizing, NEC voltage drop, wire size, refrigerant P-T charts, superheat and subcooling. Works offline. Every formula cited. ASHRAE. NEC 310.16. SMACNA. No ads, no tracking.
ASHRAE
friction-rate duct equation
NEC 310.16
exact ampacity tables
SMACNA
duct construction standards
CoolProp
refrigerant saturation data
Free calculators · right here in the browser
Try the math before you install anything
Three of the app's calculators run on this site, free: the superheat & subcooling calculator for R-410A, R-454B, R-32 and R-22, a duct size calculator that works like a ductulator, and a CFM calculator for tonnage, temperature rise and air changes. Same formulas, same sources, no sign-up.
Superheat & Subcooling Calculator
Gauge pressure and line temperature in, superheat or subcooling out, with a verdict against the target. R-410A, R-454B, R-32, R-22. Target superheat for fixed-orifice systems too.
Open the calculator → Free · runs in your browserDuct Size Calculator
Round or rectangular duct size for any airflow and friction rate, with the velocity check that tells you if it will be noisy.
Open the calculator → Free · runs in your browserCFM Calculator
Airflow from tonnage, from furnace temperature rise, or from room air changes — the three ways techs actually need CFM.
Open the calculator →Commercial HVAC calculator checks
Use these tools for individual airflow, duct-size and refrigerant checks on a commercial job. Enter the equipment's airflow and pressure readings; residential CFM-per-ton and velocity defaults do not replace the project design, equipment data or a full commercial load calculation.
Sheet metal work in HVAC Pro Calculator
For duct dimensions, the free duct size calculator checks round and rectangular duct against airflow and friction rate. The app's Sheet Metal function uses offset rise and run to calculate diagonal length and angle. It does not produce a full fabrication pattern or check metal gauge, seam allowances or reinforcement. Check current app access in the listing and in-app offer.
Calculator features · check current app access
Prove it on your next service call
Duct sizing is listed as a Pro feature. See the App Store and in-app offer for current access, plans and eligibility.
BTU & Cooling Load
Heat and cool sizing from square footage, ceiling height, climate zone, occupancy, and sun exposure. ASHRAE-derived rules of thumb.
Duct Sizing
ASHRAE friction-rate equation, Manual D simplified. Round and rectangular, equivalent-diameter solver, velocity check with noise warnings.
Unit Converter
Every unit the trade touches — BTU, kW, tons, CFM, L/s, °F/°C, psi, kPa, in wc. Imperial default, metric one tap away.
PlateScan · Pro
Stop retyping faded data plates
Point the camera at the unit's data plate — or just type the model number. PlateScan decodes nominal tonnage and refrigerant from the manufacturer's model nomenclature (Trane, Goodman, York, Rheem, Lennox, Carrier and family) and autofills the right calculator. Fully offline. You confirm every value before it's used — it's a typing-saver, not a guess.
- → Model & serial decode for the major brands
- → Autofills refrigerant type and nominal tons → CFM
- → Works with no signal — rooftop, basement, crawlspace
More app features · check the current in-app offer
The rest of the truck
Voltage Drop & Wire Size
NEC voltage-drop method tied to exact NEC Table 310.16 ampacity — not approximations. 3%/5% checks built in.
Refrigerant P-T Charts
R-410A, R-32, R-454B, R-22. CoolProp-backed saturation data with bubble/dew handling for blends.
Superheat & Subcooling
Enter pressures and line temps, get charge diagnostics with the target ranges for TXV and fixed-orifice systems.
Sheet Metal Offset
Enter offset rise and run for the diagonal length and angle. Layout math only; verify material, seams and reinforcement against the job requirements.
PlateScan
Point the camera at the data plate — or type the model — and it decodes tonnage and refrigerant, then autofills the right calculator. Offline.
Saved Jobs + iCloud
Name and save a calculation. The app attempts private iCloud sync when available; check the job on your other device before relying on it.
Branded PDF Export
Job name, inputs, result, and the standard cited for the formula — ready to hand to a customer or attach to a submittal.
Three taps to a cited answer
01
Pick the calculator
BTU load, duct, voltage drop, P-T, superheat — the grid is one screen, gloves-friendly.
02
Enter what you measured
Pressures, line temps, square footage, run length. Every input has its unit right there.
03
Read the result + the source
"BTU load: 28,800. Source: ACCA Manual J Simplified." The formula's standard is printed under every result.
Field guides
The reference shelf
The calcs behind the calculators — superheat, PT charts, duct sizing, NEC wire sizing — written the way a senior tech would explain them.
Checking charge? Start with the R-454B PT chart, how to calculate superheat, and what your subcooling should be. For airflow, read CFM per ton before choosing duct size for a 3-ton AC unit. For a condenser circuit, use the nameplate when checking wire size for an AC condenser.
New to gauge tables? Learn to read a P-T chart, then use the R-32 pressure-temperature table for single-component readings. Before changing charge, check which reading a TXV system needs. For a long electrical run, separate the 3-ton breaker's nameplate limit from the voltage lost along the conductor.
How to Calculate Superheat
The formula, where to clamp, and target ranges for fixed-orifice and TXV systems.
Read the guide → RefrigerantR-454B PT Chart
Full pressure-temperature table with bubble and dew columns, plus how glide changes your readings.
Read the guide → Airflow & DuctsCFM Per Ton: The 400 Rule
400 CFM/ton standard air — when to run 350 in humid climates and 450 in dry ones.
Read the guide → Airflow & DuctsWhat Size Duct for a 3-Ton Unit?
Trunk and return sizes at 1,200 CFM, round-to-rectangular equivalents, and velocity limits.
Read the guide → ElectricalWhat Size Wire for an AC Condenser?
Size off the nameplate MCA — not tonnage — with NEC 310.16 and 10/2 vs 10/3 explained.
Read the guide → ElectricalWhat Size Breaker for a 3-Ton AC?
MOCP vs MCA off the nameplate, typical 30–45A range, and the oversized-breaker red flag.
Read the guide →Match the chart to the job
Read the R-410A pressure-temperature chart or R-22 pressure-temperature chart before entering a gauge reading. For airflow checks, work through total external static pressure with the unit’s own test points and rated limit.
The math, already on your phone
Duct sizing is listed as a Pro feature. See the App Store and in-app offer for current access, plans and eligibility.