# HVAC Airflow & Load Calc

Airflow heat load, air changes, duct sizing, velocity, fan laws, efficiency conversions and mixed-air temperature.

## How to pay

Machine-payable over x402. USDC on: Base (eip155:8453), Solana (solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp), Polygon (eip155:137), Arbitrum One (eip155:42161).
No accounts. No API keys. No signup. The paying wallet is the account.

## Machine-readable

- OpenAPI: https://hvac-calc.x402tookit.com/openapi.json
- x402 manifest: https://hvac-calc.x402tookit.com/.well-known/x402
- Catalog (free): https://hvac-calc.x402tookit.com/catalog
- Health (free): https://hvac-calc.x402tookit.com/health
- Uptime (free): https://hvac-calc.x402tookit.com/uptime

## Endpoints (7)

### GET /air-changes — $0.02
Air changes per hour (ACH) from airflow and room volume, or the CFM needed for a target ACH.
Params: volumeCubicFeet?: number, lengthFt?: number, widthFt?: number, heightFt?: number, cfm?: number, ach?: number
Example: https://hvac-calc.x402tookit.com/air-changes?lengthFt=20&widthFt=10&heightFt=10&ach=10

### GET /duct-equivalent — $0.02
Equivalent round diameter of a rectangular duct (same friction), or the second side that matches a round duct.
Params: sideA: number, sideB?: number, roundDiameter?: number
Example: https://hvac-calc.x402tookit.com/duct-equivalent?sideA=12&sideB=8

### GET /duct-velocity — $0.02
Air velocity (FPM) and velocity pressure (in. wg) in a round or rectangular duct from CFM, or the CFM at a velocity.
Params: diameterIn?: number, widthIn?: number, heightIn?: number, cfm?: number, fpm?: number
Example: https://hvac-calc.x402tookit.com/duct-velocity?diameterIn=12&cfm=1000

### GET /efficiency-convert — $0.02
Convert EER, COP and kW per ton, and tons, BTU/h and kW of cooling capacity.
Params: eer?: number, cop?: number, kwPerTon?: number, tons?: number, btuh?: number, kw?: number
Example: https://hvac-calc.x402tookit.com/efficiency-convert?eer=12&tons=3

### GET /fan-laws — $0.02
Fan affinity laws: new airflow, pressure and power after a speed change (flow ~ N, pressure ~ N^2, power ~ N^3).
Params: rpmFrom: number, rpmTo: number, cfm?: number, staticPressureInWg?: number, power?: number
Example: https://hvac-calc.x402tookit.com/fan-laws?rpmFrom=1000&rpmTo=1200&cfm=1000&staticPressureInWg=1&power=2

### GET /mixed-air — $0.02
Mixed-air temperature of two airstreams (return plus outside air) and the outside-air fraction.
Params: cfmA: number, tempA: number, cfmB: number, tempB: number
Example: https://hvac-calc.x402tookit.com/mixed-air?cfmA=3000&tempA=75&cfmB=1000&tempB=95

### GET /sensible-heat — $0.02
Sensible heat from airflow and temperature difference (1.08 x CFM x dT), or the CFM needed for a heat load.
Params: deltaTF: number, cfm?: number, loadBtuh?: number
Example: https://hvac-calc.x402tookit.com/sensible-heat?cfm=1000&deltaTF=20

## Terms

Computed locally from standard HVAC rules of thumb and formulas, provided as is, with no warranty. Not a Manual J or other load calculation and not engineering advice; real systems need a qualified designer.