# HVAC Duct Velocity & Velocity Pressure Calculator

> HVAC Duct Velocity & Velocity Pressure Calculator is a paid API for AI agents from hvac-calc.x402tookit.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-29).

Calculates air velocity (FPM) and velocity pressure (in. wg) in a round or rectangular duct from CFM, or the CFM required to achieve a given velocity.

## Facts

- Endpoint: GET https://hvac-calc.x402tookit.com/duct-velocity?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-29
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/hvac-duct-velocity-velocity-pressure-calculator-b30fd5d3
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_U8iotP7lWCu8YH1WWIeua

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability hvac-duct-velocity-velocity-pressure-calculator-b30fd5d3
```

Example prompt: What's the air velocity and velocity pressure in a 10-inch round duct carrying 600 CFM?

## When to prefer this

Use this endpoint when you need to compute duct air velocity (FPM) or velocity pressure (in. wg) from a known airflow rate and duct geometry, or reverse-calculate CFM from a target velocity — specifically for round or rectangular ducts in HVAC design, commissioning, or troubleshooting contexts.

## Known failure modes

- Missing both cfm and fpm — must provide at least one
- Missing both diameterIn and widthIn/heightIn — duct dimensions required
- Non-positive or zero values for dimensions may produce errors
- Rectangular duct requires both widthIn and heightIn together
- Very large or unrealistic values may return warnings or degrade gracefully

## How this service works

Air velocity (FPM) and velocity pressure (in. wg) in a round or rectangular duct from CFM, or the CFM at a velocity.

## Output

Returns calculated air velocity in FPM, velocity pressure in inches water gauge (in. wg), duct cross-sectional area in both square inches and square feet, and the input CFM or FPM (whichever was derived). Also includes a summary, disclaimer, and data timestamp.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [],
     "properties": {
      "cfm": {
       "type": "number",
       "description": "Airflow in CFM to get the velocity; send this or fpm"
      },
      "fpm": {
       "type": "number",
       "description": "Velocity in feet per minute to get the CFM"
      },
      "widthIn": {
       "type": "number",
       "description": "Rectangular duct width in inches"
      },
      "heightIn": {
       "type": "number",
       "description": "Rectangular duct height in inches"
      },
      "diameterIn": {
       "type": "number",
       "description": "Round duct diameter in inches; or send widthIn and heightIn"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "cfm": {
       "type": [
        "null",
        "number"
       ]
      },
      "fpm": {
       "type": [
        "null",
        "number"
       ]
      },
      "asOf": {
       "type": [
        "null",
        "string"
       ]
      },
      "source": {
       "type": [
        "null",
        "string"
       ]
      },
      "reasons": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "summary": {
       "type": [
        "null",
        "string"
       ]
      },
      "verdict": {
       "type": [
        "null",
        "string"
       ]
      },
      "degraded": {
       "type": [
        "boolean",
        "null"
       ]
      },
      "disclaimer": {
       "type": [
        "null",
        "string"
       ]
      },
      "notChecked": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "areaSquareFeet": {
       "type": [
        "null",
        "number"
       ]
      },
      "areaSquareInches": {
       "type": [
        "null",
        "number"
       ]
      },
      "velocityPressureInWg":
… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/hvac-duct-velocity-velocity-pressure-calculator-b30fd5d3/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from hvac-calc.x402tookit.com](https://www.zero.xyz/host/hvac-calc.x402tookit.com/llms.txt)