# HVAC Fan Affinity Laws Calculator

> HVAC Fan Affinity Laws 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 new airflow (CFM), static pressure, and shaft power after a fan speed change using the fan affinity laws (flow ∝ N, pressure ∝ N², power ∝ N³).

## Facts

- Endpoint: GET https://hvac-calc.x402tookit.com/fan-laws?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-fan-affinity-laws-calculator-34de7491
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_ChgwhGlJptJACtQHu8rIO

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-fan-affinity-laws-calculator-34de7491
```

Example prompt: My supply fan is currently running at 1200 RPM delivering 5000 CFM at 1.5 in. wg static pressure and consuming 3 hp — if I slow it down to 900 RPM with a VFD, what will the new airflow, pressure, and power be?

## When to prefer this

Use this endpoint when you need a fast, deterministic fan affinity law calculation given current and new fan speeds — ideal for VFD sizing, energy audits, commissioning checks, or any HVAC workflow where fan performance scaling is needed without running full simulation software.

## Known failure modes

- Missing required rpmFrom or rpmTo parameters returns an error
- Zero or negative RPM values may produce invalid ratios
- If optional cfm, staticPressureInWg, or power are omitted, corresponding new values will be null
- Extremely large speed ratios may produce physically unrealistic results without warning

## How this service works

Fan affinity laws: new airflow, pressure and power after a speed change (flow ~ N, pressure ~ N^2, power ~ N^3).

## Output

Returns the speed ratio (N2/N1), flow ratio, pressure ratio, and power ratio, along with computed new airflow (newCfm), new static pressure (newStaticPressureInWg), and new shaft power (newPower), plus a human-readable summary and any applicable disclaimer.

## 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": [
      "rpmFrom",
      "rpmTo"
     ],
     "properties": {
      "cfm": {
       "type": "number",
       "description": "Current airflow in CFM"
      },
      "power": {
       "type": "number",
       "description": "Current shaft power (hp or kW)"
      },
      "rpmTo": {
       "type": "number",
       "description": "New fan speed, same unit"
      },
      "rpmFrom": {
       "type": "number",
       "description": "Current fan speed (rpm or hertz)"
      },
      "staticPressureInWg": {
       "type": "number",
       "description": "Current static pressure in in. wg"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "asOf": {
       "type": [
        "null",
        "string"
       ]
      },
      "newCfm": {
       "type": [
        "null",
        "number"
       ]
      },
      "source": {
       "type": [
        "null",
        "string"
       ]
      },
      "reasons": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "summary": {
       "type": [
        "null",
        "string"
       ]
      },
      "verdict": {
       "type": [
        "null",
        "string"
       ]
      },
      "degraded": {
       "type": [
        "boolean",
        "null"
       ]
      },
      "newPower": {
       "type": [
        "null",
        "number"
       ]
      },
      "flowRatio": {
       "type": [
        "null",
        "number"
       ]
      },
      "disclaimer": {
       "type": [
        "null",
        "string"
       ]
      },
      "notChecked": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "powerRatio": {
       "type": [
        "null",
        "number"
       ]
      },
      "speedRatio": {
       "type": [
        "null",
        "n
… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/hvac-fan-affinity-laws-calculator-34de7491/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)