# HVAC Duct Equivalent Round Diameter Calculator

> HVAC Duct Equivalent Round Diameter 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 the equivalent round duct diameter for a rectangular duct (same friction loss), or finds the missing rectangular side that matches a given round duct diameter.

## Facts

- Endpoint: GET https://hvac-calc.x402tookit.com/duct-equivalent?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-equivalent-round-diameter-calculator-d50e3266
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_8o0jGXFQLtQuSnS1WGveB

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-equivalent-round-diameter-calculator-d50e3266
```

Example prompt: What's the equivalent round duct diameter for a rectangular duct that's 16 inches wide and 10 inches tall? I need to find the round size with the same friction loss.

## When to prefer this

Use this endpoint when you need to size round or rectangular HVAC ducts to have equivalent friction loss — particularly when retrofitting between duct shapes, selecting fittings, or performing duct layout design. It is purpose-built for the HVAC equivalent round diameter formula, making it more reliable and accurate than a general-purpose calculator or LLM arithmetic.

## Known failure modes

- Missing required sideA parameter returns an error
- If neither sideB nor roundDiameter is provided, the calculation cannot resolve both unknowns
- Non-numeric or negative input values may return validation errors
- Service may return a degraded flag if partial results are available
- Network or payment-related failures (402 payment required if USDC not provided)

## How this service works

Equivalent round diameter of a rectangular duct (same friction), or the second side that matches a round duct.

## Output

Returns the equivalent round diameter for the given rectangular duct dimensions (or the missing rectangular side), along with aspect ratio, rectangular cross-sectional area, round cross-sectional area, and a text summary. May include a disclaimer and degraded/error flags.

## 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": [
      "sideA"
     ],
     "properties": {
      "sideA": {
       "type": "number",
       "description": "One side of the rectangular duct (inches or any unit)"
      },
      "sideB": {
       "type": "number",
       "description": "Other side, same unit; send this or roundDiameter"
      },
      "roundDiameter": {
       "type": "number",
       "description": "Round duct diameter to find the matching second side"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "asOf": {
       "type": [
        "null",
        "string"
       ]
      },
      "sideA": {
       "type": [
        "null",
        "number"
       ]
      },
      "sideB": {
       "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"
       ]
      },
      "roundArea": {
       "type": [
        "null",
        "number"
       ]
      },
      "disclaimer": {
       "type": [
        "null",
        "string"
       ]
      },
      "notChecked": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "aspectRatio": {
       "type": [
        "null",
        "number"
       ]
      },
      "rectangularArea": {
       "type": [
        "null",
        "number"
       ]
      },
      "equivalentRoundDiameter": {
       "type": [
        "null",
        "number"
       ]
      }
     }
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/hvac-duct-equivalent-round-diameter-calculator-d50e3266/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)