Source: https://guthlabs.ai/docs/instruments/cfm-air-changes-per-hour-converter/implementation/

instrument implementation / implementation-contract

# CFM ↔ Air Changes per Hour Converter implementation

A source-bound implementation contract for CFM ↔ Air Changes per Hour Converter; deployment and executable qualification remain separate.

Status: **VERIFIED_CLEAN**Lifecycle: **implementation-contract**

## Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

**Record owner**: Guth Instruments

**Lifecycle**: verified-clean

**Evidence ID**: t5-155

**Effect**: Computation or source lookup only

## Input and validation requirements

A zero room volume causes division by zero and must be rejected. Negative CFM also exposes an unresolved sign convention: signed arithmetic returns negative ACH, whereas normal HVAC usage generally expects a nonnegative airflow magnitude.

## Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

## Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

````
{
  "inputs": {
    "mode": "ach_from_cfm",
    "cfm": 250,
    "room_volume_ft3": 15000
  },
  "expected_outputs": {
    "ach": 1
  },
  "working": "ACH = CFM × 60 / Volume = 250 × 60 / 15000 = 15000 / 15000 = 1 ACH."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/cfm-air-changes-per-hour-converter/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/cfm-air-changes-per-hour-converter/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/cfm-air-changes-per-hour-converter/qualification/>)

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json`

- `evidence-tranche5/tranche5-results.json`