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

instrument / verified-clean

# CFM ↔ Air Changes per Hour Converter

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Inspectable records

[01**Overview**Purpose and lifecycle](<https://guthlabs.ai/docs/instruments/cfm-air-changes-per-hour-converter/>)[02**Mechanism**Method and assumptions](<https://guthlabs.ai/docs/instruments/cfm-air-changes-per-hour-converter/mechanism/>)[03**Implementation**Binding and validation](<https://guthlabs.ai/docs/instruments/cfm-air-changes-per-hour-converter/implementation/>)[04**Qualification**Evidence and errata](<https://guthlabs.ai/docs/instruments/cfm-air-changes-per-hour-converter/qualification/>)

## Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

**Area**: Mechanical, Civil & Structural Engineering — Statics/Dynamics, Strength of Materials, Machine Design, Civil, HVAC, Vibration

**Tranche**: tranche-5

**Evidence ID**: t5-155

**Ledger rows**: 1

No ledger note is attached.

## Review findings

The ACH formula is standard under the stated imperial-unit assumptions, but the catalog claim is bidirectional while only the forward formula is supplied. The honest label should explicitly state the supported directions, CFM, cubic feet, and ACH units.

### Formula and scope findings

- The supplied formula ACH=CFM×60/Volume(ft³) is correct only for calculating ACH when airflow is in CFM and volume is in cubic feet.

- The instrument claims conversion in both directions, but the required inverse formula CFM=ACH×Volume(ft³)/60 is missing.

- The input and output modes are not explicitly defined, so it is unclear whether a given numeric airflow value is CFM or an ACH target.

### Unit assumptions

- CFM means cubic feet per minute.

- Room volume must be expressed in cubic feet for the supplied formula.

- The factor 60 converts minutes to hours.

- ACH is expressed as air changes per hour.

- Metric volumes such as cubic metres must be converted to cubic feet before using the supplied formula.

## Boundary hardening

**BREAK_CLAIMED** · SELF_FLAGGED

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.

## Errata and corrections

No applied erratum is attached to this unique-name record.

## Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

````
{
  "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."
}
````

## Related workflows

No source-defined multi-instrument workflow membership is recorded.

## Sources and evidence

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

- `VERIFIED_LEDGER.json · VERIFIED_CLEAN`

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

- `BOUNDARY_HAZARD_CATALOG.json`