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

instrument mechanism / verified-clean

# CFM ↔ Air Changes per Hour Converter mechanism

The inspectable method record for CFM ↔ Air Changes per Hour Converter, kept separate from implementation and qualification.

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

## Model scope

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.

- 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.

## Units and conventions

- 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.

## Inspectable vector

One of 4 source-bound review vectors:

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

## Failure boundary

**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.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/cfm-air-changes-per-hour-converter/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/cfm-air-changes-per-hour-converter/implementation/>)[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`

- `BOUNDARY_HAZARD_CATALOG.json`