CFM ↔ Air Changes per Hour Converter mechanism

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

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