Glossary · Testing & air leaks
ppm (parts per million)
Also called: ppb · parts per billion
A way to express tiny concentrations: 1 ppm is one part of a gas in a million parts of air, used for carbon monoxide readings.
What it means
Gas detectors report carbon monoxide (CO) and some other indoor pollutants in ppm; ppb (parts per billion) is a thousand times smaller and is used for gases like formaldehyde. Because the numbers are small, what matters is comparing a reading with a guideline and how long the exposure lasts.
Why it matters in an audit
Knowing the unit lets you read a CO meter or air quality report and tell a normal reading from a dangerous one.
Typical numbers
Reference values with their sources. Your energy advisor’s report gives the figure for your own house.
| What | Value | Source |
|---|---|---|
| Scale | 10 ppm = 0.001% of the air; 1 ppm = 1,000 ppb | Arithmetic |
| Health Canada CO guideline (24-hour average) | 10 ppm | canada.ca ↗ |
| Health Canada formaldehyde guideline (8-hour average) | 40 ppb (50 µg/m³) | canada.ca ↗ |