HVACopediaPressure & vacuum tables
Vacuum, psi and kPa tables, water boiling point, altitude, refrigerant pressures in every unit.
Vacuum conversion
| Vacuum (in. Hg) | Absolute (mm Hg) | Absolute (psia) | Water column (ft) |
|---|---|---|---|
| 29.92 (atmosphere) | 760 | 14.7 | 33.4 |
| 28 | 711 | 14 | 32.2 |
| 26 | 660 | 13 | 29.9 |
| 24 | 610 | 12 | 27.6 |
| 22 | 559 | 11 | 25.3 |
| 20 | 508 | 10 | 23.0 |
| 18 | 457 | 9 | 20.7 |
| 16 | 408 | 8 | 18.4 |
| 14 | 356 | 7 | 16.1 |
| 12 | 305 | 6 | 13.8 |
| 10 | 254 | 5 | 11.5 |
| 8 | 203 | 4 | 9.2 |
| 6 | 152 | 3 | 6.9 |
| 4 | 102 | 2 | 4.6 |
| 2 | 51 | 1 | 2.3 |
| 0 | 0 | 0 | 0 |
Atmosphere = 29.92 in. Hg = 14.7 psia = 760 mm Hg = 760,000 microns. 1 in. Hg = 25.4 mm Hg = 25,400 microns.
psia, psig and kPa
| psia | psig | kPa (absolute) |
|---|---|---|
| 105 | 90 | 725 |
| 90 | 75 | 621 |
| 75 | 60 | 518 |
| 60 | 45 | 414 |
| 45 | 30 | 311 |
| 30 | 15 | 207 |
| 15 | 0 | 100 |
| 10 | −5 | 69 |
| 5 | −10 | 35 |
| 0 | −15 | 0 |
psia = psig + 14.7 at sea level (15 is a common shortcut). Use absolute pressure for gas-law math.
Water boiling point under vacuum
| Water temp (°F) | Vacuum (in. Hg) | Microns |
|---|---|---|
| 35 | 29.72 | 5,170 |
| 45 | 29.62 | 7,630 |
| 55 | 29.48 | 11,075 |
| 65 | 29.30 | 15,815 |
| 75 | 29.05 | 22,245 |
| 85 | 28.70 | 30,850 |
| 95 | 28.25 | 42,220 |
| 105 | 27.68 | 57,050 |
| 115 | 26.92 | 76,180 |
| 125 | 25.96 | 100,590 |
This is why a deep vacuum dries a system. Water at room temperature boils off at a few thousand microns.
Atmospheric pressure by elevation
| Elevation (ft) | Atmosphere (psia) |
|---|---|
| Sea level | 14.7 |
| 2,000 | 13.7 |
| 4,000 | 12.9 |
| 5,000 | 12.2 |
Re-zero an analog gauge open to the air at the job elevation. Never adjust an absolute gauge.
Refrigerant pressure in every unit
Pick a refrigerant to see its pressure in every unit.
Take it with you
All of these tables, plus the calculators, are in the HVACopedia app, offline.
Calculation aids and reference figures for licensed technicians. Always follow the manufacturer’s data plate and manual for the exact model, and local codes. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Pressures are typical saturation values and change with load and airflow.