Temperature Conversion Chart
Fahrenheit to Celsius from −40 °F (where the scales cross) to 250 °F (steam and high-limit territory), in 5° steps through the working range. The temperatures HVAC design actually revolves around — chilled water, supply air, setpoint, DHW, boiler supply — are marked on their rows, so the chart doubles as a design-point reference.
°F → °C, −40 to 250
| °F | °C | HVAC design point |
|---|---|---|
| -40 | -40 | — |
| -35 | -37.2 | — |
| -30 | -34.4 | — |
| -25 | -31.7 | — |
| -20 | -28.9 | — |
| -15 | -26.1 | — |
| -10 | -23.3 | — |
| -5 | -20.6 | — |
| 0 | -17.8 | — |
| 5 | -15 | — |
| 10 | -12.2 | — |
| 15 | -9.4 | — |
| 20 | -6.7 | — |
| 25 | -3.9 | — |
| 30 | -1.1 | — |
| 32 | 0 | Freezing point of water |
| 35 | 1.7 | — |
| 40 | 4.4 | Chilled-water supply (typical) |
| 45 | 7.2 | — |
| 50 | 10 | — |
| 55 | 12.8 | Cooling supply air (typical) |
| 60 | 15.6 | — |
| 65 | 18.3 | — |
| 70 | 21.1 | — |
| 75 | 23.9 | Indoor design / room setpoint |
| 80 | 26.7 | — |
| 85 | 29.4 | — |
| 90 | 32.2 | — |
| 95 | 35 | Summer outdoor design (hot climates) |
| 100 | 37.8 | — |
| 105 | 40.6 | Heating supply air (heat pump, typical) |
| 110 | 43.3 | — |
| 120 | 48.9 | — |
| 130 | 54.4 | — |
| 140 | 60 | DHW storage / scald-risk threshold |
| 150 | 65.6 | — |
| 160 | 71.1 | — |
| 170 | 76.7 | — |
| 180 | 82.2 | Hydronic boiler supply (typical) |
| 190 | 87.8 | — |
| 200 | 93.3 | — |
| 210 | 98.9 | — |
| 220 | 104.4 | — |
| 230 | 110 | — |
| 240 | 115.6 | — |
| 250 | 121.1 | — |
Reading the marked rows
The design points are marked because they are where °F/°C confusion actually costs money — a European submittal listing 7 °C chilled water is the same 44–45 °F loop an American spec calls out, and 12.8 °C supply air is the familiar 55 °F. The two typical-value pairs worth memorizing: 75 °F / 23.9 °C for space setpoint and 55 °F / 12.8 °C for cooling supply air.
For the refrigerant side of the temperature story, the R-410A and R-454B pressure-temperature charts work in saturation temperatures, and the psychrometric reference covers wet-bulb and dew point.
Common questions
What is the formula to convert Fahrenheit to Celsius?
°C = (°F − 32) ÷ 1.8, and back the other way °F = °C × 1.8 + 32. The 32 is the freezing-point offset and the 1.8 is the size ratio of the degrees — a Celsius degree is 1.8 times larger than a Fahrenheit degree. The conversion is exact, not an approximation.
At what temperature are Fahrenheit and Celsius equal?
At −40°. It is the one point where the two scales cross: −40 °F = −40 °C, which is why this chart starts there. It also happens to be a common low-ambient design rating for equipment.
What are the standard HVAC design temperatures?
The marked rows are the ones the trade designs around: 44 °F-class chilled-water supply (40–45 °F), 55 °F cooling supply air, 75 °F indoor setpoint, 95 °F hot-climate outdoor design, 105 °F heat-pump heating supply, 140 °F hot-water storage, and 180 °F hydronic boiler supply. All except freezing (32 °F) are conventions or typical values — your plans and local code govern.