Specific Heat of 30 % Propylene Glycol
| Value | 3,850 J/(kg·K) |
| Status | Measured: ± 150 J/(kg·K) (0.039 relative) |
| Source | ASHRAE Handbook of Fundamentals, Ch. 31 (Secondary Coolants) |
| Categories | Material PropertiesEngineering & Trade |
| joule per kilogram-kelvin | 3,850 J/(kg·K) |
| joule per kilogram-Celsius | 3,850 J/(kg·°C) |
| foot pound-force per pound-Rankine | 715.57076 ft·lbf/(lb·°R) |
| kilojoule per kilogram-kelvin | 3.85 kJ/(kg·K) |
| kilojoule per kilogram-Celsius | 3.85 kJ/(kg·°C) |
| joule per gram-kelvin | 3.85 J/(g·K) |
| calorie per gram-Celsius | 0.92017208 cal/(g·°C) |
| kilocalorie per kilogram-Celsius | 0.92017208 kcal/(kg·°C) |
| BTU per pound-Fahrenheit | 0.9195567 BTU/(lb·°F) |
| BTU per pound-Rankine | 0.9195567 BTU/(lb·°R) |
Propylene glycol, 30 % by volume at any temperature
-10 to 100 °CThe value above is one point on this curve. A 30 % by volume propylene glycol solution, freeze protection to about −13 °C — the usual charge for a snowmelt or make-up air loop that only has to survive a Canadian shoulder season.
Learning zone
Glycol costs you three ways at once, and only the first is obvious. Specific heat drops (30 % PG is about 3850 J/(kg·K), 50 % PG about 3600), density rises slightly, and viscosity climbs steeply at low temperature — a 50 % mix at 0 °C is roughly four times as viscous as water. The net effect on a hydronic loop is that you need 10–20 % more flow for the same heat rate, at a higher pump head, through a coil with a lower film coefficient.
Rules of thumb that survive: derate coil and heat-exchanger capacity by roughly 5 % for 30 % glycol and 10–15 % for 50 %, and increase pump flow correspondingly. Propylene glycol is the food-safe, less toxic choice and is standard in HVAC and potable-adjacent systems; ethylene glycol transfers heat somewhat better and is used where toxicity is acceptable. Inhibited industrial glycol is not automotive antifreeze — the silicate and phosphate packages differ, and automotive coolant in a hydronic loop will foul plate exchangers. Concentration must also be verified by refractometer at the system, since installers routinely mix by guess.