Heat transfer fluid

Heat transfer fluid is a fluid that carries heat from one part of a system to another. Heat transfer fluid is used in closed-loop systems. The fluid usually is a mixture of propylene glycol and water, or a heat-tolerant specialty oil. The anti-freezing fluid protects the system from freeze damage where low temperatures can cause freezing pipes, for example in the coldest season. The fluid may be, for example, a mixture of 50 percent propylene glycol and 50 percent water. Solutions also contain an inhibiting agent to prevent corrosion caused from the gradual breakdown of propylene glycol caused from high heat conditions during regular operation. The water/propylene glycol is effective to minus 28 degrees F (-50F non-bursting).

Ethylene glycol should not be used in hot water systems, because it is a poisonous health hazard if spills occur, or leaks allow the fluid to enter into the potable hot water system. Also, a water/ethylene glycol solution only protects from freezing to minus 33 degrees F --which is not as effective as propylene glycol's nonbursting -50°F performance.

In drainback systems, the fluid is usually distilled water mixed with a corrosion inhibitor. Drainback systems are a hybrid between draindown and closed-loop systems. Drainback systems do not need an antifreezing solution, because it depends on other aspects of system design to protect the system from freezing.