No matter the system’s design, capacity, or energy source, a few standard practices should always be followed when bringing a heat transfer system online or taking it offline. Sticking to these steps helps extend the lifespan of the fluid and reduces the likelihood of thermal degradation.

System Startup

At room temperature, fluid viscosity can exceed 100 cSt. In colder outdoor conditions, below 0°C (32°F), viscosity may climb to 1000 cSt or more.

Although fluid can still be pumped at these levels, it’s not yet ready for full heating. Both small electric units and larger gas-fired heaters can deliver full power at startup, but the fluid’s thickness prevents efficient turbulent flow. If a heater is allowed to run at full output during this stage, overheating and thermal cracking of the fluid is highly likely. Essentially, the fluid moves too slowly across the heater, creating damaging hot spots.

Completely avoiding this risk may not always be possible, but there are measures that can help minimize fluid damage. Many electric systems feature controllers with soft-start settings that allow gradual heating. Similarly, gas-fired boilers often include a low-fire startup option. Your equipment manufacturer can provide recommendations on the best startup parameters for your system.

If these options are unavailable, raise the temperature in gradual increments of 10°C–15°C (20°F–30°F). This ensures smooth heating and prevents the fluid from overheating or breaking down. Always consult your equipment supplier for guidance on startup best practices.

System Shutdown

A few simple steps during shutdown can help protect your thermal fluid from unintended overheating.

During normal use, the heat source cycles between low and high fire, or on and off, to maintain the target temperature. It’s worth noting that heater chambers—boiler tubes or electric elements—can quickly become almost as hot as the heat source itself. This means that if circulation stops suddenly, the fluid may be exposed to heat levels far beyond its safe operating limit.

If the system is powered down without first allowing the heater and nearby components to cool while circulation continues, the fluid may remain trapped in the heater and “burn” or degrade thermally. To prevent this, always let the fluid cool to below 121°C (250°F) before shutting off the pumps. Using a heat exchanger or keeping the heater’s blower fan running can help speed the cooling process.