Heat Tracing Thermostats

Self regulating tape perhaps - plus a desire not to have the system defeated by meddling? (just a guess).

Otherwise it's common to have a local thermostat even with self regulating tape - just to make sure it's properly off when it's not needed.

  - Andy.

To avoid fiddling primarily. Also presuming outdoor installation, the thermostat is another opportunity for water to get in.

No LOCAL thermostats still allows control via a contactor in a switchroom, that is switched via an existing BMS system.

The title suggests heat tracing of pipes to prevent freezing of the contents, rather than space heating of rooms or areas within a building.

Local thermostatic control adds something else to go wrong and is best avoided due to the fiddle factor and water ingress to the connections.

Control of the whole trace heating installation by a contactor located indoors in the dry works better. Almost every BMS already has an external temperature sensor for optimised start of heating, or disabling of cooling.  This can be arranged to energise trace heating when conditions are cold enough to require this.