[sokoloff]

> What if it's leaking CO into your house

While I agree with your overall point, this clause is irrelevant to/not supportive of it. The presence of a thermostat wasn't going to help you here either and there are vastly more furnaces with connected thermostats than disconnected to worry about.

CO detectors and alarms are needed to address this risk.

[zdragnar]

Your thermostat is in a far less likely place to be overloaded with CO should the alarms start going off, though. If the thermostat is gone, you have to physically go to the furnace itself or shut off power at the circuit breaker.

Freezing water pipes are bad, but a furnace running non-stop is going to exceed its duty cycle and pose a greater hazard.

[sokoloff]

Whatever was implemented as this poorly-thought-through fail-safe would be implemented in the furnace itself, thus that furnace implementation could manage any safety-related concerns, though heating equipment is overwhelmingly rated to 100% duty cycle already. (My goal for my boiler is to have at least 22 hours per day of heating demand to ensure that I'm using the exact minimum temperature water to maintain temp in the house, to maximize efficiency.)

[Marsymars]

My furnace runs pretty close to non-stop when it’s below -30 outside, I imagine a bigger concern than duty cycles if it did that when it wasn’t -30 would be that it would still be pushing the indoor temperature to 50°C above the outdoor temp.