I've just finally bitten the bullet and installed a Honeywell CM67
Programmable Room Stat in my hallway. I bought the version with Optimum
Start capability - which purports to decide for itself when to switch on the
heating in order to achieve the target temperature by the programmed start
time.

This seems to be working, but I'm curious to know what algorithm it uses in
order to decide when to turn on the heating. The literature doesn't make
this clear, so I wonder whether any of you actually know?

Several possibilities present themselves to me:
* it could assume a fixed (factory set) rate of rise of temperature, and
apply this to the current temperature in order to work out long long it will
take to get to the target temperature
* it could depend on one of the parameters - such as Proportional Band
Width - which can be set in the Installer Set-up Mode
* if it's *really* clever, it could calibrate itself by observing the actual
rate of temperature rise when the heating is on, and then apply this to its
future predictions

Does anyone out there know what it actually does?
--
Cheers,
Set Square
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