The nest cannot be always on because it is not provided with enough power. It has to use the power it has to charge an internal battery so they it can work at all. Always on would not have sufficient power.

I was talking about a switch for the HVAC fan, not the nest itself. With the nest you have to fiddle through a bunch of screens to turn the fan on and off. It is a personal pain point of mine.

Totally agree. I've been tinkering with my own project to do this. I wanted the recirc fan under programmable control as well to try and mix the house air once in a while and distribute the temperature a little better.

Nobody has ever offered this in a thermostat with the possible exception of the RadioThermostat CT30/3M50, which has a JSON API and lets you manually control the relays.

??? My 30 dollar third-world built brazilian crappy on-off thermostat has manual fan on and off. It can be programmed to turn on automatically when over/under a given temperature and also to not run for more than a predefined ammount of minutes.

As I understand it any temperature control designed for big refrigerators or freezers has this features. Some even allow you to pre-configure fan cycles (i.e. on for x minutes, off for y, repeat) and turn the cycle on or off depending on temperature or compressor state.

EcoBee thermostats give you the ability to set your fan to always on via the thermostat, API, and web interface.

This is my #1 gripe with The Nest.

Ahh Gotcha.

I'm curious as to why you want the physical switch rather than the ability to turn it to always on via software?

To me this is like the hardware mute switch on the side of the iPhone. Maybe let me decide with software what the switch does, but let me throw the switch when I want something NOW.