I have just had electric radiant floor heating installed as a supplemental heat source in a cold, north facing room.  I've been using air temp setting and running it at 74 degrees when I'm in the room (which is comfortable) but turning it down to 67-68 when I'm not using that room.  The forced air furnace is set at 69 degrees.

1.  Should I be turning it completely off at night - or is turning it down a better choice?  If I should turn it down, is an 8-9 degree reduction appropriate? 
2.  Or should I set it at my preferred comfort level and just leave it - seems like this is wasteful of energy, warming it when no one is home.
3.  Should I be using floor temp rather than air temp since this is supplemental heat?

Any suggestions would be appreciated - my installer really gave me no good suggestions on the best way to use this and the thermostat instructions really don't give any guidance on this topic either.

As supplimental heat, it should be turned on and used as what it was designed for. Since you've stated that it's strictly supplimental and not as floor warming, set the tstat to come on at an appropriate time to give the floor a chance to warm up dependant on the time it takes to warm up. The deeper the element is in the floor coupled with the wider the temperature range from turn down (off) to the set point, the longer the time it will take for you to get a response from it.

It has always been a strange concept to me, as a electric radiant heat installer, that clients will sometimes install radiant heat to take the cold out of the floor (as compared to primary heat), which is a luxury in and of itself, yet not want to turn it on because it's a waste of energy. In the correct application, electric in-floor radiant is the most efficient form of heat on the market. You get a dollars' worth of heat for the dollar you spend. Give or take .3%. No other form of heat can claim that.

Huh? Are we going to do this again?

Hi,

I manufacture Radiant floor warming and ceiling heating. Did you purchase a floor programmable thermostat? If you had you would be able to program the floor 4 times a day 7 days a week so that it is not running while you are away from home. I would turn it on at least 1 hour before your arrival home and you should have a nice warm floor when you arrive home.

www.calorique.com