Not enough heat at idle when cold

[Iqoair]

When it's cold (-10c and below, especially -20+) I have little heat at idle. If it's -20c or below it's no heat at idle. Today ( -9c ) it was acceptable, however not great. When the RPM's are over 1000 it seems to pump it out ok. The engine coolant temp sits a little below the middle mark after it warms up (10-15 mins).

4wd works fine, the heater control vent options work fine. No coolant leaks, and the coolant level is at "min" when cold and hasn't budged. Lots of power and no other symptoms. 80,000 kms on the truck, 2006 F-350 6.0.

Suggestions?

[Diesel_Diagnostician]

Yeah, you have to work them to get the heat out of them. Heat pretty much dies off of my diesels (even my 1.9tdi) when im just idling, gotta love owning diesels in canada eh? But, if you do feel you have an issue (everything seems good by your write up though) it may be an issue with your vistronic fan clutch. My partner in crime had one come in that the fan clutch was constantly being comanded on (i believe he found a short to power or something like that). It took the customer forever to build any type of heat. Just throwing that idea out there.