My 05 sxt has a heater problem.
The fan blows for defroster and all vent settings.
I don't get any heat regardless of setting.
The fuse box is marked with sizes only no ID for what
each fuse is for.
Not sure if I should be looking for a fuse or a relay.
In either case, I need to know so I can check and
replace if necessary.
Any other info would be helpful.

 

the heater doesnt have fuse.
First thing I suggest you to check is coolant level. Open radiator cap when the car is cold, see if it is full. It not, fill it up, and look for leak.

If coolant is full, is the temperature on the gauge showing normal?
If both are check out ok, you might have Heater core or blend door problem, might need to go to a shop.