This started last winter. I'll start my truck, I'll let it run to warm up, the gauge will say that the motor is warm, but the heat only blows ice cold air. When I finally get driving, after a few minutes, the air heats up and gets nice and hot, but I would prefer to be able to defrost my windows BEFORE I start driving.

It's an '06 xterra, "off road"

Thanks in advance!

Sounds like youre low on radiator fluid.

Nope, levels seem normal

Thermostat going bad possibly

Agreed...
If the T-stat is open slightly or weak the temp will read right but there is not enough restriction to force coolant into the heater core during warm up.
path of least restriction ya da ya da...
easier to flow through a 2 inch hose than a 5/8 inch hose...
so once is warm and you stop at a light does the heat get cooler a bit at idle.??
that would also be a sign of a T-stat as well.

It would seem that that may be the case. Lucky for me, they're not that expensive. I'll try it this weekend and see if it makes a difference

Did changing the thermostat fix the issue? I've noticed the same issue with my 13'...gauge says I'm at temp, just getting started in the morning...the minute I stop at a red light, the icicles start forming. Once I'm on the highway and the "whole truck" is up to temp the problem seems to go away and I can't even have the heat on at all (super hot). First thing I did was check the coolant level - right where it's supposed to be - even asked the tech when I went in for an oil change and he agreed it's where it was supposed to be...

I only have 20K on mine and thought it would be too soon for a T-stat malfunction...heard others says it's a pretty standard complaint with Nissans...any thoughts?

Have it checked. No need to be chilly.

sometimes the frontiers will get a bubble in the heater core. im guessing the X's are the same.

check the coolant level in the overflow. fill as needed. park with the front of the X facing uphill. let it cool. turn the truck on. run the HVAC through its settings for a few minutes. this should circulate coolant through the heater core and burp out any bubbles into the radiator. as the X heats up it should pressurise the radiator and push the air into the overflow. once its up to pressure i like to open the overflow cap to force the bubble into the overflow. (be careful coolant is hot!) refill as needed.

its worth trying this before you take it somewhere.

Cool idea.

As it turned out, I did need to top off my coolant. It did help a bit, but not a lot. I'll check again and see if any air bubbles out of the system. I did wind up buying a t-stat as it wasn't terribly expensive, just in case. Maybe I'll be returning it back to auto zone lol

There should be a T fitting on the heater hose at the fire wall. Put a hose on the fitting and put into the tank, this will take the air out of the system.