When I turn on the heater in the morning it takes ahalf hour before it blows warm air. Once it starts it blows warm air all day.
Any thoughts?

Dying Heater Core?

is this a problem with an RX-8 or some other car? whichever it is tell us the car the model year whether its new or used and how many miles

Your cold/heater turn nob is stuck, the control board behind is acting up. Have the heater nob turned all the way to heat and then flick it quickly to the cold side. You may have to do it once or twice to get the control board behind the knob to recognize the difference. You should notice the warm air turn to cool air.

There are plenty of threads on this subject matter. One, you can pay close to 400 dollars for a new control board or you can flick your knob from hot to cold several times until cool air comes out of it.

Also you have to remember , warm air is not going to come out of any car , especially if its cold, or if you live up north where the temps are freezing and below.

I live in Fl where the temps are in the low 70's now, and my car won't blow warm air out of it until its fully warmed up.