Why is my exhaust manifold overheating? 1993 Chevrolet Cavalier RS L4.?

I have a 1993 Chevy Cavalier RS. I just put a new battery in it today due to being dead and the car being out of commission for a year. I go o start it, it doesn't start, I give it a little gas and start it and starts right up then I let off the accel and it idles fine. I rev it for about 20 seconds and my mom and I see steam or smoke and I turn the car off really fast. The steam or smoke was coming from the exhaust manifold, It is scorching hot. I also replaced the heater core after this incident and I havent ran it since because I have work in the morning but I have been looking online and I am finding out it might be the head gasket........ Will the heater take care off this or is it the heater core, thermostat, or head gasket? And how do I find out? Without having to take it to a mechanic? and without taking anything apart IF POSSIBLE?