Re: no heat in middle of winter!!
Do you mean you can't get heat at the floor but the heater does work if you turn it on the dash vents? That sounds more like a fan problem, or a diverter problem in the ducting.
If your heat doesn't work at all, there is an easy thing you can do before you tear the dash out and replace the core. First, see if you can feel of the inlet and outlet hoses going through the firewall when the car is at operating temperature, is one of them cold? That is a clogged up core. I actually fixed my S10's clogged heater core by just pulling the hoses off and shooting water back through it with a water hose and blowing all the junk out of it (yay orange dexcool is super crap)