There are quite a few possible causes for your problem, from low coolant levels, blend door problems, heater control switch issues, thermostat stuck open (does your engine temp run below 190 F even after the engine has been running and in use for 15 minutes or more) all the way up to a plugged heater core.
I understand not wanting to go to the dealer, and I agree. A great many dealers are not trustworthy. The good thing about heating problems is pretty much any good shop can do those kinds of diagnostics and repair. I presume you have had vehicles previously, do you have a good independent garage that you deal with. If so, take it to them. If not, talk to your friends and neighbours and find out who they use and are happy with as an independent garage.
Tron - we were posting at same time I see.