Hi Anonymous.
So, they replaced the radiator. And then the heater hose, plenum gasket, and throttle body gasket. I'm assuming you were talking about the radiator reservoir being almost empty, yes?
The heater is like a mini radiator stuck inside your dashboard. Coils, fins, engine coolant inside. And a valve that switches between circulating engine coolant through that little radiator, or bypassing it.
When the shop replaced the heater hose, I'd hope that they replaced both of them, unless there was some overt damage to just one of them. there need to be two hoses, one from the engine to the firewall (IN), and another back from firewall to engine (OUT). If you're not getting any heat right now (but able to blow air), then there isn't any coolant circulating into the small radiator. I don't know your specific car well enough to know if the valve is a manual one (a knob or lever with some tangible push-back when you move it between cool and hot), or a mechanical one, where you turn a control, and some small motor turns the valve.
The manual for your car is here:
http://www.kia.ca/content/ownership/ownersmanual/2004_sorento_Owners_Manual_EN.pdf There are both manual and automatic climate control options, I don't know which you have. I do note that there are several fuses/relays tied to functions like 'heater' and 'AC' You can see them on pages 6-10 and 6-11 (around page 218 of the manual. You may want to see if a blown fuse or bad relay might be the root of the problem.
If it is the heater core, that can tend to be a bit of a labor intensive operation since the core is inevitably at the deepest rear of the stuff behind the dashboard, right next to the firewall. Unless you're really eager to DIY, it may be worth the money to let a garage do it if that's the root. Start with checking the fuses.
Good Luck!
D