2000 Kia Sephia Heater?

Have you check the coolant level in the radiator, and reservoir?

Low coolant level will cause this problem. Amongst others....

You may have a bad thermostat. Check the coolant level in the radiator by removing the cap when the engine is cold of course. There are a pair of heater hoses from the firewall to the engine should be on the passenger side it's the same system as any other car. You need to see if the upper and lower radiator hoses are the same or different temperature this could tell you if the thermostat is opening. You could have a clogged heater core you could run some flush threw the system.

Well...your best bet is to determine if you're losing coolant or not. If you're losing coolant then it's likely a leak at the heater core (or anywhere...in the system...but that's a likely location where a small leak would occur). If you're NOT losing coolant then it means there's a clog in the system somewhere before the coolant enters the heater core. The heat you get in the interior is air blown off the heater core.

As far as finding them...your best bet it to locate the RADIATOR behind your front bumper (usually a red cap up top) and trace the lines going into the unit and out of the unit.

question as to the timing belt I am having a similar prob however mine broke my brother decided to drive it long distance when I told him not to and the damn thing snapped off I need to replace it but as far as I can tell the only thing that's is the belt about how much is this gonna run me as im not a mechanic however I have a budy whos a mechanic telling me if I buy the part hed do it for 20 however as im not truly sure if that's all that's wrong with it im curious as what I should do I don't want to fix something only to find out that something else is broken as well and the mechanics where im at refuse to work on it as its a 2000 model and not new ?