Hi All,
in regards to the last post I have known other cars have poor heater performance due to head gasket problems, this often manifests itself when the car is on idle but if you drive the car over 2500 rpm it the heater seems to be ok. try backflushing the heater core with a hose pipe and make sure the flow is about the same coming out as going in. after that refill the cooling system and run up the engine to temp and check that both heater hoses are hot.

CheeRS, Mike