My heat sucks

it can only be two things.....

1. there is no/not enough coolant flow thru the heater core. think of it as a mini radiator. with engine running and engine at temp both hoses should be warm/hot to the touch. squeeze the outlet house coming from the fire wall. you should feel coolant flowing thru. it its slow flowing or not at all you can disconnect both hoses from engine and flush the core itself with the garden hose. it should flow freely. if no flow or very little flow then its time to replace it.

2. the flapper in the heater box is not in the correct location. it either pulls air from the cowl vent directly into the passenger compartment or it pulls the air thru the heater core into the passenger compartment. that is what heats the air. you can look under the dash and follow the cables from heater controls to the flaps on the heater box. alot of times the ends break off.