I've replaced the timing belt, water pump, and all hoses. But my car is only blowing cold air inside. The heat was working fine until the heater core hose burst.

Maybe something clogged the heater core, causing that hose to burst, either that or it's not getting hot water to it. If you can safely, no sleeves, with engine running and heat on full blast hold each hose, supply and return one with each hand. Both should be warm, if one is warm and the other not, then there is no circulation through core. If you know for fact it has supply, the core is clogged.

which heater hose burst.if its the hose mounted on the cylinder head under the distributor then the hose could have possibly burst do to oil leaking from the distributor o-ring and swelling the hose. there's also a heater control valve mounted on the heater hose if the cable is not attached or if the valve is not functioning properly it would not allow flow to the heater core and therefore no heat inside.