Heat and vent smells like coolant

When I turn the heat or the vent on I smell coolant blowing into the car. The previous owner said the cooling system was recently flushed and all new fluid was added. The level in the tank is ok. He also told me the heat doesn't work great which is why I turned it on. My first thought was to get a new thermostat and flush the system again since I'm not sure if it was properly flushed or just drained and re-filled. If I smell coolant in the car that means there's a leak somewhere right? Most likely in the heater core?

Heater core needs replacing.

Tom

That's what I thought. Thanks.