Agreeing with Hondo - A car heater works by blowing air over the heater matrix ( a seperate radiator filled with warm water from the engine coolant system )..
Hair dryer works by blowing cool air over an electrical filament.
Anyhow best to get Renault to check for obvious problems..
Would ask them to check heater control flaps working ok - heater fan - change and check for leaves pollen filter and heater intake feed pipes..
Failing that check the car
unit ( computer ) is not overheating due to a dusty of clogged cooling fan..
Any another tips on how you can repeat this smell ?
Have you any clip on air freshners on the heater vents ?
Mobile phone kits ?