Use power over voltage calculation.
Power= 4kW or 4000watts
Divided by
Voltage = 220V
= 18.18A
So you basically can rate the breaker for 20A
To answer the question above.. they see 36A running... yes this might be correct but there is something called "in rush current". This is a spike in voltage and amperage when first turned on. It's like your car... whey you first fire it up... the rpms are high... then it goes back to a normal idle.. :)