I calculated heatsink for 500W(2.27A) load to be max 20 K/W (Tj max = 125C Ta=50)
Power dissipation of the triac is max 3W (@ 2.27A RMS and 180°).
So a 20K/W (junction to ambient) heatsink causes a 60K temperature rise. If the max junction temp is 125°C then the max ambient temp is about 65°C.