A 2kW dimmer shouldn't be that expensive and he's not building a dimmer which uses phase control, he's decided to opt for PWM which will be cheaper because it doesn't require large RFI suppression inductors and is easier on the TRIAC.
I Googled for a suitable TRIAC, found the MAC15A6G and its datasheet.
http://pdf1.alldatasheet.net/datasheet-pdf/view/172093/ONSEMI/MAC15A6G.htmlIf the current is 10A and its conducting both for the full cycle, the power dissipation is about 11.5W (see graph on datasheet).
The thermal resistance from junction to case is is 2
oC and the maximum junction temperature is 125
oC.
If the ambient temperature is 40
oC the maximum allowable thermal resistance between the junction and ambient is (125-40)/11.5 = 7.4
oC/W
Assuming an extra 2
oC/W for the thermal pad and a safety margin, a 3
oC/W heatsink will be fine and is not very expensive.
Also note my point about PWM being easier on the TRIAC and dissipating less power than phase control: compare the dissipation at half the power setting, with PWM at 50% duty the power dissipation is 5.75W, with phase control and a 90
o firing angle, the power dissipation is about 9.25W. This is because when the TRIAC is triggered at 90
o lots of energy is dissipated to the power dissipation is higher even though the RMS current is the same as with PWM when the duty cycle is 50%. Using PWM, there are no switching losses, only conduction losses.