The i7-4790 is listed as 84 watt TDP
The i7-4790K is listed as 88 watt TDP
Quote from Intel:
Thermal Design Power (TDP) represents the average power, in watts, the processor dissipates when operating at Base Frequency with all cores active under an Intel-defined, high-complexity workload. Refer to Datasheet for thermal solution requirements.
More info -
https://en.wikipedia.org/wiki/Thermal_design_powerIn simpler terms, the i7-4790K is outputting (4) more watts of heat than the i7-4790 with stock settings (no overclock). The heat load on the CPU cooler is increased by (4) watts of heat.
An example of 4 watts of heat, would be like the heat produced from the old christmas tree light-bulbs. The ones that are the size of your thumb. They're also used in older night-lights. They're wattage consumption varies from 4 to 10 watts, depending on the bulb specs. So purchase one rated for 4 watts and put it in a night-light, and feel the heat it produces.
I don't think this should be a problem, unless you live in a hot climate
without air conditioning in the space the PC resides. Of course about any PC cooler is going to struggle at those temperatures/conditions. But overclocking the i7-4790K is definitely going to increase it's heat output, and may be a concern with G20 CPU cooler, as I'm not familiar with it's cooling performance.
With living in Canada, I expect summer weather is nice, but winter nights can be a bit chilly.
It's possible the latest BIOS patch is for the i7-4790K being introduced in the latest G20AJ, just a thought as I have no insider information.