At some point, the limiting factor is going to start being cooling in the room.
That's 900W for the GPU alone. The CPU can probably be north of another 200W, and then you will have other hardware you need to power.
I have a space heater that can do 400W on low, 800W on high.
Plus, power. A standard US household circuit is 15 (or 20, in some cases) amps, so even if you're dedicating an entire 15A household circuit to the PC, that's 1800W you can drive.