We have an old HP C7000 at work. It pulls 423W empty, 560W with a single blade. Safe to say it’s a bad idea.

But regarding your question: You already have the thing, so measure it for actual use, as your workloads will most likely vary over time. Or to calculate: E(kWh) = P(W) × t(hr) / 1000, so 3833.025(kWh) = 5250(W)x730.1 The number of hours per month is an average over a year.