I have a server running 24/7 in my office, drawing 120 watts average (tested). Office is 10x10. It alone keeps that room 2-5 degrees warmer than the rest of the house. If I turn it off, room equalize to house.
As for comparison, those little square plug in space heaters consume 500 to 1500 watts, and you can see how much th heat.
1 watt = 3.4 btu
Depending on your use case, why not look to reduce power consumption? I’ve replaced that server with one that draws <20w at idle. That’s negligible.