According to the NEC you size your over-current protection and wire/outlet for 125% of your continuous load. On a 20A circuit you can safely run 16A by the book. With a 1000W/120V load you are drawing approximately 8.3...A (not including power factors and efficiency). You're well within spec for your circuit.
The problem you might run in to is that there can be up to 7 outlets on a circuit (derating factors and whatnot). Though most houses you only see something around 4. Any load you add to those outlets will add to your 16A mark. Also while your circuit breaker may be rated for 20A the outlet might only be good for 15A (though this is really unlikely in any modern home).
Why is 15A unlikely in modern homes, what's the new standard where you live?
In Europe we use 16 amp breakers for wall sockets ("schuko"), except for the stove, thats 3x16A if I'm not mistaken. The wiring is also rated for no more than 16 amps on the sockets (with some overhead of course), so if I were to put 20A on the "wall socket group" breaker it could potentially screw up the wiring in the long-term.
Well from what I've seen around where I live in the midwest. Most contractors are using 20A outlets and 12/2 NMC simply because they dont have to carry 15A stuff and 14/2 (unless using it for lighting circuits) on their trucks. More material means less trips to the Home Despot. Its not a written standard, Its just something I see most contractors doing. Here its pretty commonplace to "over build" the branch circuits a little since the fire marshal can interpret the code as he sees fit during rough-in inspection. Outside of the midwest I'm not sure if its the same way. I could be wrong to assume the rest of the US is doing this.
In the EU you guys are obviously running that premium octane voltage so 16A is more than enough to power most stuff at the same wattage.
Since no one else commented on this, I thought I'd set the record straight, so no one tries to do this. If the UPS tries to pull, say 1900w, from a 15A circuit, it will trip the breaker on the circuit. A UPS is designed to continue to supply power when the socket fails to deliver. It will not supply more power than a circuit can provide. In fact, you'll be hard pressed to find a UPS that has a NEMA 5-15p socket and can provide more than 15a of 120v power.
Oh yeah, the voltage difference, I forgot about that.
Well, if you put thicker wires in walls to avoid fires or feel safer (or for longevity), than don't beef up the fuses. If you oversize them to get more kick, then by all means enjoy moar powuh,
I didn't reply to that guy directly but I did mention it in my post (#14) above. I did forget to mention that UPS can continue to supply power when it goes out.
