Well, I decided I was going to go with all copper plumbing, and the closest to a 2000W heater I could find with a low watt density was a 1700W LWD heater. So using that, 1700/120=14.2A. Add in the pump, and I'm right at 16A. I think I should be safe where I'm at, but if I decide to upgrade in the future, this will be something I'll address then. I will make sure that outlet is rated for 20 A. Great point about the outlet though! It's a cased outdoor porch outlet, so I feel like it's one that they wouldn't be able to cheap out on as easily, but you do never know.