Electric element power

[PalCabral]

Hiya,

another noob question. I have two 2500w electric elements in my boiler. When I run them via the regulator on 50% each, I have been assuming the power I am putting into the heating of the boiler is 1250w + 1250w = 2500w, but that's not what I am getting out. Reverse calculating I am more like getting 1600-1800w in total when running on (what I think is) 50% each. Either I am really not running of 50% like I think I am, or 1+1 <> 2 when it comes to counting watts? I am clearly missing something. Yes, I am not the sharpest tool in the box.