1350watts will heat water for mashing/sparging, but it will take quite some time. It will not be enough to boil however. For refernce, my 1650watt element in my HLT takes about 2-2.5 hours to heat 8 gallons of HLT water + 5-6gallons of strike water from 55 to 155 recirculated through the herms coil. The 1650watt element in the boil kettle will heat to a boil, but you have to keep the lid on and cracked. Hasnt caused any DMS issues and i've made some fantastic beer with my system
2250 watts will get you there faster, and boil a bit easier with the lid further off, but you're almost maxing out a 20amp circuit, if not fully maxing it out. I brew on a 20amp outlet but with my element and 2 pumps combined i'm only running around 16ish amps so i have plenty of room. Electrical code typically requires you to put no more than 80% load on a circuit, so on a 20amp circuit you really shouldnt be running more than 16-17amps safely.