I'm a little curious as to why you want to relocate the heater. A hot water heater is typically located near to the fixtures that use hot water (kitchen, laundry, main bathroom). These fixtures a generally grouped together during building design to minimize the length of pipe runs to the fixtures, which cuts down on plumbing and allows hot water to reach the fixture quicker. If you move it 20 feet away from the fixtures, it will take a lot longer for hot water to reach the fixtures and you will run out of hot water sooner.