I installed a 50 gallon Bradford White Defender tank with a power vent in my home and it works extremely well. The power vent is nice in that it exhausts directly through a pvc pipe that comes out the side of the house - just like the high efficiency furnaces. No pilot light to worry about and it is 40,000 BTU.Just a natural gas standard residential water heater 40 gallon 40,000 BTU's will likely work. Just look at the first our ratings on the water heater keeping in mind if it doesn't keep up when you're super busy you're still going to have hot water It just won't be quite as hot.