It depends which brand & model you are looking at. The smaller units don't work so well in colder climates. So be careful which model you choose. Most tankless heaters work well, but colder inlet water calls for more btu's. The bottom line is, the more hot water you need, the bigger the unit you need. If you need more info, please e-mail me, or call me 800 851 9891. I hope I helped some. Regards, Brian.