If your house is set up for it, they do work. Keep in mind, though, that you probably will need to expand your gas supply line and have provisions to provide combustion air. The things are rated at degree rise at certain volumes. The more water you request, the colder it will be since you can only transfer so much heat in the time the water passes the coils. To meet the requirements of say two showers running at the same time, you might need two of them in series (not all of them can do this). Maintenance can be expensive and parts are not stocked everywhere. A gas tank type or electric can be serviced with parts from almost anywhere.