Every home needs hot water, but how you heat that water can be very different from your neighbor. Some people like to keep it simple with a standard atmospheric vent hot water tank.
This is exhausted out a chimney, and usually comes with in 40 or 50 gallon tanks. Maybe you’ve upgraded or you’re in a newer home with a power vented tank.
This is very similar, but it has a fan to blow exhaust outside to add efficiency. Some of you may even have the most efficient water heaters.