If you have ever hopped in the shower and turned the water on only to realize there is no hot water left, you know how frustrating running out of hot water can be.  Not only are tankless water heaters more energy efficient than traditional tank water heaters, they will ensure you always have the hot water you need when you need it.  Energy.Gov explains how tankless water heaters work, “Tankless water heaters heat water directly without the use of a storage tank. When a hot water tap is turned on, cold water travels through a pipe into the unit. Either a gas burner or an electric element heats the water. As a result, tankless water heaters deliver a constant supply of hot water. You don’t need to wait for a storage tank to fill up with enough hot water. However, a tankless water heater’s output limits the flow rate.”

You ‘always’ have hot water with tankless water heaters because they heat water on demand. But, while they heat water on demand, they can only take so much demand at a given time which can be problematic for larger households.  If you have a larger household you tankless water heater may not be able to heat water on demand as quickly as necessary and if that is the case, larger households will do well to invest in two tankless water heaters.  This will ensure that there is more than enough hot water to go around while still reducing energy waste that traditional water heaters would typically produce.  Energy.Gov further explains why some households opt to install two tankless water heaters so that they never run out of hot water, “Typically, tankless water heaters provide hot water at a rate of 2–5 gallons (7.6–15.2 liters) per minute. Gas-fired tankless water heaters produce higher flow rates than electric ones. Sometimes, however, even the largest, gas-fired model cannot supply enough hot water for simultaneous, multiple uses in large households. For example, taking a shower and running the dishwasher at the same time can stretch a tankless water heater to its limit. To overcome this problem, you can install two or more tankless water heaters, connected in parallel for simultaneous demands of hot water. You can also install separate tankless water heaters for appliances — such as a clothes washer or dishwater — that use a lot of hot water in your home.”