Tankless Water Heaters 101

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Did you know that as much as 35% of your household’s annual energy expenditures go towards the heating of the water? If your home uses the average storage-type tank to provide you and your family with hot water, you probably spend between $300 and $800 per year heating hot water. With a tankless water heater, however, you could reduce the cost of water heating in your home by anywhere from $10 to $30 per month.

Traditional tank-style water heaters hold water in an insulated storage tank where water is heated to 120F and 140F. Even if you are not using hot water, a tank type storage water heater operates 24/7 to keep the water hot. Storage tank water heaters all suffer the same problem – energy is used constantly even though an average family only uses hot water on average 45 minutes per day. The rest of the day the stored hot water is radiating heat into its surrounding environment and thus cooling down. With gas-fired storage water heaters this effect is exaggerated because the heating flue that is used to vent combustion gases also acts as an effective heat sink to remove heat from the stored hot water. As much as 40% to 60% of your annual water heating budget is lost via this loss commonly called “standby losses” as the tank tries to keep the water from cooling when not in use.

Standby losses can become a thing of the past, however, when you decide to install a tankless water heater in your home. Tankless water heaters, which have long been popular in both Europe and Japan, heat water by moving cool water directly over a heating element and warming it to a desired temperature. There are no standby losses with tankless water heaters because there is no water stored hot. With tankless water heaters – all the heat is produced on an “as needed” basis so when no hot water is needed – no energy is used. This methodology of heating water only when needed saves you money every month in lower energy bills and has the net effect of reducing your home’s carbon footprint.

Although there are those that argue a tankless water heater uses “much more energy” than a typical heater the fact is this is not true. The reality is that all tankless water heaters uses substantially more energy when in use – but the periods of use are short and thus when compared with a standard storage water heater – the total energy usage is much less. Additionally, a tankless water heater offers the additional functionality of “endless” hot water – so if you have the occasional visitors for the weekend everyone can enjoy a hot shower without waiting!

If you are ready to purchase a tankless water heater for your home, there are typically two approaches: installing one whole-house unit to supply all of your hot water needs, or installing smaller point-of-use units at several points around your house to meet the demand for hot water in several places. The largest consideration in choosing how to meet your household’s hot water needs is how much hot water you use at once. The average water faucet can flow between .75 and 2.5 gallons of water per minute while a dishwasher uses one or two gallons per minute. If you ran both at the same time, then you would need a tankless water heater that could heat up to 4.5 gallons of hot water per minute. If in your house you typically run the dishwasher, one person takes a shower and someone puts a load of laundry in the washer at the same time, add up how many points in your house need hot water at peak demand, then select either one whole-house unit that can accommodate your hot water usage, or select several smaller units to install that will meet your hot water needs where installed. In this way, tankless water heaters can give you both the flexibility and savings that traditional tank-style water heaters cannot.

What does the future hold? With an increasing move to eco-friendly and sustainable households we can expect home builders to move away from centralized heated water towards decentralized heat – as is the case in the rest of the world. In my next article I will explore this concept further.

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