Your water heater is one of the largest consumers of energy and thus money in your home. This makes it a prime target for finding was to be more efficient, greener, and to reduce your carbon footprints.
The differences between storage water heaters and tankless water heaters are not trivial, and should be carefully considered before making your choice of which would work better for your needs.
Most people in the United States have grown up with a standard tank type water heater, and are at least able to identify as that round tank out in the garage. Tankless water heaters have been in use in many parts of the world for many years, they are not a new technology, just new to most of us in the U.S.
Tank type water heaters can be easily pictured as a big tank of hot water either sitting over a gas burner, or with heating elements inside the tank in the case of electric water heaters. The tankless water heater can be pictured as a few coils of copper pipe either sitting in the flames of a burner, or with some form of electric resistance heating being used, like maybe wrapping the heating elements around the coiled pipe.
Water Heater Operation – Storage Type
Operation of the tank water heater is very straight forward. The tank has a thermostat inside, and when the water in the tank drops below a preset temperature the thermostat comes on turning on the gas burner or the electric resistance heating elements. When the temperature reaches its upper limit the thermostat tells the burners or heating elements to turn off.
It doesn’t matter what the temperature of the incoming cold water is, the burners just stay on until the set point temperature is reached. The colder the water of course, the longer it takes to heat whole tank of water. You will get the same temperature of water out of your heater no matter what the incoming cold water temperature is.
Tankless Water Heater Operation
With a tankless water heater you have to have some water flowing while the burners are on. If the water for some reason stopped flowing and the burners stayed on (or the heating elements with electric tankless water heaters), the amount of heat could not be carried away by the water so it would quickly overheat the tubing and or cause the water to turn to steam and risk an explosion etc.
That is why tankess water heaters need a flow switch and won’t turn on unless enough water flows through the unit, typically 1/2″ gallon per minute to 3/4 gallons per minute.
The fact that the heater needs a minimum flow of water to stay turned on can force some behavior changes on the user. For instance, if you want a low-flow of warm water you might not be able to achieve it. Since to get a warm temperature from the fixture you need to mix cold water with the hot water to get the temperature you want. If you have a tankless heater that requires 3/4 gallons per minute and you have to mix more cold water with it to cool it down, you may end up needing to run over 1 gallon a minute. No more getting just a trickle of warm or hot water.
If you have very cold incoming hot water or a high flow rate you can exceed the capacity of the tankless heater to provide sufficient temperature rise and your hot water will have a reduced temperature.
With the tankless water heaters you need to stay within a range of flow for a stable outlet temperature. Tank type heaters don’t have any of these problems.
If you’re considering a tankless water heater because you frequently run out of hot water with your storage heater then you can’t beat the tankless unit. They are more efficient in that they do not have a tank of water losing heat 24 hours a day so it may save you enough money to pay for itself.
Replacing your existing storage water heater may require a larger flue, venting and a large gas line if it is a gas heater, and much heavier wiring and a separate circuit and breakers if it is an electric water heater.
When choosing a tankless water heater sizing the heater is the most important thing you need to consider. Too small and your hot water will not have a stable temperature, and if the heater is too big you will have trouble getting low flows of moderate temperature water.
More about storage water heaters. Storage Water Heaters
More about tankless water heaters. Tankless Water Heaters