Why Does it Take So Long to Get Hot Water From Tankless Water Heater?
It is a pain to wait for hot water after having opened your tankless water heater. The delay may result in waste of water and energy as well. In fact, it is the distance between the water heater and the point of use that primarily determines the wait time to get hot water. For example, if your point of use is 50 feet away, and the water flow rate is 1 gallon per minute, then it will take 90 seconds for hot water to reach the point of use.
There are top brands as Rinnai, Titan, and Bosche etc than can produce hot water within a few seconds of first water flow from a cold start. However, the condition is that all the cold water needs to be purged out of the pipe between the tankless water heater and your point of use.
Let us examine the various ways to reduce the delay time for hot water reach your point of use. First, you should consider where you are going to install your water heater. Most of the modern tankless water heaters are of compact size. This will enable you to install the units in locations that you could never place a tank. If you can place a unit close to your primary points of use, such as, your kitchen or master bath you will have the best of all alternatives.
If this is not possible, there are three choices to reduce the wait time or waste of waiting for hot water:
1. You could use a re-circulating line that keeps hot water following through a loop in your water system and then through your tankless water heater. This is a poor choice for two reasons. First, it wastes a lot of energy (probably at least $100 / year). Second, it will reduce the life of your unit.
2. You could add a small electric hot water tank (only a few gallons) to the hot water side of your and run a re-circulating loop through it. The tankless water heater will still heat all the water and you will not shorten the life of your unit, but you will still waste energy. You could cut the energy waste by running the pump on a timer.
3. Another option is that you could add a cold water line re-circulating system to your common points of use. This system will circulate water from your tankless water heater to a point of use by utilizing your cold water line as a return. This will not only reduce the delay period for hot water, but also avoid water waste of water as well as extra energy consumption.