Get Fast Hot Water and Be Green
While it is true that tankless electric water heaters save energy and can provide an endless supply of hot water, it is also true that tankless units take longer to get hot water for luminaires. Since a tankless water heater needs to heat the water before it can provide hot water for you, you have to wait longer. The only way to get hot water is safe to open the valve. So while you run the faucet and wait, you are dumping gallon after gallon of pure drinking water to the sewer. The water to energy for pumping and treatment. Pumping and treating water uses energy which in turn means greenhouse gases released into the atmosphere.
The heater can be described as a long piece of pipe wrapped and placed on a fire. As water flows through the tube, it becomes warmer. To reach the full temperature, it must remain in the fire for a certain period of time. It will take longer if the water starts to cool. If you speed the flow of water, it will be cooler, unless you add more fire. With the old storage heaters tank filled with hot water is ready to go when the valve is open so you get your hot water faster.
With tank type heater to what has been done in the past both to accelerate the delivery of hot water and remove the water running in the sink while you wait is to create a loop in the warm side of the plumbing to allow you to pump hot water around the loop, keeping the pipe full of hot water. That way, when you open the tap, you get instant hot water every time when you want. It works very well with a tank type heater except that it uses a lot of energy keeping the pipes warm.
But you can not do this with the unit tankless water heater tankless because light up when they detect water flowing through them. Usually it takes ½ gallon per minute flow rate or more to activate most tankless water heaters. Most systems do not produce much traffic that result. If they were available, the heater is at any time. Using a standard system of movement with a tankless water heater will void the warranty in most cases, anyway.
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Can I use a tankless water heater and a reservoir style one at the same time?