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Does a tankless water heater supply instant hot water to your tap?

A tankless water heater does not provide “instant” hot water in the sense that hot water comes out the moment you turn on the tap. Instead, it provides “on-demand” hot water. This means that the water is heated instantly as it passes through the unit, but there is still a delay between the moment the tap is turned on and when the heated water reaches the tap. The time it takes for the hot water to arrive depends on the distance between the water heater and the faucet.

How Tankless Water Heaters Work:

  • When a hot water tap is turned on, cold water travels through a pipe into the tankless water heater.
  • An electric element or gas burner heats the water as it passes through the unit.
  • Since the water heater starts heating water only on demand, it doesn’t supply hot water instantaneously. The delay you experience is due to the time it takes for the heated water to travel through the plumbing to reach your tap.

Factors Affecting Hot Water Delivery Times:

  1. Distance: The further the water has to travel from the heater to the tap, the longer it will take to receive hot water.
  2. Flow Rate: The flow rate of your plumbing fixtures can also impact delivery times. A higher flow rate means water moves faster through the pipes, reducing the wait time.
  3. Type of Plumbing: The type of pipes (e.g., copper vs. PEX) and their diameter can affect how quickly the water heats up and how long it retains heat as it travels.

Solutions for Instant Hot Water:

For those who want truly instant hot water, there are a couple of solutions that can be used in conjunction with a tankless water heater:

  1. Recirculation Systems: These systems circulate hot water through your plumbing so that hot water is always available near the points of use. Some tankless water heaters are equipped with built-in recirculation pumps, while external pumps can be added to others. This system can greatly reduce the wait time for hot water but may increase energy usage.
  2. Point-of-Use Tankless Water Heaters: Installing smaller, point-of-use tankless water heaters near specific fixtures (e.g., under a sink) can provide nearly instant hot water to that fixture by eliminating the distance the hot water must travel.


While tankless water heaters offer the convenience of on-demand hot water, eliminating wait times entirely usually requires additional solutions like recirculation systems or point-of-use heaters. Understanding the distinction between “on-demand” and “instant” hot water can help set realistic expectations for the performance of a tankless water heater in your home.

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