Tankless Hot Water Heaters

 Tankless hot water heaters heat water directly without the use of a storage tank. They avoid using energy to keep a tank of water hot regardless of whether or not it is needed. With a hot water tank the temperature of the water is maintained 24 hours a day. It’s kept warm over night when you’re sleeping and when you’re not home. Tankless water heaters need to quickly heat a smaller amount of water so that when you turn on a faucet, you don’t have to wait long before the hot water comes out.

When a hot water faucet is turned on, cold water travels through a from the homes cold water supply into the tankless hot water heater. Either a gas burner or an electric element heats the water via a heat exchanger. As the water flows through the piping of the heat exchanger its temperature rises. When operating, tankless hot water heaters provide a constant supply of hot water.  The volume of hot water supplied by tankless hot water heaters, their flow rate, that can be created is limited by hot quickly the water can be heated.  

Tankless Hot Water Heater Diagram

Tankless hot water heaters provide hot water at a rate of 2–5 gallons (7.6–15.2 liters) per minute. Gas-fired tankless hot water heaters produce higher flow rates than electric ones. The reason that the flow rate is important is that even the largest, gas-fired model cannot supply enough hot water for simultaneous, multiple uses in a large household. For example, taking a shower and running the dishwasher at the same time can stretch a demand water heater to its limit. To overcome this problem, you can install multiple tankless hot water heaters, connected in parallel. You can also install separate tankless hot water heaters for appliances—such as a clothes washer or dishwater—that use a lot of hot water.

For homes that use 40 gallons or less of hot water daily, demand water heaters can be 24%–34% more energy efficient than conventional storage tank water heaters. They can be 8%–14% more energy efficient for homes that use a lot of hot water—around 80 gallons per day.

The key considerations when replacing your hot water tank with a tankless system are as follows: 

Is the gas supply and venting available to use for the tankless unit?  If you have an existing gas or propane hot water heater then the gas supply and venting will be available to utilize for the tankless unit. If you currently have an electric hot water heater then you will need have gas piping installed to the unit and you will need to know that you can properly vent the exhaust gas to the outdoors. It is best, unless you really know what you are doing, to hire a professional to install the gas line and venting to be sure that there are no leaks in the supply line and that there are no gases getting back into your home from the exhaust. If you are converting from a electric hot water heater with a tank to a tankless hot water heater also consider a heat pump hot water heater. Both tankless and heat pump hot water heaters are more expensive than a traditional tank water heater but the heat pump hot water heater won’t require any changes when converting from an electric tank system as they are similar in how they install.

Will a single tankless hot water heater allow you to meet your homes peak demand or will you need more than one installed in parallel?This will have an obvious impact on your upfront cost.

Are there government or utility incentives that you can take advantage of to reduce your upfront costs?


The following is a photo of a Rinnai Tankless Hot Warer Heater:


Rinnai Tankless Hot Water Heater

Also see:

Tankless Hot Water and Inside Look

Types of Hot Water Heaters.