Tankless water heaters are rated based on the maximum temperature they can provide and also the power of their flow rate. Hence to determine which heater is the more efficient one, it is important to look into both this parameters.

One should also take note of the size of the container. After all it can impact the temperature of the water. The bigger the container is, the more power is needed.  So, before making a buying decision of which tankless heater to get, make sure to opt for the right size by considering the factors mentioned below.


1.Maximum number of devices you wish to run

Look at the maximum number of devices you want to run and their flow rate. For each device a different flow rate should be specified, and at the end everything should be added up. At the end, you will arrive at the desired flow rate which you should for in your heater. So, if you wish to run faucet at 0.75 gallons per minute and also shower and 2.5 gallons per minute, then the minimum flow rate a heater should have is 3.25 gallons per minute.

  1. Rise in temperature

The required temperature rise should be calculated. The appropriate way of calculating required temperature is by subtracting the incoming temperature from that of the output temperature. For individuals who are living in cold places, they would like to have significant rise in temperature especially in comparison to people who are living in warmer places.

  1. Size of the tankless water heater

An average shower is about 104° and makes use of 2.6 gallons of water.  Hence for users who on an average wishes to use the shower twice in a day, they would need a heater that can efficiently heat approx.. 5.2 gallons in a day. Purchasing anything which is less than the specified gallon amount, will not be able to meet the user needs leaving him unsatisfied. It is thus important, to study on the factors affecting size in advance and thereby take a learned decision.

  1. Flow rate

Flow rate is one of the most important factors, and to inquire on this you need to find out how much water you need in one go. For individuals who wish to use the faucet, shower and other water outlets in one go consuming 5 gallons of water, it is important you choose a tankless gas water heater which has minimum flow rate to satisfy user need. The flow rate should be able to produce 5 gallons of water in a minute thus satisfying need of a user, and thus fulfilling his needs of having a hot water at his disposal.

  1. Other sizing factors

The gas tankless water heaters are capable of producing large temperature rises, especially when compared to the electric models. It is not always advisable to have a heater that has faster flow rate or cooler inlet, as this can have adverse effects on the heater causing the temperature of water to lower down much faster.


Contributed by: Perfectbath.com  Foremost experts in bathroom design and function.