How to Choose the Right Size of a Tankless Water Heater?

How to Choose the Right Size of a Tankless Water Heater? 03 Feb

Tankless water heaters are commonly referred to water heaters without the tank. Fundamentally speaking, a tankless water heater is a sophisticated home appliance that supplies warm water to a household. How big of a tankless water heater do I need? Well, tankless water heaters are known for several positive features, including the instantaneous and boundless water flow, low electricity intake, relatively simple installation process, low cost of maintenance, great durability, and longer warranty compared to tank water heaters.

What is a Tankless Water Heater?

Tankless water heaters are growing progressively popular in recent years compared to tank water heaters. Even though tankless water heaters and tank water heaters perform the same task, they have several distinctive differences. Tank water heaters are designed to hold a specific volume of water. The prices of tank water heaters vary depending on the number of gallons a particular tank water heater can have. Once the stored hot water runs out, a tank water heater takes some time to heat the incoming water.

On the other hand, tankless water heaters do not store water. Instead, tankless water heaters continuously heat that is going through the heater. When using a tankless water heater, anybody can expect to get a steady supply of hot water as long water is supplied to their house. Another difference between tank water heaters and tankless water heaters is their energy efficiency. Tank water heaters tend to heat water progressively even when hot water is not needed. Thus, it uses lots of energy and burns money in the process. Unlike tank water heaters, tankless water heaters stop running when hot water is not needed.

Differences between Tankless and Tank Water Heaters

Generally speaking, tankless water heaters are providing a better experience than tank water heaters. Nonetheless, most people prefer tank water heaters over tankless water heaters because tank water heaters are cheaper at the time of purchase. However, in the long run, tankless water heaters are less expensive because of their long-term energy savings. Therefore, we urge you to opt for a tankless water heater. In the long run, they will recoup the cost of the initial investment. After that, you enjoy long-term energy savings.

Factors to Consider

There are different sizes of tankless water heaters. Generally speaking, households need different sizes of tankless waters depending on the house’s size, the rate of water flow in a particular residential or commercial area, the temperature preferences, and the number of people in a specific household.

So how to choose the right size of tankless water heater? You have to always remember that tankless water heaters are categorized according to their maximum temperature rise possible at a given flow rate. Therefore, the ability to choose the right size of a tankless water heater depends on the flow rate and the temperature needed for the tankless water heater’s useful application within a household. It is also essential to understand that it’s not a good idea to buy a small tankless water heater to save money.

Factor 1

Every person wants to have a supply of hot water to the entire house, the first factor that needs to be considered is the size of the house. Failure to check it may lead to a situation where you have hot water that flows into the rooms rather than the entire house. Proper consideration of the house’s size is necessary for determining the overall volume of hot water required for the whole house.

Factor 2

How big of a tankless water heater do I need? The second factor that must be considered to choose the right size of a tankless water heater is the maximum number of appliances that will use water from the water heater. Every appliance has its different flow rate, and the overall flow rate of a particular house is essential in determining the right size of a tankless water heater. The general flow rate got by adding the flow rates of each appliance expected to use hot water.

Factor 3

The third and most important factor is the overall flow rate required at any given time. The general flow rate is the sum of each appliance’s flow rate expected to use hot water from the tankless water heater. In simple terms, if you want to concurrently run a particular hot water valve that has a flow rate of 1 gallon per minute and a shower head with a flow rate of 2 gallons per minute, the flow rate will have to be at least 3 gallons per minute. The third factor in choosing the right size of a tankless water heater is the temperature rise. How can you calculate the temperature rise? To determine the prerequisite temperature rise, you should deduct the water temperature that goes into the tankless water heater from the output temperature you need.

Factor 4

The fourth factor that must be considered is the climate of the area where you intend to install the tankless water heater. If the tankless water heater is installed in a cold environment, a tankless water heater with a higher temperature rise is the best choice. It is important to note that you must always choose the lowest possible temperature to avoid under-sizing a tankless water heater.

Factor 5

The fifth factor that needs to be considered is the size of the household. Logically, people do not use hot water at all times, but every household experiences skyrocketing hot water usage at certain times. In most cases, hot water usages tend to hit the roof when there are several simultaneous activities from different people. Hence, there is a need to consider the size of the household. The size of a home allows an individual to estimate the highest possible usage of hot water at any particular point in time. The highest possible use of hot water is essential in determining the size of a tankless water heater.

Factor 6

The power source for your tankless water heater is the next consideration. There is no easy answer to which source of power is best for your tankless heater. The electric power supply is best suited for smaller households. First, determine the power source in your house and then evaluate the size of the tankless heater you require.


Generally, tankless water heaters are highly efficient. Logically, there is no need to pre-heat the water that enters a tankless water heater. It is also important to note that most tankless water heaters are rated for a wide array of inflow temperatures.

Call Smile HVAC

Smile HVAC is a reputable Canadian-based company that specializes in all HVAC related services. Smile HVAC’s highly trained personnel are best equipped to provide a tankless water heater sizing guide needed to efficiently serve the needs of any particular household or commercial premise. Furthermore, Smile HVAC provides other additional services related to tankless water heaters, such as installation.