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How to Choose the Right Tankless Water Heater

How to Choose the Right Tankless Water Heater

Deciding to get a tankless water heater is easy. They are eco-friendly, cost efficient and provide an endless supply of hot water!

However, choosing the right one is where it gets tricky. There are a variety of factors you need to consider in making sure the one you get fits the requirements of your home. After all, you don’t want an overpowered model, nor do you want one that gives you a cold surprise midway through a shower.

Let’s take a closer look.

Make sure you get the correct size

Firstly, you need to ensure you correctly size your tankless water heater. What does this mean? 

Basically, you need to figure out the hot water requirements of your home. For example, let’s say you intend on running a washing machine, dishwasher and shower at the same time. 

The average flow rate of each of these appliances is 4.0 GPM, 2.0 GPM and 3.0 GPM. GPM stands for gallons per minute. If we total this up, that means we need a tankless water heater that can at least provide a total of 9 GPM of hot water.

Ok, so you’ve determined the flow rate. Now you need to know the temperature rise. This refers to a water heaters ability to increase the water temperature of the incoming water. 

If you live in the U.S.A the average incoming water temperature can range from 40°F – 80°F. 

As an example, let’s say the incoming temperature of where you live is 50°F. And say you want to use your tankless water heater for the shower which has an average temperature of 105°F. That means you’ll need a model that can accommodate a temperature rise of at least 55°F.

When we put this information together, we need a tankless water heater that can support at least 9 GPM with a temperature rise of 55°F.

Power Source – Electric or Gas?

When it comes to tankless water heaters, there are two main types – gas or electric.

With an electric model, you need to figure out the electrical output of your home and if it can support a tankless water heater. It is best to consult an electrician before moving forward with an installation.

Although electric models are generally cheaper upfront, the power consumption can be quite high. If you find that you need to upgrade your homes electrical system to accommodate a new tankless water heater, the cost of installation will significantly jump.

Gas is a more powerful solution than electric but costs more to install. However, it is generally a lot cheaper. Something like 30% more affordable than electricity.

With gas as the fuel source, you will need proper venting that will need to go through a roof or wall. However, with an outdoor model, venting isn’t required.

It is also possible to get a model with a condensing unit which does not require venting as it uses the heater from the exhaust. Although more expensive upfront, such a unit has a higher efficiency rating and so will be cheaper to operate overtime.

Again, it is best to call your gas provider and even have a technician come over to confirm your gas supply capabilities.

Single or Whole House?

You can use tankless water heaters as a whole house solution or for single point applications (for example, just for a shower head).

For whole house usage, a gas model is probably your best bet whereas a much more affordable (but weaker) electric model is perfect for one room or outlet.

There are also other things you need to consider. 

If the property is a new construction, it is a lot easier to run the appropriate cables and gas lines to the right point of use applications, so several tankless water heaters are easily doable.

If the house is already constructed, a whole house tankless water heater is the way to go since you can connect it directly to the main supply and avoid additional wiring or piping.

You may think that a whole house tankless water heater would be a lot more affordable, but this isn’t always the case.

Single point applications that are closer to the output are more efficient since the water will travel a shorter distance. They are also a lot cheaper individually. If you were to get electric models, maintenance and efficiency is even higher.

Whilst the upfront cost of several smaller tankless water heaters will be greater than a larger powerful one, the running costs may prove to be cheaper.

Outdoor or Indoor?

If you live in a warmer climate, an outdoor installation may be the way to go. This is because the warmer weather will not strain the heating capabilities of the tankless water heater. In a colder climate, an anti-freeze system will need to be used which can use a lot of energy.

As mentioned earlier, if you are using a gas model, outdoor installation is also a great idea as you won’t have to install any vents.

When it comes to indoor models, you need to choose where exactly in the house to place it. Tankless water heaters are quite compact, so it shouldn’t be much of a struggle to place it inside a cabinet, under the sink or other hidden places. 

To cut down installation costs, it is a good idea to install it closer to the existing hot water, gas or electric lines. 

Whilst indoor models won’t suffer from the elements, they can be in contradiction to your home décor. Some models are also quite loud when being used, especially when under strain.


Of course, tankless water heaters come with a variety of features depending on which model you purchase.

For example, some will automatically regulate the flow of water in the case where your house exceeds the maximum GPM supplied. In this case, the flow of water will be reduced so as to keep the hot water running.

Other’s will have a digital temperature output that you can set whilst some will simply have a dial that will allow a ballpark setting.


Getting a model from a respectable brand is a good start in choosing your tankless water heaters. There are several top brands which you should look out for – Stieble Eltron, Rheem, Bosch, Takagi, Rinnai, Titan and EcoSmart. In fact, if you look at many reviews across the web, these tankless water heaters will consistently show up as some of the best you can get.

These brands are known for providing top quality service and support as well as quality models that will be durable and perform to the expectations that have been advertised. 


Warranty will of course vary from brand to brand. Some manufacturers will cover the entire model whilst others will only apply a different warranty to different components (i.e. the heat exchanger). There may also be a warranty for servicing which will ensure free support for a set amount of time.