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What Size Tankless Water Heater do I need?

A household needs a powerful water heater if the water is freezing, and it is much needed if you are residing in a cold environment and cold climate countries that’s why switching to a tankless water heater is the best decision you’ve made to provide you your hot water needs.

Before we provide you a simple guide on what size a tankless water heater best suits you, here is an overview of what a tankless water heater is and why using it is way better compared to the conventional storage water heater.

In tankless water heaters, you can heat water directly without using a storage tank. They provide hot water only as it is needed. They are more energy efficient as compared to regular storage tank water heaters. Also, these tankless water heaters may initially cost high but in the long run it will offset its high value because they are low-maintenance and their life expectancy is longer than the conventional storage water heaters.

Your household hot water needs are more efficient if you have an appropriately sized tankless water heater. That is why it is important to ensure its correct size before purchasing.

The following are important considerations that influence the size of a tankless water heater you need in terms of flow rate. Flow rate is the amount of fluid that flows in a given time, measured in gallons per minute (GPM).

Incoming Water Temperature

To size a tankless water heater, it is important to determine the temperature of incoming water in your area. Apparently, the colder the water in the area the more significant the water heater is needed.

You have to determine the temperature rise you need. (Temperature rise can be identified by subtracting the incoming water temperature from the desired output). If you live in a cold country, your incoming water temperature will be much lower; therefore you will need a much bigger tankless water heater to reach that higher temperature rise. For example; the incoming water temperature in your area is 55O F and you want your water temperature at1000F. In this example, you will need a tankless water heater that can produce a temperature rise of 450F. The temperature rise varies depending on the temperature of the water that you need.

Accommodation Size

The area of your home and the number of people living on it constitutes a big factor of higher hot water consumption or demand. A bigger area requires a bigger size of water heater, in other cases; some household requires multiple tankless water heaters instead.

Below is an approximation table containing the consumption of hot water depending on the accommodation size of a household.

AccommodationBathroomsGPM
Apartment/Condominium13.0 GPM
Small House (<1000 sq. ft.)14.0 GPM
Average House (<1600 sq. ft)27.5 GPM
Large house3+10+ GPM

Peak Demand

In a regular household, hot water can be used in multiple activities and household chores. We use hot water not only during bathroom shower but also in washing clothes, using the dishwasher and kitchen faucet to name some. For better understanding, the table below will show the demand type and the average amount of water consumed.

ActivityDemand Size
Standard shower2.5 GPM
Bathroom Sink0.5 GPM
Dishwasher1.0 GPM
Low-flow shower1.5 GPM
Washing Machine1.5 GPM
Kitchen Sink0.5 GPM
Laundry Sink1.0 GPM

More significant demand for hot water does not necessarily lead to a bigger size of tankless water heater. We can efficiently manage our household activities to lessen the peak demand and save on the size that you need. One can always come up with a strategy for load shifting which will result in a peak reduction. Make a schedule of household activities to limit the simultaneous use of multiple water sources.

Power Source

“Which tankless water heater will I choose? The gas operated or the electric one?” This is one of the usual questions asked by some homeowners before purchasing.  The choice for your power or fuel source depends on some factors. In the United States, most homes have the availability of natural gas, so it is easy to choose a gas powered tankless water heater. Some communities don’t have the access to natural gas that is why they have to buy the electrically powered heaters. Tankless water heaters that are gas-powered tend to have higher flow rates compared to electric powered; therefore you have to purchase multiple units when using electricity.

Water Hardness

Did you know that the lifespan of your tankless water heater can be affected by the type of water that is available in your household? Although not related to size factor, this is where the water hardness factor will show its importance on why you should reconsider switching to a tankless water heater.

Water hardness is measured by its mineral content, mainly by magnesium and calcium. The mineral content varies on the region where the water is collected, treated then distributed to your home. Eventually, these lime scale will block the water pipes and build up in your water heaters and will cause you higher utility costs and maintenance. The scale buildup will bring the heat exchanger to overheat.

Soft water contains chloride, nitrates, and sulfates which will have a negative impact on your water pipes.

While balanced water is the best water type to give protection against pipe corrosion and build up. Low mineral content is good for your health.

You can treat your hard water with a water softener. This is the best way to help your tankless water cleaner and sustain the excellent quality of your plumbing system. An infrared electric water heater is also available in the market as an additional option.

How to Size a Tankless Water Heater

  • Incoming Water Temperature
  • Peak Demand
  • Accommodation Size
  • Power Source
  • Water Hardness

With all the considerations given to you, and after identifying the primary factors needed before purchasing, we hope that you can finally decide for the perfect size of tankless water heater suitable for your hot water household needs.

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