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How To Choose The Right Size Tankless Water Heater

Couple washing dishes

With the approaching cold weather, we all love the ability to turn on the tap and feel hot water. In fact, hot water is an incredibly important part of our daily routines, allowing us to clean our bodies, homes, clothes, and so much more. Therefore, choosing an appropriately sized water heater to address your household’s needs becomes very important.

Many homeowners remain loyal to conventional hot water heaters, but others are turning to the newer tankless water heating options. If you are still trying to decide, check out our recent post, Tankless Water Heaters: Understanding the Pros and Cons. If you’ve already decided on a tankless water heater, here are some tips for helping to choose the right size. It is important to note that you should never try and save money by undersizing your tankless water heater.

Understanding the Water Heater’s Capacity

Unlike conventional tank-system hot water heaters that use a first-hour rating, tankless water heaters, also known as demand water heaters, are rated by the maximum temperature rise possible at a given flow rate. Simply put, they are measured by how hot they can get for a specific output of water per minute.

Therefore, to size a demand water heater, you need to determine the flow rate (the amount of water required per minute) and the temperature rise (how hot the water needs to get from its untreated temperature) necessary for its application. Sometimes this application is for the whole house, and sometimes it is a remote application for a specific room, such as a bathroom.

Sizing a Tankless Water Heater

Step One – Determine the Desired Flow Rate.

First, you must ask yourself how many hot water devices will be operating at the same time in your home at a peak time. For example, is it common to have two people showering, while the breakfast dishes are being washed in the morning? Or, do you live alone and generally only use one hot water device at a time?

Use the chart below to add up the “average flow rates” of each device you normally operate simultaneously during your peak water usage time of the day.

Step Two – Determine the Required Temperature Rise.

To determine the temperature rise, subtract the incoming water temperature from the desired output temperature (use the chart below as a general guide). Unless you know otherwise, you can assume that the incoming water temperature is approximately 50ºF (10ºC). For example, if you would like to take a shower at 104ºF, you would subtract 50 from 104 to get a required temperature rise of 54ºF.

desired output temperature for water heater

Call In The Experts

Choosing the hot water option that fits best with your family’s needs can be complicated, but your Just Right Services technicians can guide you through the process and ensure that your new system is installed safely and efficiently. Contact Just Right Services today at (949) 245-6320 to get trusted advice about your hot water heating system.

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