A Size Guide to Determine What Size Tankless Water Heater to Replace a 50 Gallon

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Tankless water heating units are highly energy-efficient inventions. These units are only the size of a suitcase and can be mounted on a wall or placed on the floor. If you own a small apartment or have a house with multiple family members, such devices are highly recommended because they clear up room for other essential appliances in the home.

When replacing a 50 gallon water heater most buyers get confused about the question of what size tankless water heater to replace a 50 gallon traditional water heater.

The list of pros of a tankless water heater unit is not that small. These units reduce the energy bill by about 30 percent. This means more savings. More savings means you can save up money to buy more appliances of your need.

Tankless water heaters have a very simple operating technique. They work only when the faucet is turned on as this is on-demand water heating. This high-energy efficient unit will last for about 20 years with proper maintenance.

Selecting the Right Size of Tankless Water Heater

The right size of the tankless water heater depends on your family’s water needs. If you have a small family or you want a water heater for a single faucet then buy a small unit. If you have a big family of 3 to 4 or you want to use a single water heater for the whole house then purchasing a bigger unit will be best.

A unit that is smaller than needed results in lukewarm water. The unit is not capable enough to match the demand. The unit bigger than needed results in energy loss and so unnecessary bills. Thus it’s important to choose the right size water heating unit that will fulfill the hot demands of your whole family perfectly.

Factors Determining the Size of a Tankless Water Heater

Thinking of replacing your old water heating unit? It’s important to upgrade appliances of daily use. A water heating unit is used excessively throughout the year. Installing a unit that’s more efficient and budget-friendly is surely a great and important step. To access which water heater will work best for your family you need to look for two important factors.

  1. Maximum hot water needed for the whole house
  2. Gallon per minute capacity of the water heating unit

To calculate the hot water need of the whole house at all times it is important, to sum up, the GPM water requirement of all fixtures. Most faucets use between 1 to 2 gallons of water per minute. The water requirement of individual fixtures is listed next.

  • Shower 2.5 GPM – 3 GPM
  • Washing machine 5 GPM
  • Dishwasher 1.5 GPM
  • Kitchen Faucet 1 GPM
  • Bathroom faucet 1 GPM

This estimated water delivery of each faucet can vary from home to home. If you do more dishwashing than an average family cause all your meals are cooked at home then do consider this factor when making the calculation.

Tankless water heaters have a capacity of between 2 to 12 GPM. For smaller households, 8 GPM is enough. For bigger houses above 8 GPM water capacity will be needed.

Realistic Maximum GPM

The maximum GPM is mentioned on the front side of a water heating unit. The maximum GPM achieved in actuality is however different from the number mentioned. The reason for this discrepancy is that the GPM flow rate of a unit is calculated by assuming a 77 degree Fahrenheit increase in temperature. Thus your groundwater temperature matters a lot.

In warmer climates, the water temperature is already high so it takes less time and energy to raise it to the required level. In cold climate areas, there is more temperature difference between the groundwater temperature level and the required water temperature for daily use.

The inlet water temperature determines the water flow rate of the unit. Keep this important point in consideration while purchasing a tankless water heating unit for your home.

Right Size According to Your Family Size

One of the most asked questions is how much GPM tankless water heater unit is needed for a family? People want to know the exact numerical GPM value. If you have a family of 3 then a small unit will work fine for you. And if you have more than 5 members in your family then you need to install separate water heating units for separate faucets.

If you install a single unit for big family water will take a long to heat and the temperature will not be as required.

Temperature Rise

The average ground temperature varies from place to place. Temperature rise is the difference between hot water supplied by the unit and groundwater temperature. The higher the temperature rises longer it takes for water to heat up. For higher temperature rise there is a need for bigger units. The units with High GPM are better able to meet the expectations in cold climates.

Tankless water heaters are surely a need of the hour. Do you want to replace your old traditional water heater with a tankless one too? The old water heaters have a certain storage capacity.

Let’s imagine you have a 50-gallon water heater and now you want to replace it with a tankless water heating unit. A 50-gallon storage water heater has 50 gallons of heated water stored in a tank. In the case of a tank-less water heater, the water will be heated on demand.

If multiple faucets are turned on simultaneously or you do dishwashing and laundry at a time your stored hot water supply will all get used up. This is not the case with a tankless water heating unit.

When you will turn on a faucet a heat exchanger will heat water. The water will be delivered based on the gallon per minute capacity of the unit. This is why a tankless unit takes longer to supply hot water. 50 gallons of heated water is stored in the tank whether you use it or not.

If the water keeps standing for long the heat dissipates causing energy loss. Moreover standing water can become dirty due to microorganisms‘ growth.

Replacing the 50-gallon Traditional Water Heater

To replace a traditional heater of 50 Gallons you will have to consider the following things.

  • 10 GPM capacity gas unit or 27 kW electric unit is if you want to install the unit in a cold climate.
  • 7 GPM gas tankless water heater or 18 kW electric unit if the climate is warm and groundwater temperature higher.

Similarly, you can estimate the size of the tankless water heater you need to replace your 60, 70, or 80-gallon water heater.

The above rough estimate gives you an idea about what size water heater you need. To be more accurate about the size ask a local contractor for a better recommendation. Due to their long-term experience, they will give you an accurate number which you can buy from any nearby store or online.

We hope that after going through this handy guide you must have cleared your mind about the confusing question “What size tankless water heater to replace a 50-gallon traditional water heater.”

If you still have any confusion in your mind you can comment below or call your nearest plumbing service providers.

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Adam Miller

With years of experience under his belt, Adam decided to put his water heater knowledge to work. By providing high-quality content and expert guides, Adam hopes to help anyone looking for expert water heater advice.