Sizing a Tankless Water Heater – How to Choose the Right Size for Your Home

When it comes to choosing a water heater for your home, tankless options have become increasingly popular. Unlike traditional tank water heaters, tankless water heaters provide hot water on demand, eliminating the need for a large storage tank. However, it’s important to properly size a tankless water heater to ensure it can meet the needs of your household.

One of the key factors to consider when sizing a tankless water heater is the flow rate. The flow rate refers to the amount of hot water needed at any given time, and it is measured in gallons per minute (GPM). To determine the flow rate that your tankless water heater should be able to handle, you need to consider the number of fixtures that will be using hot water simultaneously.

For example, if you have a shower with a flow rate of 2 GPM and a kitchen faucet with a flow rate of 1.5 GPM, the total flow rate would be 3.5 GPM. Therefore, you would need a tankless water heater that can handle a flow rate of at least 3.5 GPM to provide hot water to both fixtures simultaneously.

Another important aspect to consider when sizing a tankless water heater is the temperature rise. The temperature rise refers to the difference between the desired hot water temperature and the temperature of the cold water entering the heater. The higher the desired hot water temperature and the colder the incoming water, the larger the temperature rise.

To calculate the temperature rise, subtract the incoming water temperature from the desired hot water temperature. For example, if the incoming water temperature is 50 degrees Fahrenheit and the desired hot water temperature is 120 degrees Fahrenheit, the temperature rise would be 70 degrees Fahrenheit. This information is crucial for determining the size and capacity of the tankless water heater needed.

Choosing the Right Size for a Tankless Water Heater

When it comes to purchasing a tankless water heater, one of the most important factors to consider is choosing the right size. The size of a tankless water heater determines its capacity to provide hot water, and it is crucial to select a size that can meet the hot water demands of your household.

To determine the right size for a tankless water heater, you need to consider two main factors: the flow rate and the temperature rise. The flow rate refers to the amount of hot water that you need at any given time, while the temperature rise is the difference between the incoming cold water temperature and the desired hot water temperature.

The flow rate can vary depending on your household’s hot water usage. For example, if you have multiple bathrooms and appliances that require hot water simultaneously, you will need a higher flow rate. On the other hand, if you have fewer water outlets or if hot water usage is limited, you can opt for a lower flow rate.

The temperature rise depends on the climate and the hot water temperature you desire. In colder climates, the incoming water temperature is lower, requiring a higher temperature rise. Conversely, in warmer climates, the incoming water temperature is higher, resulting in a lower temperature rise.

Once you have determined both the flow rate and the temperature rise, you can use these values to select the appropriate size for a tankless water heater. You can consult the manufacturer’s specifications, which usually provide a flow rate chart that matches different temperature rise values.

It is important to note that undersizing a tankless water heater can lead to insufficient hot water supply, while oversizing can be unnecessary and costlier. Therefore, it is crucial to accurately calculate the flow rate and temperature rise to select the right size that can effectively meet your household’s hot water needs.

Consulting with a professional plumber can also be beneficial in determining the right size for a tankless water heater. A plumber can assess your household’s hot water demands and provide expert advice on selecting the appropriate size that ensures optimal performance and energy efficiency.

In conclusion, choosing the right size for a tankless water heater involves considering the flow rate, temperature rise, and hot water demands of your household. Accurately calculating these factors and consulting with a professional plumber can help you make an informed decision and ensure that your tankless water heater can effectively supply hot water throughout your home.

Understanding Your Hot Water Needs

Before sizing a tankless water heater, it’s important to have a good understanding of your hot water needs. This includes taking into account the number of individuals in your household, their daily routines, and the appliances and fixtures that require hot water.

First, consider the number of individuals in your household. A smaller household with only a few people will generally have lower hot water demand compared to a larger household with multiple family members.

Next, think about the daily routines of the individuals in your household. Are there multiple showers being taken at the same time in the morning? Do you frequently run the dishwasher or the washing machine throughout the day? These activities can greatly affect your hot water usage.

Also, consider the appliances and fixtures that require hot water. In addition to showers, typical appliances and fixtures that use hot water include sinks, tubs, washing machines, dishwashers, and even outdoor faucets. Each of these will add to your overall hot water demand.

Once you have a good understanding of your hot water needs, you can start to determine the appropriate size of a tankless water heater. The size you choose will depend on factors such as flow rate, temperature rise, and the number of hot water outlets you need to supply simultaneously. It’s recommended to consult with a professional plumber or use online sizing calculators to ensure you select the right size for your specific needs.

Calculating the Flow Rate

To properly size a tankless water heater, you need to calculate the flow rate, which is measured in gallons per minute (GPM). The flow rate is the amount of hot water the heater can supply at a given moment, and it is determined by the water demand in your household.

To calculate the flow rate, you need to consider the number of fixtures and appliances that require hot water simultaneously. For example, if you have a shower, a dishwasher, and a washing machine running at the same time, you would need a higher flow rate compared to a household that only has one fixture in use.

To estimate the flow rate, you need to determine the average GPM of each fixture or appliance. This information can usually be found in the product specifications or by consulting with the manufacturer.

Once you have the average GPM for each fixture, add them together to get the total flow rate required at any given time. It’s important to consider the peak demand, as this is when the flow rate will be at its highest.

Keep in mind that the flow rate will also depend on the temperature rise, which is the difference between the incoming cold water temperature and the desired hot water temperature. A higher temperature rise will result in a lower flow rate, as the heater needs to work harder to heat the water to the desired temperature.

By accurately calculating the flow rate, you can ensure that your tankless water heater is sized appropriately for your household’s hot water needs. This will help prevent any issues with insufficient hot water supply and ensure optimal performance and energy efficiency.

Considering Incoming Water Temperature

One important factor to consider when sizing a tankless water heater is the incoming water temperature. The incoming water temperature refers to the temperature of the water as it enters the water heater. In colder regions, the incoming water temperature is typically lower than in warmer regions.

The colder the incoming water temperature, the more energy the tankless water heater will need to heat the water to the desired temperature. This means that in colder regions, a larger tankless water heater may be needed to meet the hot water demand of a household.

To determine the appropriate tankless water heater size based on incoming water temperature, the temperature rise needs to be calculated. The temperature rise is the difference between the desired hot water temperature and the incoming water temperature. For example, if the desired hot water temperature is 120 degrees Fahrenheit and the incoming water temperature is 50 degrees Fahrenheit, the temperature rise would be 70 degrees Fahrenheit.

The tankless water heater’s flow rate also needs to be considered when sizing for incoming water temperature. The flow rate is the amount of hot water the tankless water heater can produce per minute. Different models of tankless water heaters have different flow rates. It is important to choose a tankless water heater that can provide enough hot water for the household’s needs, taking into account the temperature rise and the desired hot water temperature.

In conclusion, considering the incoming water temperature is crucial when sizing a tankless water heater. The colder the incoming water temperature, the larger the tankless water heater needed to meet hot water demand. Calculating the temperature rise and considering the flow rate are important factors in finding the right tankless water heater size for a household.

Accounting for Peak Demand

When sizing a tankless water heater, it is crucial to take into account the peak demand of hot water in your household. Peak demand is the maximum amount of hot water that may be used simultaneously at any given time. Estimating the peak demand can help ensure that your tankless water heater can meet the hot water needs of your household.

One way to calculate the peak demand is to consider the number of fixtures or appliances that may be running hot water at the same time. For example, if you have a household with a shower, a dishwasher, and a washing machine, you would need to account for the potential simultaneous use of these fixtures.

It is important to note that different fixtures or appliances have different flow rates, which can impact the peak demand calculation. For instance, a shower typically has a flow rate of 2-2.5 gallons per minute (GPM), while a dishwasher may have a flow rate of around 1.5-2 GPM. By considering the flow rates of each fixture or appliance, you can determine the total hot water demand during peak usage.

In addition to considering fixtures and appliances, it is also important to factor in the desired hot water temperature. A tankless water heater must be able to heat the water to the desired temperature at the peak demand. If the desired temperature is higher, the tankless water heater may need to work harder and may have a lower flow rate.

It is advisable to consult a professional plumber or a tankless water heater manufacturer to accurately determine the peak demand and size the tankless water heater accordingly. They will consider factors such as the number of fixtures, flow rates, desired temperature, and other factors specific to your household.

By accounting for peak demand, you can ensure that your tankless water heater provides an optimal supply of hot water for your household’s needs, without running into issues such as inadequate hot water or an insufficient flow rate.

Reviewing the Available Tankless Water Heater Options

When it comes to selecting a tankless water heater, there are several options available to choose from. Each option has its own unique features and benefits, so it’s important to consider your specific needs before making a decision.

1. Electric Tankless Water Heaters: These units are powered by electricity and provide on-demand hot water without the need for a storage tank. They are generally more energy-efficient than traditional water heaters and are suitable for smaller households with low to moderate hot water demands.

2. Gas Tankless Water Heaters: These units are powered by natural gas or propane and offer a high flow rate and quick heating. They are a popular choice for larger households with higher hot water demands. Gas tankless water heaters require proper ventilation and a gas hookup.

3. Whole-House Tankless Water Heaters: As the name suggests, these units are designed to provide hot water to the entire house. They have a higher flow rate and can handle multiple hot water demands simultaneously. They are more expensive and require professional installation due to their higher capacity requirements.

4. Point-of-Use Tankless Water Heaters: These units are installed near the point of use, such as under a sink or in a bathroom. They provide instant hot water to a specific location and are ideal for small-scale applications. Point-of-use tankless water heaters are less expensive and easier to install.

It’s important to consider factors such as your household size, hot water demand, available energy sources, and budget when choosing a tankless water heater. Consulting with a professional plumber or water heater specialist can help you determine the right size and type of tankless water heater for your specific needs.

Consulting with a Professional

While this article provides a general overview of how to size a tankless water heater, it’s important to consult with a professional before making any final decisions. A licensed plumber or HVAC technician will have the knowledge and expertise to properly assess your specific needs and recommend the appropriate size for your home.

A professional will take various factors into consideration when determining the right size tankless water heater for your home, including the number of bathrooms, peak hot water demand, and the temperature rise required. They will also consider any additional factors such as the flow rate of your fixtures, the distance of the water heater from the point of use, and the layout of your plumbing system.

By consulting with a professional, you can ensure that you select a tankless water heater that meets your household’s hot water needs, while also optimizing energy efficiency and avoiding any potential issues. They can provide you with accurate calculations and recommend the best brand and model based on their industry knowledge and experience.

Investing in a properly sized tankless water heater will not only provide you with a reliable and continuous supply of hot water, but it can also save you money on energy bills in the long run. So, don’t hesitate to reach out to a professional to help you make an informed decision and enjoy the benefits of a tankless water heater in your home.

Video:

EVERYTHING about Electric Tankless Water Heaters (2018)

3 Things They Don’t Tell You About Tankless

Photo of author

Ryan Pietrzak

Ryan Pietrzak, a licensed plumber with 12+ years of experience, is the trusted expert behind Plumbing.Academy. With a wealth of practical knowledge, Ryan guides you through plumbing challenges, making informed decisions easier. His reputable advice, rooted in real-world expertise, empowers both DIY enthusiasts and seasoned plumbers.