Choosing the right size for your tankless water heater is essential to make sure your home has a continuous supply of hot water. A properly sized unit can save energy, reduce costs, and provide consistent comfort without overburdening the system or running out of hot water during peak usage times.
In this guide, we will help you determine the appropriate tankless water heater size by breaking down factors like recovery rate, energy efficiency, cost, and simultaneous hot water usage.
By following this guide, you’ll have a better understanding of what to look for and how to make sure the tankless water heater you choose is perfect for your home’s needs.
Recovery Rate and Hot Water Usage
The recovery rate of a tankless water heater refers to the amount of hot water the unit can provide in an hour after being completely drained. This is essential for homes with high hot water demands, such as those with multiple bathrooms or large households. The recovery rate helps guarantee that the system can keep up during times of peak usage, like in the mornings or evenings when multiple family members might need hot water at once.
To determine the appropriate recovery rate, consider factors such as:
- The number of people in your household
- The number of bathrooms and showers
- How often you use hot water simultaneously across multiple fixtures
For example, a small household with one bathroom and one or two people might be satisfied with a tankless water heater offering a low recovery rate. However, a larger family with several bathrooms may need a tankless water heater that delivers a higher recovery rate to ensure consistent hot water for everyone. The table below outlines general recommendations for recovery rates based on household size:
- 1–2 people (1–1.5 bathrooms): 4–6 gallons per hour (GPH)
- 3–4 people (1.5–2.5 bathrooms): 6–9 GPH
- 5+ people (2.5+ bathrooms): 9+ GPH
By selecting a unit that meets your household’s needs, you’ll never run out of hot water even during peak usage.
Uniform Energy Factor (UEF) and Energy Efficiency
Another critical factor in determining the right tankless water heater size is its energy efficiency, typically measured using the Uniform Energy Factor (UEF) rating. The UEF measures how efficiently a unit converts energy into hot water. The higher the UEF rating, the more efficient the water heater is.
Energy Star-certified water heaters generally have UEF ratings ranging from 0.65 to 0.95. Whereas, heat pump water heaters boast even higher UEF ratings of 2.75 to 3.5. Choosing a unit with a higher UEF rating can save you money on energy bills over time and contribute to reducing your home’s carbon footprint.
For homeowners prioritizing energy efficiency, opting for a tankless water heater with a higher UEF rating can result in long-term savings and a more environmentally friendly option.
Cost Comparison: Conventional vs. Heat Pump Water Heaters
When choosing the size of your tankless water heater, cost considerations go beyond the upfront price. While conventional water heaters typically have a lower purchase price, their long-term operating costs may be higher due to less efficient energy consumption. On the other hand, heat pump water heaters have a higher initial cost but are far more energy-efficient for long-term savings.
- Conventional water heaters have a lower purchase price but typically higher energy bills.
- Heat pump water heaters may cost more upfront but have lower operating costs. They provide more savings over time due to their efficiency.
Additionally, many utility companies offer rebates for energy-efficient water heaters, including heat pump models. When considering the cost of a new water heater, it’s essential to factor in both the initial purchase price and the long-term energy savings.
Warranty Considerations
When selecting a tankless water heater, it’s important to look at the warranty offered by the manufacturer. A longer warranty generally indicates greater confidence in the product’s reliability and durability.
- Conventional water heaters often come with a 6-year warranty, with a typical lifespan of 10–15 years.
- Heat pump water heaters usually come with a 10-year warranty, reflecting their durability and longer lifespan.
Considering the warranty helps ensure that your investment is protected and provides peace of mind that the water heater will last for many years without issues.
Understanding Tankless Water Heater Mechanism
Unlike traditional storage water heaters, tankless water heaters don’t store hot water. Instead, they heat water on-demand as it flows through the system. When you turn on a hot water tap, cold water enters the tankless unit. This is where it is heated by either a gas burner or an electric heating element. The system’s electronic control unit assists in making sure the water temperature remains consistent throughout its usage.
Advantages of tankless water heaters include:
- Endless hot water: You’ll never run out of hot water as long as the unit can meet your household’s demand.
- Energy efficiency: By only heating water when needed, tankless models significantly reduce energy consumption compared to traditional storage tank models.
- Space savings: The compact design allows them to be mounted on walls and free up floor space.
- Longevity: Tankless models often last up to 20 years or more with proper maintenance.
Flow Rate and Temperature Rise
Properly sizing a tankless water heater depends on the flow rate and temperature rise. The flow rate is the amount of water that needs to be heated at any given time. It is typically measured in gallons per minute (GPM). The temperature rise is the difference between the incoming cold water temperature and the desired output temperature.
For example, if the incoming water is 50°F and you need it to be 120°F, the required temperature rise is 70°F. You’ll need to choose a tankless water heater that can provide this rise at the required flow rate. Here’s a general guideline:
- 2 GPM: Requires a 35°F temperature rise
- 3 GPM: Requires a 30°F temperature rise
- 4 GPM: Requires a 25°F temperature rise
By calculating the necessary flow rate and temperature rise, you can determine the size of the tankless water heater that’s right for your home.
Step-by-Step Sizing Process
To accurately size a tankless water heater, follow these steps:
- Determine your home’s hot water demand: List all the fixtures (showers, sinks, appliances) and their flow rates. Consider the maximum number of fixtures you expect to use simultaneously.
- Calculate the required temperature rise: Subtract the incoming water temperature from the desired output temperature.
- Compare available models: Look at different tankless water heater models and their specifications to find a unit that can handle both the flow rate and temperature rise for your home.
For example, if you want to run two showers simultaneously and each has a flow rate of 2.6 GPM, the total flow rate needed would be 5.2 GPM. If the required temperature rise is 65°F, you would need a tankless water heater capable of handling these requirements.
NaviSizer: A Tool for Accurate Sizing
The NaviSizer tool from Navien helps you determine the appropriate size for your tankless water heater. By inputting the number of fixtures, their flow rates, and the desired temperature rise, NaviSizer will recommend the correct size to meet your household’s hot water needs. This tool eliminates guesswork and helps you choose the right unit for maximum efficiency.
Replacing a Traditional Water Heater with a Tankless Water Heater
When replacing a traditional water heater with a tankless system, it’s essential to consult with a licensed plumbing professional. Unlike traditional models, which are sized based on storage capacity, tankless systems are sized by flow rate. Consulting an expert will help you avoid under-sizing or over-sizing the unit.
Benefits of Properly Sizing a Tankless Water Heater
Properly sizing your tankless water heater offers numerous benefits:
- Energy efficiency: The unit operates at optimal capacity, reducing unnecessary energy consumption.
- Cost savings: You avoid the additional costs of an oversized unit or the inefficiencies of an undersized one.
- Consistent hot water: You’ll enjoy a continuous supply of hot water without interruptions during peak usage.
- Longer lifespan: The right size water heater will operate more efficiently and last longer.
Sizing Recommendations for Household Needs
Here are some general guidelines for sizing a tankless water heater based on the number of simultaneous fixtures:
- 1–2 fixtures: A flow rate of 3.5 GPM is typically sufficient.
- 2–3 fixtures: A flow rate of 5 GPM may be needed.
- 3–4 fixtures: Consider a flow rate of 7 GPM.
These recommendations provide a rough estimate, but actual needs may vary depending on your household’s usage patterns.
Choosing the right size tankless water heater is important for establishing a continuous supply of hot water, enhancing energy efficiency, and saving on long-term costs. For professional guidance and installation, trust Water Heaters Now. Our team can help you choose the ideal tankless water heater and provide a smooth installation process for your home. Contact us today to schedule your consultation and enjoy the benefits of an efficiently sized and expertly installed tankless water heater.
