Back to blogs

Deciding What Size Tankless Water Heater You Need: Our Guide

When it comes to providing your home with an endless stream of hot water, tankless water heaters stand out for their efficiency and space-saving design. Yet, the question we often encounter is "what size tankless water heater do I need?" Knowing that too small a unit can lead to a chilly inconvenience and too large could mean unspent dollars, we understand that sizing is paramount. Our goal is to arm you with the knowledge to make an informed decision. Throughout this tankless water heater buying guide, we'll touch on the pivotal considerations necessary for choosing the right tankless water heater for your needs.

The first step involves looking at the intricate dance between the flow rate of your household fixtures and the temperature rise needed from your water heater. We'll explore how these factors shouldn't be guessed but calculated with precision for peak performance year-round. Join us as we delve into the world of gallons per minute (GPM) and degrees Fahrenheit, and transform complexity into clarity.

Key Takeaways

  • Determine the correct tankless water heater size matching your household's needs.
  • Understand the significance of assessing both flow rate and temperature rise.
  • Learn how a proper size prevents overload and extends the life of the heater.
  • Utilize specialized tools like NaviSizer for expert recommendations.
  • Consider professional advice when transitioning from a traditional tank heater.
  • Appreciate the nuances of water heating during different seasons.

Understanding the Importance of Correct Water Heater Sizing

Appreciating the complexities of hot water needs for your home starts with one critical question: "what size water heater is right for me?" Accurate tankless water heater sizing is not only about comfort but about efficiency and economy. An undersized water heater will struggle to deliver the hot water your household demands, leading to potential discomfort and unit strain. Conversely, an oversized unit may cycle inefficiently, leading to wasted energy and increased operational costs. The key to unlocking the full benefits of your investment lies in how to determine tankless water heater size fitting your specific needs.

We recognize that pinpointing the precise size is imperative. For this reason, our approach to sizing is twofold—considering both the flow rate and temperature rise. Navien's innovative tool, NaviSizer, simplifies this process. It adeptly matches your home's demands with the ideal Navien water heater, assuring that your selection is neither too modest nor excessively substantial.

To facilitate a clear understanding, we have prepared a table to guide you through the process of assessing your flow rate and temperature rise, thus ensuring you select a Navien tankless water heater that can handle the demands of your residence:

Fixture Flow Rate (GPM) Common Usage Scenario Shower 2.5 GPM Hot: 104°F / Cold: 60°F Kitchen Sink 1.5 GPM Hot: 110°F / Cold: 60°F Bathroom Sink 1.0 GPM Moderate Use: Morning and Evening Peaks Dishwasher 1.5 GPM Hot: 110°F / Cold: 60°F Washing Machine 2.0 GPM Hot: 120°F / Cold: 60°F Tub 4.0 GPM Hot: 102°F / Cold: 60°F

Consider the above flow rates as a general estimation. You should calculate your home's flow rate needs by adding the flow rates of fixtures that might run simultaneously. Once the total expected flow rate is calculated, correlating it with the necessary temperature rise at the coldest time of year will yield the most accurate indication of the appropriate tankless water heater size for your home.

In our experience, the importance of rigorous sizing cannot be overstated—it is the backbone of functional efficiency and economic operation in your daily life. By diligently analyzing your tankless water heater sizing, we assure you of optimal performance and satisfaction. Trust us to guide you through each step, ensuring that you never skip a beat when it comes to uninterrupted, cost-effective hot water access.

How Flow Rate Affects Tankless Water Heater Size

When we embark on the task of sizing a tankless water heater for our homes, often the first metric we encounter is the flow rate. This measure is critical as it dictates the volume of hot water that can be delivered at any given time. The flow rate, expressed in gallons per minute (GPM), directly influences the tankless water heater capacity calculation. Our main objective is to ensure that our chosen model aligns with the simultaneous hot water needs of our household.

Calculating Your Home's Hot Water Demand

To determine the right size for your tankless water heater, it's essential to calculate the cumulative flow rate based on the simultaneous usage of all hot water fixtures. This calculation, often facilitated by a tankless water heater calculator, helps us understand the demands we are placing on the unit. Whether you're running just a shower or multiple appliances at once, calculating the collective flow rate is a step we cannot afford to skip.

The Role of Simultaneous Fixture Use

Imagine you're starting your day with a morning shower while another family member is washing dishes in the kitchen. The likelihood of running multiple fixtures at the same time is high in most households. For this reason, we consider not just the flow rate of individual fixtures, but their combined rates when used simultaneously. With tools like the water heater sizing chart, we can effectively judge what our true GPM requirement is and thereby select a tankless water heater with the appropriate capacity.

  • Shower usage typically demands around 2.5 GPM.
  • A running faucet adds approximately 0.75 GPM to the demand.
  • To ensure a warm shower and a hot sink simultaneously, a minimum of a 3.26 GPM capacity is ideal.

Our benchmarks suggest that for 1-2 simultaneous fixtures, such as the aforementioned scenarios, a tankless water heater should support at least 3.5 GPM. However, for more substantial demands such as 2-3 simultaneous fixtures, we should consider systems that can deliver 5 GPM, and when we scale up to 3-4 fixtures, the capacity should extend to at least 7 GPM. While these figures are guidelines, our specific usage patterns might dictate a slight adjustment of these values.

To put it into perspective, let's look at a typical scenario with a water heater sizing chart:

Fixture Flow Rate Shower 2.5 GPM Kitchen Sink 1.5 GPM Washing Machine 2.0 GPM High Use (e.g., Multiple Showers) > 5 GPM

It's important to align our tankless water heater's size with our actual needs, as undersizing may hinder our daily routines and oversizing could mean an unnecessary investment. By applying careful analysis to the tankless water heater capacity calculation, we can cater beautifully to the dance of daily life, balancing efficiency with uninterrupted access to the warmth of running hot water.

Temperature Rise: A Key Component in Water Heater Sizing

When we discuss tankless water heater sizing, one factor that stands out for its critical role is temperature rise. This is the differential between the incoming cold water temperature and your desired hot water temperature. A precise temperature rise calculation is essential to ensure that your tankless water heater can cope with the peak demands of cold weather, providing consistent and comfortable hot water throughout the year.

For those of us living in regions with significant seasonal temperature swings, accurately estimating temperature rise is particularly important. In winter, when the inlet water temperatures can plummet, the tankless water heater must work harder to achieve the desired warmth. Sizing your unit correctly by accounting for the coldest temperatures ensures that even on the chilliest days, your showers will be warm and your dishes clean.

Here's how the temperature rise affects the sizing:

  • Higher Temperature Rise Needed for Colder Climates: In places with colder incoming water temperatures, the heater must be able to accommodate a higher temperature rise.
  • Optimal Performance: Sizing with correct temperature rise ensures efficient operation, meaning you're likely to experience fewer fluctuations in water temperature during use.
  • Maximizing Lifespan: Accurate temperature rise calculation prevents unit overload, preserving the longevity of your tankless water heater.

Consider this example to illustrate the importance of temperature rise in tankless water heater sizing:

Incoming Water Temperature Desired Set Temperature Temperature Rise 50°F (Winter Average) 120°F 70°F 70°F (Summer Average) 120°F 50°F

As shown in our table, the required temperature rise in winter is substantially higher than in summer. Undersizing based on milder conditions could leave you in the cold when winter arrives. Our focus must, therefore, include the anticipated worst-case scenario to ensure comfort and efficacy all year round.

We must account for every facet of our water heating demands to optimize our tankless water heater's performance. Understanding the significance of the temperature rise is a key part of the puzzle—a concept we're committed to demystifying for our users. This diligent approach to sizing prevents the common pitfalls of underestimating our heating needs and secures a reliable stream of hot water tailored to our household’s unique requirements.

Factors Affecting Temperature Rise and Flow Rate

In examining the sizing of tankless water heaters, we observe that not all factors are constant. Two critical variables are the seasonal variations in water temperature and the effects of inlet water temperature. These important considerations bear a profound influence on the heater's ability to rise to the occasion and deliver hot water consistently during times of colder seasons.

Seasonal Variations and Inlet Water Temperature

As seasons change, so does the temperature of the water entering our homes. This phenomenon substantially impacts the temperature rise capability of tankless water heaters. During chillier seasons, our calculations for sizing must include the required greater temperature rise to compensate for the decreased inlet water temperature. Let's delve deeper into how these factors interplay to influence our tankless water heater's efficiency.

  • In winter, the inlet water temperature can plummet, necessitating a higher temperature rise.
  • The heater must compensate for the lower starting temperature to achieve the desired output.
  • Evaluating the lowest average inlet water temperatures is key to proper sizing.

Understanding these shifts is crucial for those of us who experience significant temperature fluctuations throughout the year. It ensures that, despite the lowering temperatures outside, we have ample hot water inside.

To provide a clearer picture, we've put together a table illustrating typical variations in inlet water temperatures throughout the year and their implications:

Season Average Inlet Water Temperature Required Temperature Rise Effects on Heater Sizing Spring 60°F 60°F Medium-sized heater required Summer 70°F 50°F Smaller heater may suffice Fall 55°F 65°F Medium to large heater required Winter 40°F 80°F Larger heater necessary

This table demonstrates the necessity of a powerful heater in winter versus a potentially less robust system in summer. We emphasize that proper planning and sizing are essential to ensure your tankless water heater is not taxed beyond its capabilities. By preparing for the coldest of days, we safeguard against inefficiencies that may arise from unanticipated demand spikes, thereby guaranteeing uninterrupted access to hot water throughout all seasons.

Comparing Types of Tankless Water Heaters

When it comes to ensuring a constant supply of hot water in our homes, the importance of selecting the right tankless water heater is undeniable. We must carefully assess the types of tankless water heaters available, understanding that each type brings its own set of benefits and specifications to meet various hot water needs. In this section, we'll contrast gas and electric tankless water heaters to aid you in making an informed decision for your home.

To set the scene, let's imagine the diverse range of households and the multitude of daily hot water tasks—we have high-demand showers, energy-efficient dishwashers, and the all-important kitchen sinks. Each of these plays a vital role in our home's ecosystem and it's paramount that our chosen tankless water heater can keep pace.

Gas vs. Electric Tankless Water Heaters: Understanding the Differences

Gas tankless water heaters are lauded for their sizeable temperature rise per GPM, which can be particularly advantageous in colder climates or for homes with high hot water demands. On the other hand, electric tankless water heaters are often celebrated for their smaller size and ease of installation, making them suitable for smaller spaces and average hot water needs.

Let us delve deeper and present a comprehensive comparison table that reflects the nuances between these two prevalent types of tankless water heaters:

Characteristic Gas Tankless Water Heaters Electric Tankless Water Heaters Energy Source Natural gas or propane Electricity Temperature Rise Capability Higher capacity for temperature rise per GPM Lower capacity for temperature rise per GPM Installation May require venting, complex installation Typically easier, more flexibility in placement Operational Cost Often lower due to gas efficiency Can be higher, depending on electricity rates Environmental Impact Lower emissions with newer models Dependent on electricity source (renewable vs. non-renewable) Lifespan Generally longer with proper maintenance Varies based on usage and model quality Initial Investment Typically higher due to installation requirements Lower upfront costs

In our pursuit of optimal water heating solutions, we must also consider the energy source availability in our area, the upfront investment we are willing to make, and the long-term running costs. As we compare these aspects, we aim to empower you with knowledge, enabling a wise decision that resonates with not just your immediate needs but also your long-term considerations.

With the insights provided in the above table, our journey through selecting the ideal tankless water heater becomes clearer. Whether you lean towards the robust performance of a gas model or the eco-conscious, sleek design of an electric unit, your decision will ultimately align with your household's unique hot water needs and lifestyle preferences.

How to Calculate Size Replacing a Traditional Tank Heater

Many homeowners choose to replace tank water heater with tankless units to take advantage of the increased efficiency and space-saving benefits. However, successful tankless water heater conversion is contingent on proper sizing. Unlike traditional tank heaters, tankless units aren't rated by capacity but by the rate of hot water flow they can provide, measured in gallons per minute (GPM).

Therefore, to determine the correct tankless unit when replacing a traditional water heater, the equivalent exchange based on storage capacity is irrelevant. What matters is how much hot water you require at peak times and whether the new tankless model can handle this flow rate while achieving the desired temperature rise.

Finding the Right Size for Your Tankless Water Heater Conversion

We always recommend consulting with a licensed plumber who can assess your hot water needs accurately. The plumber will calculate the total GPM required at peak times by summing up the flow rates of all the fixtures you may use simultaneously. Then, factoring in the temperature of the incoming cold water, they will help you determine the necessary temperature rise and, consequently, the suitable GPM rating for your new tankless water heater.

Here's a simplified example of the process:

  1. List all major hot water fixtures in your home (e.g., showers, washing machines).
  2. Note the average flow rates for these fixtures (in GPM).
  3. Add up these flow rates to find your total GPM requirement at peak usage.
  4. Consult historical data to find the coldest incoming water temperature for your area.
  5. Subtract this temperature from your desired hot water temperature to find the required temperature rise.
  6. Select a tankless water heater model with a GPM rating that can handle this temperature rise.

By following this method, you ensure that your tankless water heater conversion will meet your hot water needs without the risk of undersizing.

Flow Rate and Temperature Rise Illustration

To illustrate how flow rate and temperature rise factor into the sizing process, we've constructed the following table:

Hot Water Fixture Flow Rate (GPM) Peak Simultaneous Use Temperature Rise (∆T) Shower 2.1 Morning or Evening Your area's specific needs Sink 1.0 Dishwasher 1.2

This table helps you visualize the importance of adding the flow rates of all fixtures used concurrently to ascertain the household's total GPM usage. Remember, this total flow rate must be sustainable by your new tankless water heater at the required temperature rise unique to your locality and usage patterns.

Fortunately, the specialized knowledge of licensed plumbing professionals can guide you through every step of your tankless water heater conversion, ensuring no detail is overlooked. Their expertise will facilitate a seamless transition from your old tank to a new, efficient, tankless water heating system, providing a steady flow of hot water suited to your specific needs.

tankless water heater conversion guide

Tankless Water Heater Capacity Calculation

As we navigate the intricacies of home heating, a crucial element in our toolkit is understanding the BTU input necessary for a tankless water heater. BTU, or British Thermal Unit, is the traditional unit of energy equal to about 1,055 joules. In the context of tankless water heaters, BTU input measures the amount of gas energy fed into the unit to heat the water efficiently. The BTU input tankless water heater specification directly correlates with the heater's ability to raise the temperature of the water and the flow rate at which it can produce hot water.

Understanding BTU Input and Its Impact on Sizing

When it comes to determining the right tankless water heater size for our homes, the BTU input is of paramount importance. A model with a high BTU input can heat more water faster, which means it can provide a more significant hot water flow rate to meet demands during peak usage. However, we must align our choice with the specific requirements of our household to avoid unnecessary expense and potential inefficiency.

To further elucidate the importance of BTU input and its relationship to water heater capacity, consider the following table:

BTU Input Max Flow Rate (GPM) Typical Usage 120,000 BTUs 3.5 Small to medium-sized homes, fewer simultaneous fixtures 180,000 BTUs 5.0 Medium-sized homes, several simultaneous fixtures 199,000 BTUs 7.0 Large homes with high hot water demand

This table showcases the potential flow rate at different BTU inputs under standard conditions, giving us a snapshot of water heater capacity BTUs. Knowing this, we can make an informed decision that balances operational cost against hot water requirements. Additionally, matching our water heater's BTU input to our home's size and hot water usage patterns aids in achieving the most energy-efficient outcome.

It's essential to remember that the listed flow rates are approximate and can be affected by the specific conditions present in our homes; such as the number of inhabitants, frequency and concurrency of hot water use, and seasonal temperature variations.

  • A higher BTU input implies a tankless water heater with greater capacity for heating and delivering more water.
  • Selecting a unit with a BTU input that aligns with the actual hot water usage prevents energy waste and maximizes efficiency.
  • Calculating the peak hot water usage is critical to determining the BTU input necessary for your home.

A step that is often overlooked in the process of sizing is the consideration of maximum needs—not just everyday usage. Consider holiday gatherings or times when guests are home; moments of peak use could put a strain on a system that is sized merely for average conditions.

In sum, by applying a precise calculation of BTU input against our home's demands, we ensure a seamless supply of hot water—adequate for simultaneous use across all fixtures—without overburdening our systems or our wallets. Through a thoughtful approach to tankless water heater capacity calculation, we provide not just comfort and convenience but also uphold the energy efficiency that tankless water heaters are celebrated for.

Using a Tankless Water Heater Sizing Chart

When it's time to upgrade to a tankless water heater or replace an aging unit, knowing the right size for your home is crucial. A tankless water heater sizing chart becomes an indispensable tool for this purpose. It allows you to calculate the size based on your home's peak hot water demands, measured as flow rate in gallons per minute (GPM), and the required temperature rise. This ensures that the unit you choose will not only provide hot water efficiently but also operate cost-effectively over its lifespan.

We understand that selecting the right tankless water heater is more than an investment—it's a commitment to your home's comfort and efficiency. For this reason, we encourage you to use our water heater GPM chart to understand the relationship between flow rates of various home appliances and your optimal unit size. Here’s an example to illustrate how this tool can be utilized:

Fixture Type Flow Rate (GPM) Typical Temperature Rise (ΔT) Standard Shower 2.1 55°F High-Efficiency Showerhead 1.5 55°F Kitchen Faucet 1.0 45°F Dishwasher 1.5 45°F Washing Machine 2.0 45°F

Using the chart above as a point of reference and considering each potential point of usage, add up the flow rates of all fixtures that might be used simultaneously. This will give you an aggregate demand figure. The temperature rise, or ΔT, is the difference between the incoming cold water temperature and the set output temperature of your tankless water heater. For most households, a temperature set point of around 120°F is common.

After establishing the total flow rate and desired temperature rise, it's easier to determine which tankless water heater models meet your needs. Using a tankless water heater sizing chart can mitigate the risk of purchasing a unit that's too small, leading to a never-ending game of hot water roulette, or a unit that’s too large, resulting in unnecessary energy consumption.

Below is a water heater GPM chart for a rough estimate of various household sizes:

Household Size Estimated Required GPM Suggested Temperature Rise (ΔT) 1-2 people Up to 3.5 GPM 55°F-60°F 2-3 people 3.5 to 5.0 GPM 60°F-65°F 3-4 people 5.0 to 7.0 GPM 65°F-70°F 4+ people Over 7.0 GPM 70°F+

Remember, these charts are guides to get you closer to the right choice. For precise sizing, particularly for larger homes or areas with significant temperature variance, consulting with a licensed professional may be the best course of action. They can assist you with specific calculations, taking into account local climate conditions and unique home water usage behaviors, to ensure the tankless water heater you select is perfect for your household's needs.

Navigating Tankless Water Heater Sizing for Large Households

For those of us with larger homes, ensuring that everyone has access to hot water when needed can be a challenge. When considering large household tankless water heater sizing, it's not just about picking the largest unit available; it's about finding the size that meets high demand without wasteful oversizing. Let's delve into the key considerations for high demand water heater size to maintain efficiency and satisfaction.

  • Assessing the high demand of simultaneous fixture use
  • Calculating the flow rate necessary for the whole household
  • Addressing the unique sizing requirements for larger homes

Fixture Flow Rate (GPM) Average Usage Multiple Showers 5.0 - 7.5 High Several Sinks 2.0 - 3.0 High Appliances (Dishwashers, Washers) 3.0 - 4.5 Variable Total Demand 10.0 - 15.0 Peak Times

We understand that large households operate on a different scale. Preparing breakfast while someone's in the shower, running the dishwasher, or doing laundry are everyday tasks that can coincide. This necessitates a tankless water heater sizing that can manage such a high demand water heater size to deliver a steady flow of hot water across multiple fixtures.

  1. Identify peak hot water usage times and patterns in your home.
  2. Determine the maximum flow rate needed during these peak times.
  3. Consult with a licensed plumber for a precise sizing and installation.

Professional installation becomes essential in the equation. A licensed plumbing contractor not only aids in the proper sizing but also in the optimal setup and ensures that your home's hot water supply runs smoothly. Moreover, a professional will consider factors that may not be immediately apparent, such as pipe sizing, gas lines, venting, and local building codes.

In summary, navigating the large household tankless water heater sizing is a critical step toward achieving hot water harmony at home. With the correct size and professional assistance, families in larger homes can enjoy the continuous flow and convenience of a tankless system tailored to their high demand needs.

Making Sense of Tankless Water Heater Calculator Outputs

When we use a tankless water heater calculator, we're presented with data that’s crucial for making an informed decision. To interpret tankless water heater calculator results effectively, it's essential to understand what this data represents and how it aligns with our needs. The outputs we receive, such as the required temperature rise and the minimum flow rate necessary, can seem like mere numbers, but they bear significant implications on the operational efficiency of our tankless water heaters.

Our objective is to cross-reference these outputs with the specifications of available tankless water heater models. This ensures we hone in on a unit that can deliver the performance we require without falling short or exceeding our requirements to the point of redundancy. A closer look at the calculator results allows us to understand water heater calculator results in the context of our household’s daily usage and peak periods.

Decoding the Temperature Rise and Flow Rate Data

The temperature rise, indicated by the calculator, reflects the difference between our input water temperature during the coldest days and our desired output temperature. This is pivotal because an incorrectly estimated temperature rise can lead to consistently insufficient hot water or, conversely, an overworked heating unit. Similarly, the minimum flow rate is indicative of the quantity of hot water needed at any given time when various fixtures are in use simultaneously. It is a measurement that assures us that during peak usage times, we won't be left wanting.

Based on the complexities of these figures, we’ve created a sample table that aligns potential calculator outputs with the corresponding water heater model specifications:

Calculated Output Model Specification Application Suitability 5 GPM with 70°F Rise Model A: 6 GPM at 75°F Rise Highly Suitable for Large Homes 3 GPM with 60°F Rise Model B: 3 GPM at 70°F Rise Suitable for Small to Medium Homes 7 GPM with 65°F Rise Model C: 8 GPM at

Lightning fast quotes.

Our water heater experts are standing by to help. Complete our form or call to schedule service.

Get a quoteA picture of a water heaters now technician.