Greetings readers! Today’s topic will be about sizing tankless water heaters. With the rising demand for energy-efficient and cost-effective solutions, more households are switching to tankless water heaters. However, one common mistake people make is choosing the wrong size. Don’t worry, we’ve got you covered! In this article, you’ll learn everything you need to know about how to size a tankless water heater.
Introduction
Before we dive deep into the sizing process, let’s first discuss what exactly is a tankless water heater. Unlike traditional water heaters that store hot water in a tank, tankless water heaters heat water directly as it flows through the unit. This provides an endless supply of hot water on-demand. Moreover, tankless water heaters are more energy-efficient and durable than storage tank water heaters.
However, selecting the right size is crucial to ensure optimum performance and efficiency. If the heater size is too small, it won’t provide enough hot water for your household’s needs. On the other hand, if the size is too big, you’ll be wasting energy and money.
So, how do you determine the right size? Let’s find out!
1. Determine your required flow rate
The first step to sizing a tankless water heater is calculating your household’s required flow rate. This refers to the amount of hot water your family needs at peak usage. You can determine your required flow rate by adding up the flow rates of all hot water appliances you use simultaneously. Refer to the table below for average flow rates of common household appliances.
| Appliance | Flow Rate (GPM) |
|---|---|
| Shower – low flow | 1.5 |
| Shower – high flow | 3.0 |
| Bathroom sink | 0.5-1.5 |
| Kitchen sink | 1.0-2.5 |
| Dishwasher | 1.0-3.0 |
| Washing machine | 1.5-3.0 |
For example, if you need to use the shower and the dishwasher simultaneously, your required flow rate would be 4.0 GPM (3.0 + 1.0).
2. Calculate your required temperature rise
The next step is to calculate your required temperature rise. This refers to how much the incoming water temperature needs to be raised to meet your desired hot water temperature. The ideal hot water temperature is typically between 110-120°F.
For instance, if the incoming water temperature is 50°F, and you want the hot water temperature to be 120°F, the required temperature rise would be 70°F.
3. Use the flow rate and temperature rise to determine the heater size
Now that you know your required flow rate and temperature rise, you can use these values to determine the appropriate tankless water heater size. Generally, the size is measured in gallons per minute (GPM). Most tankless water heaters have a maximum flow rate ranging from 6-10 GPM.
To calculate the required size, use this formula:
Required GPM = (Required flow rate) x (Required temperature rise) / (Temperature rise per GPM).
Temperature rise per GPM refers to how much the temperature rises per gallon of water per minute. This varies depending on the model and manufacturer of the tankless water heater. Refer to the manufacturer’s specifications to determine the temperature rise per GPM.
4. Consider other factors
Aside from your household’s required flow rate and temperature rise, there are other factors you should consider when sizing a tankless water heater. These include:
- Peak usage times
- Number of bathrooms
- Number of hot water appliances
- Cold water temperature
- Altitude
It’s important to factor in these variables to ensure that you’re choosing the right size for your household’s needs.
Advantages and Disadvantages
Advantages:
1. Energy-efficient: Tankless water heaters only heat water as it’s needed, which saves energy and reduces utility bills.
2. Space-saving: Unlike storage tank water heaters, tankless water heaters are compact and can be mounted on walls, saving valuable floor space.
3. Long-lasting: Tankless water heaters have a longer lifespan than storage tank water heaters, with an average of 20 years or more.
4. Endless hot water: Tankless water heaters provide a continuous supply of hot water on-demand, eliminating the need to wait for the tank to refill.
Disadvantages:
1. High upfront cost: Tankless water heaters are more expensive upfront than storage tank water heaters.
2. Installation costs: Tankless water heaters may require professional installation, which can add to the overall cost.
3. Limited flow rate: Tankless water heaters have a limited flow rate, which means that they may not be suitable for larger households with high hot water demand.
4. Cold water sandwich: Some tankless water heaters may experience a cold water sandwich effect, which is when there’s a brief moment of cold water before the unit heats the water to the desired temperature.
Table: Tankless Water Heater Size Chart
| Household Size | Flow Rate (GPM) | BTU/Hour |
|---|---|---|
| 1-2 people | 2.5-4.0 | 120,000-150,000 |
| 2-3 people | 3.5-5.5 | 150,000-195,000 |
| 3-4 people | 4.0-6.5 | 195,000-255,000 |
| 5 or more people | 6.5-8.0 | 255,000-300,000 |
FAQs
1. Can I install a tankless water heater myself?
No, it’s recommended to hire a professional plumber or electrician for proper installation.
2. How long do tankless water heaters last?
Most tankless water heaters have a lifespan of 20 years or more.
3. Do tankless water heaters require maintenance?
Yes, it’s recommended to have your tankless water heater serviced annually to ensure optimum performance.
4. Can I replace my storage tank water heater with a tankless water heater?
Yes, you can replace your storage tank water heater with a tankless water heater. However, you’ll need to ensure that the unit is properly sized for your household’s needs.
5. Can a tankless water heater run out of hot water?
No, tankless water heaters provide an endless supply of hot water on-demand.
6. How much does a tankless water heater cost?
The cost of a tankless water heater varies depending on the model and manufacturer. However, the average cost ranges from $500-$2,500.
7. Can a tankless water heater be used for radiant floor heating?
Yes, some tankless water heaters can be used for radiant floor heating. However, you’ll need to ensure that the unit is properly sized for your heating needs.
8. How much space does a tankless water heater require?
Tankless water heaters are compact and can be mounted on walls, saving valuable floor space.
9. What size circuit breaker do I need for a tankless water heater?
The circuit breaker size varies depending on the unit’s voltage and amperage. Refer to the manufacturer’s specifications for the recommended circuit breaker size.
10. Can a tankless water heater be used for both residential and commercial purposes?
Yes, some tankless water heaters can be used for both residential and commercial purposes. However, you’ll need to ensure that the unit is properly sized for your needs.
11. Can a tankless water heater be installed outdoors?
Yes, some tankless water heaters are designed for outdoor installation.
12. Do tankless water heaters require a vent?
Yes, tankless water heaters require a vent to remove exhaust gases.
13. Can I use a tankless water heater with hard water?
Yes, you can use a tankless water heater with hard water. However, hard water can cause a buildup of minerals that can affect the unit’s performance. It’s recommended to install a water softener to prevent mineral buildup.
Conclusion
Now that you know how to size a tankless water heater, you can make an informed decision when choosing the right size for your household’s needs. Remember to calculate your required flow rate and temperature rise, factor in other variables, and refer to the manufacturer’s specifications for the appropriate size.
Investing in a tankless water heater can provide many benefits, including energy efficiency, space-saving, and endless hot water on-demand. However, it’s important to weigh the advantages and disadvantages before making a decision.
Don’t forget to hire a professional plumber or electrician for proper installation and maintenance. A well-sized and properly installed tankless water heater can provide hot water comfort and convenience for years to come!
Closing Disclaimer
The information provided in this article is for educational purposes only and not intended to diagnose, treat, cure or prevent any disease. Consult with a professional plumber or electrician for proper installation and maintenance of your tankless water heater. We do not endorse any specific product or brand mentioned in this article.
