Tankless water heaters are a great way to save energy and space in your home. Unlike traditional tank water heaters, tankless models only heat water as it’s needed, so there’s no need to keep a large tank of hot water constantly heated. However, one of the biggest questions people have when considering a tankless water heater is, “What size do I need?” In this article, we’ll walk you through the factors to consider when determining the size of a tankless water heater for your home.
Factor 1: Flow Rate
One of the most important factors to consider when choosing a tankless water heater is flow rate. Flow rate refers to the amount of hot water that can be delivered at a time. To determine the flow rate you need, you’ll need to consider the number of appliances and fixtures that will be using hot water at the same time.
Here are some examples of the average flow rates for common household fixtures:
- Shower: 1.5 – 2.5 gallons per minute
- Kitchen sink: 1.5 – 2.5 gallons per minute
- Bathroom sink: 0.5 – 1.5 gallons per minute
- Dishwasher: 1 – 2.5 gallons per minute
- Washing machine: 1.5 – 3 gallons per minute
Add up the flow rates of all the fixtures and appliances that will be in use at the same time to determine the total flow rate you’ll need from your tankless water heater.
Factor 2: Temperature Rise
Another factor to consider when sizing a tankless water heater is temperature rise. Temperature rise refers to the difference between the temperature of the incoming cold water and the temperature of the hot water that you want. The higher the temperature rise, the more powerful the tankless water heater needs to be to keep up with demand.
For example, if the incoming cold water temperature is 50 degrees Fahrenheit and you want your hot water to be 120 degrees Fahrenheit, the temperature rise is 70 degrees Fahrenheit.
Factor 3: Size of Household
The size of your household also plays a role in determining the size of tankless water heater you need. A larger household with more people using hot water will require a more powerful tankless water heater to keep up with demand.
Factor 4: Groundwater Temperature
Groundwater temperature varies depending on your location. The colder the groundwater temperature, the more powerful your tankless water heater will need to be to heat the water to the desired temperature.
Factor 5: Peak Demand
Peak demand refers to the maximum amount of hot water that will be used in your home at any given time. This is important to consider when sizing a tankless water heater because it determines the maximum flow rate that the heater will need to be able to handle.
Calculating the Size of Tankless Water Heater You Need
To calculate the size of tankless water heater you need, you’ll need to consider all of the factors we’ve discussed. Here’s a step-by-step guide:
Determine the flow rate needed.
Add up the flow rates of all the fixtures and appliances that will be in use at the same time to determine the total flow rate you’ll need from your tankless water heater.
Calculate the temperature rise.
Determine the difference between the temperature of the incoming cold water and the temperature of the hot water that you want. The higher the temperature rise, the more powerful the tankless water heater needs to be to keep up with demand.
Calculate the size of the tankless water heater needed.
Use the following formula to calculate the size of tankless water heater you need:
Flow rate x temperature rise = required BTUs
BTUs ÷ 120,000 = required gallons per minute (GPM)
For example, if you live in the Northeast region of the United States where the incoming water temperature is around 37-52°F, you will need a larger tankless water heater than if you live in the Southwest region where the incoming water temperature is around 57-77°F. It’s important to take these regional differences into account when determining the size of your tankless water heater.
Additionally, you may want to consult with a professional plumber or HVAC technician to ensure that you select the right size tankless water heater for your home. They can help you calculate your home’s hot water demand based on your family size, the number of bathrooms in your home, and your typical hot water usage patterns.
Consider Other Factors
In addition to hot water demand and incoming water temperature, there are other factors to consider when selecting the right size tankless water heater for your home. For example, you may want to consider the flow rate of your home’s fixtures and appliances, such as showers, dishwashers, and washing machines.
You may also want to consider whether you have low-flow fixtures or appliances that require a lower flow rate. These types of fixtures and appliances can help you conserve water and reduce your hot water demand, which may allow you to choose a smaller tankless water heater.
Conclusion
Selecting the right size tankless water heater is essential for ensuring that your home has a reliable supply of hot water. By considering your hot water demand, incoming water temperature, and other factors, you can select a tankless water heater that meets your needs and saves you money on energy costs.
If you’re not sure which size tankless water heater is right for your home, consult with a professional plumber or HVAC technician. They can help you calculate your hot water demand and select the right size tankless water heater to meet your needs.
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