Sizing a tankless water heater correctly for your home is important. Inaccuracy will lead to comfort issues, low hot water pressure, reduced equipment lifespan and increased total costs. Proper sizing is complex and involves many more factors than sizing a tank water heater. This is why it’s so important to hire a professional plumber who helps you account for all dynamics. Let’s explore them.
Flow Rate
In order to size a tankless water heater, you need to determine how much flow your household needs. Factors include the size of the home and the number of residents, fixtures and appliances. The plumbing industry in the U.S. measures the flow rate in gallons per minute (GPM). The smallest systems on the market provide about 2 GPM. The largest systems provide 10 GPM or more. Each fixture in your home requires a certain flow rate. The typical faucet requires 1 GPM or less. The standard showerhead uses around 2 GPM. Standard washing machines and dishwashers will both use approximately 2.5 GPM.
High-Efficiency Fixtures and Appliances
When transitioning to a tankless water heater, it may be worthwhile to consider high-efficiency fixtures as well. Low-flow showerheads, for instance, use about 1.6 GPM. High-efficiency dishwashers and washing machines lower consumption by about 1 GPM each. Each upgrade may be small. That said, it can add up to a dramatic difference in how much flow rate you need overall.
Peak Demand
It’s important to consider flow rate within the context of peak demand. You’ll likely never need to run all the fixtures and appliances in your home at the same time. That may not even be possible based on the technologies available. What you need to determine is how much you will need and when. For a family of four that all gets ready in the morning, you’ll have to account for showers, faucets, toilets and perhaps a washing machine. The goal is to choose a flow rate that exceeds your peak demand by at least a little.
Oversizing Your Tankless Water Heater
Some homeowners choose to size their tankless water heaters not on daily peak demand but on annual peak demand. Perhaps you host family or friends for the holidays or have children home from college during the summer. One of the great advantages of a tankless water heater is that you can efficiently do this. The added flow rate will cost you more upfront, but it won’t cost you daily. This type of sizing is not practical with a traditional water heater. You’d be paying for the added capacity day in and day out.
Groundwater Temperatures
Another reason it’s important to hire a professional plumber is the temperature of your groundwater. When sizing tankless water heaters, there’s a concept called temperature rise. A tankless water heater has a limited capacity to heat water. Consider the same unit used in areas with 60- and 70-degree groundwater. In the colder area, the system would provide a lower flow rate. This is why homes in the North typically need a higher flow rate than those in the South.
Fuel-Burning vs. Electric Units
Fuel-burning tankless water heaters are typically more economical over their lifespans. There are exceptions, such as small homes with below-average daily demand for hot water. Fuel-fired tankless water heaters tend to provide a higher flow rate at the same temperature. This is because they have greater heating capacity and are better able to overcome the issue of temperature rise.
Single- vs. Multi-Unit Installations
You can install a single tankless water heater that provides hot water to your entire home. You can also purchase two or more units and break your home down into zones. This has become a common approach in larger homes. It does cost more upfront but can save you considerably over the long term. In this case, your plumber needs to determine the flow rate for each zone independently.
Would You Like to Install a Tankless Water Heater in Lubbock?
Action Air Plumbing and Septic is a family-owned and -operated business that’s served Lubbock and all of West Texas for more than 35 years. Our expert plumbers install water heaters and service tankless and tank water heaters, including performing conversions from electric to gas.
We pipe and repipe water, sewer and gas lines, too! Our team specializes in septic plumbing. You can also count on us for draining cleaning and slab leak repair. Our company has an HVAC team as well. We install, replace, repair and maintain furnaces, heat pumps, air conditioners and ductless mini-splits. If you have questions or would like to request service, call today, or contact us online.
