What if you could ensure that you'd never run out of hot water again during a shower while simultaneously saving energy on your monthly utility bills? Tankless water heaters, known as on-demand water heaters, are easiest and most cost-effective ways to lower your energy bills quickly. The more conventional tank-style heaters utilize an enormous amount of energy to heat anywhere between 40 to 120 gallons of water around the clock, even when no one is in the home. Water heater timers can help you cut back on the energy associated with hot showers. The US Department of Energy reports that 17 percent of total household energy usage is consumed by water heating. In most homes, that's more than all other household appliances combined.
Below, we offer a complete guide to how you can switch to tankless water heaters to save energy and money.
The majority of homeowners continue to rely on large, bulky, inefficient tank-style water heaters for their homes. As we mentioned in the introduction, the main drawback to these types of water heaters is that they require an enormous amount of energy to keep water hot 24 hours a day. While you're at work or school or on a two-week vacation, your water heater will continue to either use gas or electricity to heat that water.
What is a Tankless Water Heater?
Tankless water heaters heat water on demand, without relying on any storage tank. When someone in the household turns on the hot water tap, the cold water will travel through the heater where the water is instantaneously heated. There are both electric and gas tankless water heaters available.
There are essentially two different ways to set up a tankless water heater in your home: a more extensive, centralized heater that delivers hot water to the entire home or point of use (POU) heaters, located near the faucets, showerheads, or appliances to which they will be explicitly delivering hot water.
What Is a Gas Powered Tankless Water Heater?
With on-demand gas water heaters, a small gas burner can run off propane or natural gas. One of the main pros of gas on-demand water heaters is that it generally allows for higher flow rates, in some cases up to 5 gallons per minute (GPM). This amount will give you more than enough hot water flow to run several faucets or appliances at once.
The main drawback of using gas is that your home will continue to rely on fossil fuel sources of energy instead of transitioning into an all-electric home powered entirely by renewable sources of energy. In addition, gas-powered on-demand water heaters require ventilation outside the house, thus increasing installation costs. However, Rise estimates that a gas-powered water heater could save your family around $100 each year, allowing for a payback period between 2 and 6 years.
What Is an Electric Tankless Water Heater?
A tankless electric water heater utilizes a powerful electric heating element that instantaneously heats water as it passes through the unit. Homeowners can expect this type of on-demand heater to deliver an average savings of $100 per year. Though these types of tankless water heaters do not require any ventilation, the powerful heating element might need some homeowners to upgrade their home's electrical panel.
What Are the Different Types of Tankless Water Heaters?
There are essentially two different ways to set up a tankless water heater in your home: a more extensive, centralized heater that delivers hot water to the entire home or point of use (POU) heaters, located near the faucets, showerheads, or appliances to which they will be explicitly delivering hot water.
What Is a Whole-Home Tankless Water Heater?
The advantage of more extensive and centralized on-demand water heaters is that they generally require less plumbing and electrical or gas connections. This feature results in lower installation costs. A centralized on-demand water heater is still significantly smaller than a tank-style heater. It can be discretely located in several locations around the home. One of the cons of tankless electric heaters is that the device might not provide enough hot water for multiple, simultaneous uses if they are undersized. For example, if you are showering and running the dishwasher simultaneously, the heat load may be too much for the water heater. The result will be lukewarm (instead of hot) water delivery to both appliances.
What Is a Point of Use Tankless Water Heater?
Point of use tankless water heaters is generally much smaller than centralized versions. They are made to be small, to fit in tiny places, like cupboards underneath your sink or in the bathroom closet near your showerhead. The Energy Star Program states: "Adding a POU at the fixture may be the best option in terms of system-wide energy efficiency, especially compared to the alternative of increasing the temperature setting of a storage water heater."
Point of use, tankless water heaters are generally a good option for households with relatively low hot water requirements (20-25 gallons per day). The main disadvantage is that you'll have to install several tankless heaters wherever you want hot water available. A 3,500 square foot home with five bathrooms, then, would probably not be an ideal candidate for POU heaters.
However, POU on-demand water heating can allow homeowners greater control over where hot water is directed. For example, though hot showers are indeed a luxury that most of us have come to depend on, do we need a hot water plumbing fixture attached to our washing machine? Between 80 and 90 percent of the energy used by a washing machine is used for heating water. By simply omitting a hot water connection (and only using the cold setting on our washers), we can radically reduce power consumption during laundry day.
What Size Tankless Water Heater do I Need?
The size of a tankless water heater refers to both the temperature rise and the flow rate. The temperature rise is how hot the device can heat water. The flow rate refers to the number of gallons of water effectively heated and distributed to the home.
If you decide to opt for point-of-use heaters, most of these smaller options come in predetermined sizes and flow rates. For example, a typical POU heater will have a temperature rise between 65 and 75 degrees Fahrenheit and a flow rate of between 1 and 5 GPM. Smaller, under-the-sink types of POU heaters that only heat water for faucets might have lower flow rates of 0.5 GPM.
To properly size the water heater for POU uses, consider your faucet or showerhead's flow rate. Low-flow showerheads generally have a flow rate of about 2.5 GPM, so you'll need an option that has a flow rate at least equal to that. For centralized tankless water heaters, the average flow rate is usually between 4 and 8 GPM. Gas-powered on-demand heaters generally allow for a higher flow rate than their electric counterparts.
To correctly determine the optimum size of your tankless water heater, you'll need to ask yourself the following:
- Determine the maximum number of faucets, showerheads, appliances that you want to run through the on-demand heater and their total flow rate measured in gallons per minute.
- Add up the above. This sum will give you the flow rate you'll need for your on-demand water heater. Keep in mind - you will rarely use all of the devices at once, but to be on the safe side, assume that they are all running to avoid under-sizing your unit.
- Next, determine your required temperature rise. To do this, you'll need to measure the temperature of water incoming through your faucets (a simple thermometer will work) and subtract that from the desired output temperature. For reference, the average shower temperature is 105 degrees Fahrenheit. The resulting number will be the needed temperature rise.
Size matters when it comes to your tankless water heater. In fact, it is the most important part of choosing a new unit for your home.
Example Tankless Water Heater Size Assessment
Let's say you need a tankless water heater to power two showers and two sinks.
- You have low-flow showerheads that use 1.8 GPM and faucet aerators with flow rates of 1.2 GPM, so you need a maximum flow rate of 6 GPM.
- Your incoming water temperature is 40 degrees Fahrenheit, and you want an average shower temperature of 105 degrees. So it would be best if you chose an option with an advertised temperature rise of at least 65 degrees.
How to Install a Tankless Water Heater
Unless you have serious DIY construction abilities, you will most likely want to hire a professional for installation. On-demand gas heaters will require the installation of vents. Electric heaters will require electrical connections that you'll not want to fool around with unless you have some electrical knowledge. In addition, there can be several building elements, such as mandatory gas shut-off valves, that professional installers will know about and how to install correctly. If you have the skills and choose to self-install your tankless water heater, the following YouTube instructional video is an excellent place to start.
What Are the Downsides of a Tankless Water Heater?
With so many economic and energy efficiency benefits, why isn't everyone installing tankless water heaters? The main downside is that for larger homes with several bathrooms, even the largest on-demand heater might not be able to simultaneously deliver hot water to all your plumbing connections at once. For example, if a family of six all takes showers in their private bathrooms simultaneously, this could lead to only lukewarm shower temperatures.
Having a water heater that is too small will result in it not being able to produce enough hot water for your household demand. For example, you might not be able to run more than one shower at a time without someone getting an arctic blast of cold water.
On the other hand, a water heater that is too large will end up being more costly than necessary, since you will be paying more upfront for the larger size (although it could be useful if you plan to upsize your home later).
To work properly, a tankless water heater needs to be just the right size to meet your home's hot water demand. This guide will teach you how to size a tankless water heater and includes a calculator at the end.
Tankless Sizing Overview
There are two factors that need to be considered when sizing a tankless water heater:
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Flow Rate (GPM): How much hot water you will need at any given time
- Temperature Rise (ΔT): The difference between the incoming cold water temperature and the desired temperature
First, figure out which fixtures you will want to operate simultaneously and how much hot water each will use.
This is called the flow rate and is measured in gallons per minute (GPM). You can determine the total rate at which the water heater will need to produce hot water by adding the flow rates for each fixture together.
Next, calculate the temperature difference between the water entering the heater (groundwater temperature) and the temperature desired at the faucets. This is called your temperature rise (known as ΔT by professionals), or the temperature by which your water heater must raise the water.
Typical faucet temperatures are 110° F – 120° F. Groundwater temperatures average 57° F in the U.S. but can range from approximately 70° F in southern parts of Florida, to near freezing in the northern states.
The greater the difference between the groundwater and desired fixture water, the fewer fixtures a water heater will be able to supply.
Tankless Sizing Calculator
Use the two tables below to calculate the total flow rate your home needs. Be sure to only include the maximum number of fixtures you will want to operate simultaneously in the calculation table.
1. Figure out the flow rate for the heaviest water use you expect.
For example, let's say you're running one standard shower, a dishwasher, a faucet, and a high-efficiency washing machine at the same time. Using the water flow rate table below, add up all the flow rates of those fixture (2 + 2.5 + 1 + 1 = 6.5GPM). Your flow rate would be 6.5GPM.
2. Use the groundwater temperature map to locate your groundwater temperature based on where you live in the United States.
110 Voltage : In our LA CA example, entering 63 ° F yields a required temperature rise of 47 ° F.
In our LA CA example, entering 63 ° F yields a required temperature rise of 177 ° F.
4. Simply locate the appropriate water heater sizes using your information. Once you have your total flow rate and the required temperature rise, you can find the right-size tankless water heater for your home. Use the table below to navigate to the tankless water heaters that meet your GPM needs. Simply click on the appropriate GPM, and you'll be navigated to the water heaters that meet those needs.
In our example above of 6.5 GPM at 63 ° F, you would click on 6 - 8 GPM at a 60° F temperature rise in the table. (Technically speaking, you could round up to the 70° F temperature rise option, but rounding down to 60° F is the more realistic and acceptable option in this scenario since we're only 3° F under the actual rise)
