How would you like $15 Off a service call? Claim Yours Today.

What Size Tankless Water Heater Do I Need?

What Size Tankless Water Heater Do I Need?

correct size of tankless water heater

Perhaps the most enjoyed benefit of modern indoor living, and the most taken for granted, is a boundless supply of fresh, hot water on demand. You may not realize it, but only a few generations ago, this was an unheard of luxury in over 90% of homes. Water was pumped and heated on the stove for bathing in winter, and cold baths were the norm all summer long. 

Modern conveniences have certainly come a long way, and today, you simply turn a faucet handle and in a few seconds at most, there is clear, hot water for a variety of uses. Who doesn’t enjoy a hot shower at the end of a long, hard day or after a period of sweaty, back-breaking work? Who hasn’t basked in a long, hot soak in the bathtub for pampering and relaxation? 

pph 36 2 - What Size Tankless Water Heater Do I Need?

The unsung hero of plumbing fixtures you have to thank for this luxury is your hot water heater. There are various types and sizes to meet the different needs of modern Wisconsin homes, but perhaps one that is experiencing the most growth in popularity is the tankless water heater

If you are facing a water heater replacement or are choosing plumbing fixtures for a new home construction project, you may want to seriously consider a tankless water heater installation. Why not learn more about these versatile and energy-saving options for enjoying plenty of hot water in your home? 

What is a Tankless Water Heater? 

pph 35 1 - What Size Tankless Water Heater Do I Need?

Tankless water heaters, sometimes called “on-demand” or “instantaneous” water heaters, provide hot water only at the time it is needed and without using a storage tank. By not keeping a supply of water heated in a large tank, less energy is used and you save money. But a correctly-sized tankless water heater installation can provide more than enough hot water for your family’s needs. 

A tankless water heater heats water directly as it passes through the unit and then sends the heated water on to your sink, shower, or appliance. No water is stored in a holding tank, as with the more traditional tank water heater. Cold water enters the heating unit when a hot water tap is turned on, and is heated with either electricity or a gas burner. 

Because these units do not utilize a large storage tank, they are considerably smaller than traditional hot water heaters and therefore occupy less space. In fact, there is often plenty of room for installing more than one tankless water heater for different uses. Some larger families with greater needs for hot water may want to consider this option.  

Considering the Right Tankless Water Heater Installation

pph 34 - What Size Tankless Water Heater Do I Need?

The average tankless water heater is able to supply a steady stream of hot water at a rate of 2–5 gallons (or 7.6–15.2 liters) per minute. Gas-fired tankless water heaters typically generate higher flow rates than electric models. Depending on your family’s usage habits, even the largest, most efficient model of tankless water heater may not supply an adequate amount of hot water. 

For example, if you routinely have a family member taking a shower while someone else is running the dishwasher, this can stretch your tankless unit to its limit, or even beyond. Larger households that require simultaneous showers or other multiple uses of hot water may require separate tankless water heater installations to handle the load. 

With this type of system, one tankless water heater may be used to supply only appliances, such as the clothes washer and dishwasher, while another separate unit supplies the sinks and showers. Other special applications that will likely demand multiple tankless water heaters include: 

Calculating Your Needs Before a Tankless Water Heater Installation 

pph 33 - What Size Tankless Water Heater Do I Need?

Choosing the correct size of tankless water heater for your home’s needs is critically important. As we have seen, a unit that is too small cannot produce enough hot water, leaving your family frustrated and unhappy. Conversely, a unit that is too large can waste energy and cost more to operate than necessary — and no one likes to waste money.  

Two factors guide how you can choose the correct tankless water heater for your home: 

  • Flow Rate (GPM) – This is how much hot water you will need at any given time.
  • Temperature Rise (ΔT) – This is the difference between the temperature of the incoming water and your desired hot water temperature. 

Calculating Flow Rate

In order to calculate flow rate, you will need to identify the fixtures you are likely to operate simultaneously and determine how much hot water each fixture will use. Then, you must combine these amounts to generate the total flow rate necessary for your tankless water heater in gallons per minute.

How much hot water will you need at one time? Will it be necessary to operate two showers at the same time, or maybe one shower and up to two sinks? These are some of the basic questions you must ask to begin calculating the size of tankless water heater you need. 

pph 32 - What Size Tankless Water Heater Do I Need?

Below are some average water usage rates for various fixtures. It is likely prudent to estimate about 2.5 gpm for a shower and 1.0 gpm for a bathroom when determining your total simultaneous water requirements. 

Fixture/Appliance Average Water Flow in GPM 

  • Kitchen Sink 1.5 
  • Dishwasher 1.5
  • Bathroom Sink 1.5
  • Bathtub 4
  • Shower 2.5 – 3
  • Washing Machine 2

So, for example, if you wish to operate a dishwasher and at least one shower at the same time, your tankless water heater will need to produce at least 4 GPM of hot water. Other variations could include: 

  1. Two showers and two sinks: 8 GPM
  2. One sink and the washing machine: 3.5 GPM 
  3. One shower and the washing machine: 4.5 GPM 

Calculating Temperature Difference 

Now, you must calculate the change in temperature necessary from the incoming water supply to your desired hot water temperature at the fixtures. Professional plumbers call this your temperature rise (symbolized like this: ΔT). 

Consider that the average groundwater temperature in the United States is 57°F and the average desired temperature at the faucet for most homes is between 110°F and 120°F. Here in Wisconsin, groundwater temperatures average about 50°F. 

This is important information because a greater difference between the groundwater temperature and your desired hot water temperature means your tankless water heater will be able to supply fewer fixtures or appliances simultaneously. 

Figuring the Size of Tankless Water Heater You Need 

For example, your home’s shower uses 2.5 GPM and you want the water temperature to be about 104–106°F. If the water temperature is at 50° coming into your home, your tankless water heater will need to be capable of producing a 54 degree rise in temperature at 2.5 gallons per minute. But remember, this is only for the shower. If you plan to run two or more fixtures or appliances simultaneously, they must also be factored into the equation. 

Figure out the likely combination of appliances and fixtures you will use simultaneously on a routine basis and add the total gallons per minute. This will help you determine the size of the unit you will need to meet your hot water demands, or if a multiple tankless water heater installation is warranted. Remember, you want the size or combination of units that will meet or slightly exceed your hot water needs when figuring the most likely usage at one time. 

Advantages of a Tankless Water Heater Installation 

pph 31 1 - What Size Tankless Water Heater Do I Need?

If your Wisconsin home consumes an average of 40 gallons or less of hot water each day, the right size of tankless water heater can save you between 24% and 34% on your energy costs over traditional tank storage water heaters. For homes that consume more hot water, larger families that use around 80 gallons per day, the savings can still be between 10% and 15%. In some multiple unit installations, you could achieve a savings of between 30% to 50%.  

A tankless water heater installation will cost more initially, over a conventional storage tank water heater. But a tankless water heater will last longer, need less maintenance, and have lower operating costs than conventional water heater units. This will offset the higher purchase price in almost every case, especially when you consider that most tankless water heaters will last over 20 years. Compare that to the typical storage tank water heater that lasts an average of 10–15 years.

Professional Tankless Water Heater Replacement & Installation 

If you’re wondering how to install a tankless water heater, and if you can do it yourself, we recommend erring on the side of caution. As with any water heater installation, some electrical wiring and plumbing will be required, chores that are typically best left to professionals. If your tankless water heater uses gas to heat water, there are the additional risks with plumbing gas lines. Not to mention acquiring the necessary permits and inspections to ensure safety.  

pph 30 - What Size Tankless Water Heater Do I Need?

You need trained, experienced, and reliable plumbing professionals who can handle all the wiring, gas lines, and plumbing tasks associated with a tankless water heater installation. Plymouth Plumbing & Heating serves all of eastern Wisconsin with licensed, knowledgeable, and experienced repair and installation services, including tankless water heater installation. We can help you select the proper size and configuration as well as install the complete system. 

And remember, you can call Plymouth Plumbing & Heating for professional repair service 24 hours a day, 7 days a week, 365 days a year. Call us now to ask for assistance or to inquire about a tankless water heater installation. 

Get a Free Estimate

At Plymouth Plumbing and Heating, we guarantee the highest quality work at the best prices around. It cost's you nothing to get a Free Estimate from our team of experts today.

Request Free Estimate