What Size Tankless Water Heater Do I Need Calculator

Tankless h2o heaters are rated by the maximum temperature ascension possible at a given flow rate. Therefore, to size a demand water heater, you need to determine the flow rate and the temperature rising you'll need for its application (whole house or a remote awarding, such as simply a bathroom) in your home. It is important to annotation that you should never attempt and salve money by undersizing your tankless water heater.

Pace 1:

Determine the maximum number of devices yous want to run and their total flow rate. And so, add up their flow rates (gallons per infinitesimal). This is the desired flow charge per unit you'll want for the demand water heater.

For example, let'south say you look to simultaneously run a hot water faucet with a flow rate of 0.75 gallons per minute and a shower head with a flow rate of ii.6 gallons per infinitesimal. The menses rate through the demand water heater would need to be at to the lowest degree 3.26 gallons per minute. To reduce menses rates, install low-menstruation water fixtures.

Step 2:

Determine required temperature rise. To decide temperature ascent, decrease the incoming h2o temperature from the desired output temperature. Unless you know otherwise, assume that the incoming h2o temperature is l°F (By using a depression temperature assumption you ensure that you will not undersize your tankless unit of measurement.

If you alive in a warm climate your h2o temperature will likely exist much college.) For most uses, you'll want your water heated to effectually 105–115°. In this example, you'd demand a need water heater that produces a temperature rise of 55°.

Pace 3:

Sizing Example: An average shower will exist between 104–106° and uses 2.6 gallons of water. Assuming your water temperature is 40° coming into your habitation, and y'all want to produce plenty hot h2o to run 2 showers at the same fourth dimension, what temperature rise would you need to produce to achieve this?

Answer: You'll need to raise the incoming water temperature from 40 degrees to 105. Yous'll need to exist able to rut at to the lowest degree 5.2 gallons of water. So you'll need a tankless water heater that can produce at least a 60 caste ascent in temperature at 5.2 gallons per minute.

Menstruum Rates

How much hot water exercise yous need at once? Do you need to run 2 showers at the aforementioned fourth dimension or maybe a shower and a couple sinks? The chart below shows the range of h2o usage range and average water temperatures for diverse fixtures. We advise using 2.5 gpm for a shower and 1.0 gpm for a bathroom equally a reference betoken in determining your total simultaneous water needs.

Fixture	Average Menstruation GPM	Average Temp.
Tub	4.0 GPM	102°F
Shower	2.five – 3.0 GPM	104°F
Washing Machine	2.0 GPM	120°F
Dishwasher	1.5 GPM	110°F
Kitchen Sink	1.5 GPM	110°F

For case, if you are running two showers at the aforementioned fourth dimension, you will need five gallons of hot h2o per minute from the tankless water heater. If you were running a shower and the washing auto at the same time, you would need four.5 gallons per infinitesimal from the water heater. In either of these situations, you will want to size the unit that meets or exceeds how much hot water you need at the same time.

Note: tankless water heaters are intended to heat potable (drinking) water only and the inlet water to a tankless unit should not be pre-heated.

Other Sizing Notes

Gas tankless h2o heaters are able to produce a larger temperature rise per gpm than electrical models. Most need water heaters are rated for a variety of inlet temperatures. Typically, a lxx°F h2o temperature rise is possible at a flow rate of 5 gallons per infinitesimal through gas-fired demand water heaters and 2 gallons per minute through electric h2o heaters. Faster menstruation rates or cooler inlet temperatures tin can sometimes reduce the h2o temperature at the well-nigh distant faucet.

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Plagued by a chronic case of curiosity, Jeff Flowers is just a dude that annoys anybody around him with his loquacious goofiness. From beer to abode living, Jeff is just trying to hack his way through life and write a few notes nearly information technology along the way. You can follow his ramblings here, or listen to him complain nigh Austin traffic on Twitter at @Bukowsky.

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