What Size Tankless Water Heater Do I Need?

If you’re asking yourself the question “what size tankless water heater do I need?”, then you’re likely going to want to take a look at this quick guide on tankless water heater sizes. There are numerous sizes to choose from, and each is designed for a certain amount of demand. Follow along for the quick rundown.

The Determining Variables

In order to properly calculate the size of the tankless water heaters the pros will install in various structures, a handful of variables are utilized. One of these variables is the demand rate, also known as “flow rate.” The flow rate is a measure of how much hot water may be needed at any given time throughout the whole of the structure.

Next, the “temperature rise” figure is established. Temperature rise is a measure of the difference between the temperature of the incoming cold water and the temperature you will ultimately want your heated water to come out at. This figure depends greatly on the region you live in, with different areas producing different water temperatures out of the ground.

Finally, structure size and the number of occupants it typically holds are also figured into the equation. For example, tankless water heaters in large houses with many occupants will typically need to be of a larger size and heating capacity in order to fulfill all of the need in addition to accommodating for heat loss through long stretches of pipe.

What Are the Options?

It’s important to get the size right when choosing a tankless water heater. This is why it’s ultimately best to let the pros handle this calculation. Too small, and you’ll get hit with ice-cold water when you least want it, while too large means for unnecessarily inflated expenses at purchase time as well as via energy consumption throughout the water heater’s time in service.

While these figures can fluctuate with various buildings and their individual needs, the following are rough estimates of what is generally acceptable in terms of tankless water heater sizes in different situations.

1-2 Household Occupants + Low to Regular Usage = 30-Gallon Model
1-2 Household Occupants + High Usage = 40-50-Gallon Model

2-3 Household Occupants + Low to Regular Usage = 40-Gallon Model
2-3 Household Occupants + High Usage = 40-50-Gallon Model

3-4 Household Occupants + Low to Regular Usage = 40-50-Gallon Model
3-4 Household Occupants + High Usage = 50-75-Gallon Model

5+ Household Occupants + Low to Regular Usage = 50-Gallon Model
5+ Household Occupants + High Usage = 75-Gallon Model

Size and Longevity

Since tankless water heaters hit the market, there has been a bit of a misunderstanding about their longevity being related to size. This is not the case. Longevity in tankless water heaters involves fuel type, brand quality, and the attributes of the water going into the water heater. Size has no relation to longevity in tankless water heaters.

If you’re asking yourself “what size tankless water heater do I need?”, it’s probably best to let the pros come take a look at your particular situation. Here at The Original Plumber, we specialize in tankless water heaters, traditional water heaters, and all other components to new and even not-so-new plumbing systems. Open seven days a week and ready for any needs you may have, we are your number-one Atlanta-area plumber.