How Big of a Water Heater Do I Need? Here’s A Simple Guide

Are you currently considering replacing your existing water unit with water heater? With tank or not, it can be confusing to determine the right size of water heater that will cater to your household needs – there are so many tank sizes options with different gallon capacity out there.

How Big of a Water Heater Do I Need

The explanation below may be able to help you find your question of how big of a water heater do I need in easy-to-understand way.

How Big of a Water Heater Do I Need?

The more members in your household, the more your water usage will be. The key to find the right water heater size, in fact, relies on the numbers of its users. Your household size is a primary indicator to determine your hot water tank size.

To come with accurate answer, you need to estimate the amount of hot water that will be used by the household during the “peak” hour as well. However, it can also be roughly estimated from the numbers of your family members alone, which would be:

  • 1 – 2 people: 30 to 40 gallons
  • 2 – 3 people: 40 to 50 gallons
  • 3 – 4 people: 50 to 60 gallons
  • More than 5 people: 60 to 80 gallons

So, take an example, if you wonder what size hot water heater for family of 4, generally any tank between 50 gallons to 60 gallons would suffice. Remember that the chart above is an extremely general guideline that yet to factor the busiest hour your family uses the water heater on – because each of the tank-style water heater has first-hour rating that refers to how many gallons of water it’s capable to deliver in the first one hour in full condition.

How Big of a Tankless Water Heater Do I Need?

Tankless water heater are categorized by the highest possible temperature increase in any flow rate. Thus, to determine your needed size, you have to estimate the required flow rate and temperature increase during use.

Calculate the maximum appliances numbers to run simultaneously and their flow rate (gallons/minute) in total. The result is the required flow rate for water heater.

how big of a tankless water heater do i need

Calculate the desired temperature increase by subtracting the input temperature from output temperature that’s desired. The general assumption of input temperature is 50°F, but the number is likely to be higher if you live in area with warmer climate.

To give you an example, in average, showers have temperature of 105°F and utilize about 3 gallons of water. Now, assuming you want the water heater to supply two showers at same time and the input temperature is 40°F, how many of temperature increase you will require?

The water temperature needs to be increased from 40°F to 105°F and you need to heat 6 (3×2) gallons of waters. Therefore, you want a tankless water heater that is able to generate minimum 60°F of temperature increase at 6 gallons/minute.

How Big of a Water Heater Do I Need for Radiant Heat?

Water heaters can be used to provide radiant floor heating, as they are able to maintain low temperature. In general, you’ll need only 120°F of heat at maximum. A house that’s well-insulated won’t need more than 15 Btu/sq ft/hour. So, if you have 2,000 sq ft house, you need about 30,000 Btu/hour water heater.

So, have you determined the answer of “how big of a water heater do I need” question yet? As most household are comprised of four family members, the 50 gallon water heater is the most common size of tank you can find – but of course, there are plenty of water heater models available, with tank or not.