Are you currently considering replacing your existing water unit with a 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 size options with different gallon capacity out there.

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

Table of Contents

## 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 finding 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 an accurate answer, you need to estimate the amount of hot water used by the household during the “peak” hour. 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. Suppose you wonder what size water heater for a 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 heaters has a first-hour rating that refers to how many gallons of water it’s capable of delivering in the first one hour in full condition.

## How Big of a Tankless Water Heater Do I Need?

Tankless water heaters 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 the water heater.

Calculate the desired temperature increase by subtracting the input temperature from the 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 an area with a warmer climate.

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

The water temperature needs to be increased from 40°F to 105°F, and you need to heat 6 (3×2) gallons of water. Therefore, you want a tankless water heater that can generate a minimum of 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 can maintain low temperatures. In general, you’ll need the only 120°F of heat at maximum. A well-insulated house won’t need more than 15 Btu/sq ft/hour. So, if you have a 2,000 sq ft house, you need about 30,000 Btu/hour water heater.

So, have you determined the answer to “how big of a water heater do I need” question yet? As most households 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 the tank or not.