What Size Water Heater Do I need?

Are you planning to get a new water heater for your home? Confused about which one to get or what size you need? These are some questions that are likely to mess up your mind. But how about we help you with the guides for getting the ideal size for your water heater?

Size is one of the most essential factors when it comes to getting a perfect water heater. There are many sub-factors that can help you get the ideal one. If you want to know everything, then you will need to go through the whole write that will answer this most common question- what size water heater do I need?

Key Factors

If you want to look for an ideal water heater, just like we have mentioned, there are some key factors that you must keep in mind

Area Size

You will also have to ensure that you get a heater in such a size that can fit the designated space in your house.


Will you and your partner be using the heater or do you have a big family using the device? The size and occupancy of your family are also two of the most essential factors that you must keep in mind before making a purchase.

Source of Fuel

Determine the type of source of fuel. It can be electricity, natural gas or liquid propane. Besides, it can also be the one coming connected to your boiler. Once you decide this, it will help narrow your preferences down so you can have the perfect water heater for yourself.

However, suppose you have a big family in your house. In that case, you might require a high-capacity water heater so it can provide accommodations for multiple people to shower, wash dishes or do laundry at the same time. It’s because a condo will let you use the heated water for one task at a time.

Sizing of Storage Tank Water Heater

If you want to get the ideal size of a storage-tank water heater for your house, then you will need to note down the member size at first. This type of water heater sized on the basis of British Thermal Unit (BTU) input and gallon capacity. The more you will depend on hot water regularly, the more BTU inputs and gallons you will need.

This is a rough guide you can follow to get an ideal storage water heater:

Family SizeCapacity in gallons
1 to 230-gallon
2 to 340-gallon
3 to 550-gallon (electric), 40-gallon (liquid propane or natural gas)
Above 580-gallon (electric), 50-gallon (liquid propane or natural gas)

Sizing of Tankless Water Heater

A tankless water heater is rated by the highest temperature rise at a certain flow rate(gallon capacity per minute). So, to get an ideal size of a tankless water heater, you are required to determine the temperature rise and flow rate you will need for the application. The application will be varied in the size of the house. It could be within a small area such as a bathroom or could be the whole house.

Flow Rate

Firstly, you will need to list the number of hot water devices you want to use simultaneously. Afterward, add up the flow rate of the devices. The number that will come is the desired flow rate you will want for such type of water heater. Let’s say, it is likely to run a hot water tap simultaneously with a 0.57-gallon (or 2.16 liters) flow rate per minute and a showerhead with a 2.5-gallon flow rate (or 9.5 liters) per minute.

The rate of flow through the tankless water heater is required to be at least 3.25 gallons (or 12.3 liters) per minute.

Temperature Rise

Then you will need to settle on the temperature rise. For this, you will need to subtract the temperature of water incoming from the preferred output temperature. Suppose, the temperature of the incoming water is 50 degrees Fahrenheit. For most uses, you will want the water to have a temperature of 120 degrees Fahrenheit. Here, you might demand a tankless water heater that can generate a temperature rise of about 70-degree Fahrenheit

The majority of tankless water heaters are measured for a different range of inlet temperatures. In general, a 70-degree Fahrenheit temperature rise of water occurs at a flow rate of 2-gallon per minute by electric tank-less heaters and 5-gallon per minute through gas-fired ones.

Cooler inlet temperatures or faster flow rates can decrease the temperature of water sometimes at the most distant tap. There are some kinds of tank-less heaters that can be controlled thermostatically: such can differ the out temperature in accordance with the inlet temperatures and flow rates.

Sizing of Solar Water Heater

Solar water heater sizing usually involves the determination of the total collector area and the storage volume. Solar system contractor uses computer programs and worksheet so it can help in determining the system necessities and sizing of the collector.

Collector Area

The contractor basically follows a parameter of about 20 square feet of collector area for the two people mostly. For each extra person, 12 to 14 square feet is added if you dwell in the northern United States or 8 square feet is added only if you dwell somewhere in the Sun Belt area of the US.

Storage Volume

The water tank that comes with around 50 to 60-gallon capacity should be enough for two to three members. If the family is medium-sized, then a water tank of around 80-gallon capacity will be sufficient for four to five-member. If the family size is bigger than this, then a large tank will work well for around six people at the max.

The size of the solar storage reservoir rises with the collector size. In general, it will be 1.5 gallons per square foot of the area of a collector.

It will help avoid the system from getting overheated when the demand for using heated water is lower.

It’s like you will definitely not prefer using hot water in the warm sunny season right?