How Much Propane Does a Tankless Water Heater Use?

A tankless water heater is a type of water heater that does not store hot water in a tank. Instead, it draws from a natural gas or propane line and heats the water when needed. A traditional storage-tank water heater stores several gallons of hot water at any given time, and it produces hot water by heating this accumulated liquid until it reaches your desired temperature. But exactly how much propane does a tankless water heater use?

How Much Propane Does A Tankless Water Heater Use?

Tankless water heaters work efficiently more than traditional water heaters. This is because they don’t have to keep large amounts of hot water available at all times to use far less propane.

However, the amount of propane used by your tankless water heater is dependent on several factors. For instance, the capacity of your tankless water heater and how long you use it in one go will significantly affect the amount of propane consumed. 

By design, tankless water heaters use less propane than traditional water heaters. The average tankless water heater uses about 1/3 less propane than a conventional tank water heater. However, the exact amount of propane used by your water heater will vary.

Factors that Influences the Rate of Propane Consumption by Tankless Water Heater

Many factors influence the rate at which your tankless heater uses propane. The most important ones are:

The efficiency of your tankless heater

The manufacturer determines the efficiency of your tankless heater. But it can be affected by other factors, such as how often you use the water heater and how much heat transfer area you have. Your tankless water heating system may only be as efficient if you use it regularly (for example, when work or travel takes you away from home for long periods).

The efficiency of your tankless water heater influences how much energy it uses to heat the water. If a unit has a good rating, you can expect to use less energy than one with a poor rating. You should know your unit’s energy efficiency level (EER) before purchasing it.

Also, some models have dual-fuel systems, so they can run on electricity or propane. These tend to use less propane than single-fuel models because they don’t need all their power from gas.

Quality of the installation to match your space

You’ll also want to ensure that your installation is done well, as a poorly installed unit can cause problems. If you need to know what you’re doing or it’s simply not within your skill set, consider hiring a professional to do it for you. They will be able to advise on the best type of tankless water heater for your needs and can guide you through the process seamlessly.

It’s also worth considering whether or not there are any obstacles in the way between where the unit is positioned and where people will be using hot water from it. This distance may mean that installing a more significant capacity tankless water heater would be more efficient than installing multiple smaller ones. However, consider also that having various smaller units works out cheaper overall due to their lower upfront costs.

Usage duration

Another factor that is important in the amount of propane used by your tankless water heater is the time the heater has to work for each use. The longer you use your tankless water heater, the more propane it needs to burn. This is because the heater needs to constantly heat water flowing through it. So long as cold water is flowing, you will continue to expend propane.

The usage duration is often the most significant factor since different home activities require different propane levels. Also, suppose you run multiple fixtures simultaneously. In that case, the water heater will burn through more fuel than when running one or two faucets at once.

Ultimately, if you only use hot water for showers every few days rather than every day like most people do. In that case, this could make a difference in terms of overall consumption.

Usage frequency

Propane consumption depends on the frequency of usage and the number of people using the water heater. The bigger your family is, the higher your propane consumption can be. Different household members will perform the same task differently. This contributes massively to the total amount of propane usage. A small family of two will use around 15 gallons every month, while a family of 5-6 members will use about 40 to 50 gallons each month.

In-flow water temperature

The temperature of the water flowing into your heater is a key factor in determining how much propane your tankless water heater will consume. If you live in a cold region, it will take too much time for your water to warm up. Hence, you will need more propane for indoor water use.

The lower the temperature of water getting to your heater, the higher the amount of propane needed to heat it. For instance, if the water temperature in your area is 52o Fahrenheit, then your water heater should be able to heat it well over that temperature to attain well-heated domestic water.

How to Calculate Propane Usage for Tankless Water Heater?

You can calculate your propane usage by dividing the heater capacity of your tankless water heater by the energy content of 1 gallon of propane. The energy content of 1 gallon of propane is equal to 91,452 BTU. That means that burning a gallon of propane produces 91,452 BTU (at 100% efficiency).

This will give you the amount of propane you consume per hour at full capacity. You can also calculate how much running such a propane heater costs per hour simply by multiplying the propane usage and propane cost per gallon. However, keep in mind that propane doesn’t burn at 100% efficiency. Its burning efficiency depends on the individual heater’s EF (Efficiency Factor).


When it comes to the amount of propane used by your tankless water heater, you already know the factors in play. And although you might prepare to deal accurately with each, you often can’t always control the amount burned through. However, knowing how much propane each hot water-related activity uses can help you make an informed decision regarding budgeting. Regardless, a propane tankless water heater still uses less propane than a tank water heater since you don’t need to heat water continually. 


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