How Much Propane Do You Need for a Tankless Water Heater?

Tankless water heaters are a great solution to a common problem. They give you hot water for your home without the space required for a hot water tank. In this article, we’re seeing just how efficient a propane tankless water heater is. We’ll examine how much propane is used by a tankless water heater, and how you can determine the cost associated with this propane use.

How Much Propane Do You Need for a Tankless Water Heater?

Gas water heater is white

Unfortunately, there is no direct answer to this question. In fact, the propane used by a gas tankless water heater will depend on a multitude of factors. These include the type of tank you purchase, the amount of water you use, your water quality, the exterior temperature, and any additional components you’ve attached to the tankless hot water heater.

How Does a Tankless Water Heater Work?

To understand the amount of propane your tankless water heater uses, it’s important to understand how the device actually works. We’ll give a simplified explanation here.

A tankless water heater heats the water as it passes through the device. Water is fed to your house by the plumbing, and the tankless unit is installed along your water pipes. As the water passes through, it’s heated and then fed to your faucets and taps. Gas or electricity can be used to power the tankless heater. Obviously, in this article, we’re talking about a tankless heater that uses propane gas.

Propane is a popular choice as a clean burning fuel, and it’s actually very energy-efficient. A propane water heater can also be economically efficient. However, the amount of propane used will still depend on a few factors, which we’ll examine next:

Determining Factors for How Much Gas a Tankless Water Heater Uses

Not all tankless water heaters are created equal, and neither is the environment they operate in. As a result, the amount of propane used by your gas-powered tankless water heater will depend on several factors, including:


The exterior temperature of your home will play a huge role in determining the gas burned by your tankless water heater. Because the gas water heater is fed water from your home, it will have a tougher job heating up water that is colder. In other words, the colder the water fed into the tankless water heater, the more gas that needs to be burned to heat it up.

This is primarily determined by the exterior temperature of your home. The colder the outside temperature, and the colder the ground water, the more propane needs to be used to heat an equal amount of water running through the system. You can expect to burn more propane during colder months or if you live in a colder area of the world.

IMPORTANT NOTE: This also means that you won’t be able to use as much hot water at once when it is cold out, because the device will struggle to keep up with all your hot water needs, like if you want to run more than one shower during the winter.

Water Quality

The propane burned will also depend on your water quality. Particularly, how “hard” or “soft” your water is. Hard water means that there are more minerals present from your water supply. If this is the case, you might need to install a water softener. It also uses propane to run, if you choose to buy a gas-powered unit. While it’s not technically a part of your water heater, it is still a relevant consideration in calculating the cost to run your hot water. If you choose to install a water softener, you’ll have to include this in your calculations.

Water softeners perform a valuable service in filtering out sediment so that it doesn’t clog your pipes or the water heater itself.

Do You Have a Recirculating Pump?

 Some homes also choose to install a water recirculating pump for their tankless water heater. This is because after water has passed through the water heater, and after you’ve turned off the faucet, this water might just be sitting in your pipes. This water becomes cold before you turn the tap back on. A recirculating pump takes this cold water and pumps it back through the water heater while the faucet or tap is turned off. This keeps all water warm.

A recirculating pump might also be powered by propane gas. But even if not, it will cause your tankless water heater to run more frequently, which will also increase propane gas consumption.

How Much Does It Cost to Run a Tankless Water Heater?

Now that you understand the factors which influence your hot water heater’s gas consumption, it’s time to calculate your propane usage. Doing so is not a very difficult task, you just need to monitor two important variables: hot water usage per month and propane usage per month.

To calculate hot water usage, see how long the device was running over an entire month. Then, check the “gallons per minute” of hot water production, which will be indicated by the manufacturer. Multiply this figure by the minutes the machine was in service.

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Once you have these two figures, you can calculate how much propane was used for a month’s worth of hot water. You can calculate the amount of hot water produced per gallon of propane with the following calculation: total hot water used per month/total propane used in gallons per month. Then, use the total cost of the propane, the money you actually spent, to determine the cost per gallon of propane.

Now you have a useful variable for determining how much it costs to run your tankless water heater! This will be useful for calculating your needs going forward, and setting a hot water budget.

Generally speaking, for a family of three-to-four people, you’ll need about 25 gallons of propane for your monthly tankless water heater needs. This is a good starting point, and you can adjust your usage based on the factors above.

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