How Much Propane Does a Tankless Water Heater Use? The Ultimate Guide

Tankless water heaters are a great way to save money on your monthly bill. But, do you ever find yourself wondering – how much propane does a tankless water heater use?

On average, a tankless water heater will use 1.5 gallons of propane per day. However, this number can greatly vary due to the size and efficiency of the unit, as well as the amount of hot water required.

For example, if you have a smaller house and only run your dishwasher once or twice per week, then the amount of gas used by your tankless water heater will be much less than if you were to run it daily.

This article will help you calculate the ideal propane quantity your tankless unit requires and the potential savings you can see when switching from a traditional tank heater to a tankless model.

What Factors Affect the Propane Consumption in a Tankless Unit?

Although tankless units are generally more efficient than their tank-style counterparts, some factors can affect their propane consumption. These factors include size, energy efficiency, usage, and more. They also determine the price of a tankless heater.


The larger the tank’s size, the more propane it will consume. The size also refers to the flow rate of the tank, indicating the gallons per minute (GPM). A higher flow rate suggests more energy requirements for the heater to maintain the desired temperature.

For instance, if you have an 11 GPM tankless propane water heater, it generally uses 199,000 BTUs of energy. Therefore, it will consume more propane than a 7 GPM heater that uses around 75,000 BTU of energy.

Energy Efficiency

Propane tankless water heaters, also known as on-demand heaters, provide hot water while using less energy than most traditional water heaters. The efficiency of these heaters is measured using the EF factor, which ranges from 80% to a maximum of 99%.

The higher the EF, the less propane is used to generate the same amount of hot water. Most energy-efficient models are rated at an impressive 0.99 EF.


The amount of propane used in a tankless water heater depends on the duration of use. For instance, if you are using it for a quick hot shower, the propane usage is less compared to long-term use, such as for a household of four that showers twice a day.

Installation and Maintenance

Poor installation can result in inefficient operation, leading to higher propane consumption. Similarly, proper maintenance is necessary to ensure the system is operating efficiently and to identify and address any potential problems that could increase propane consumption.

How Much Propane Does a Tankless Water Heater Use?

gas water heater boiler

If you know the British Thermal Unit (BTU) rating of your tankless unit, you can calculate the number of propane gallons it will consume. Simply divide the BTU rating of the heater by 91,452 BTUs, which is the amount of heat energy contained in one gallon of propane. This will give you an accurate estimate of how much propane your water heater will need.

It’s important to research and understand your specific tankless water heater to ensure it’s properly sized and configured to your needs. Unlike an electric tankless water heater, the calculation for propane water heaters is slightly complex.

Are Propane Heaters More Efficient than Conventional Water Heaters?

Propane tankless water heaters are a great investment for those looking to gain energy efficiency and save money over the long term.

Compared to conventional water heaters, propane heaters can be up to 22% more efficient, meaning they can heat a given amount of water faster while also providing better temperature consistency.

Though the upfront price of purchasing and installing a propane tank may be higher, the long-term energy savings and performance benefits outweigh the initial cost.

So, is a propane tankless unit worth it? Ultimately, it depends on your needs and budget. Propane tankless water heaters can offer energy savings and an endless supply of hot water, but they come with a hefty price tag and require more maintenance and annual inspection.

What is the Average Price of a Propane Tankless Unit?

Many factors affect the price of tankless units, including the size, power output, and any additional features, such as digital temperature controls. Generally, you can find basic models for as little as $170, while high-output heaters are priced at over $2,000. The larger models can provide sufficient water flow to run two hot showers simultaneously.

How Long Does a Tankless Water Heater Last?

Propane tankless water heaters can last up to 20 years. This is a considerably long lifespan compared to storage tank heaters which only last six to eight years on average. Also, these tankless heaters are more durable than electric units.

How Much Can I Save With a Tankless Water Heater?

On average, you can expect to save around $150 a year, meaning it will take around six to seven years to cover the cost of the tank. After that, you can enjoy hot water virtually for free, though you will need to factor in the price of propane according to the frequency and duration of use.

What are Some Major Issues With Tankless Water Heaters?

The main issue with tankless water heaters is mineral buildup. Over time, minerals from your water supply can build up in the tankless heater, reducing its efficiency and potentially damaging the unit. To combat this, you should flush the heater at least once every six months to remove any mineral buildup and keep the unit working properly.

Another issue that can arise with tankless water heaters is system overload. This occurs when the heater provides more hot water than it is capable of producing. To prevent this, it is important to size the tankless water heater correctly for your family. If the unit is too small, it will not be able to keep up with the hot water demand, resulting in a cold-water sandwich.


If a tankless water heater is sized and installed correctly, it can be a great way to save energy and money. If you’re looking to use this technology as an alternative to traditional tanked systems, you’ll want to make sure you’re getting the most out of your investment by understanding how much propane a tankless water heater uses.

With years of experience under his belt, Adam decided to put his water heater knowledge to work. By providing high-quality content and expert guides, Adam hopes to help anyone looking for expert water heater advice.