Skip to content
What size propane tank for tankless hot water heater? - Heatercamp

What Size Propane Tank For Tankless Hot Water Heater?

    As an Amazon Associate I earn from qualifying purchases. Learn More

    Before discussing the “size of propane tanks” for a tankless water heater, you should know 3 essential facts.

    • All size LPG cylinders come with sufficient gas pressure (PSI) to run any tankless water heater of any size.
    • Larger LPG cylinders can run tankless water heaters for longer, and smaller ones run for shorter.
    • Your regulator will control/adjust the gas flow, not the propane tank.

    A tankless water heater’s gas consumption rate depends on its BTU/hr. 

    Then, how long you wanna run your tankless water heater? That should be your primary concern for choosing a perfect propane tank.

    But how can you calculate the whole thing? Let me reveal everything!

    How big a propane tank do I need for a tankless water heater?

    Propane tanks are attachable with both 

    • Portable tankless water heater
    • Residential tankless water heater

    Propane tank size for portable models

    For portable models, 20lbs propane tank suits me the best.

    Even most American people like attaching a 20 lbs propane tank with their portable water heaters. Cause 20 lbs cylinder takes tiny space to store, and you can move it around effortlessly.

    Also, 20 lbs propane tank is easily mountable outside RV campers, so you can utilize your tankless water heater for outdoor shower and supply hot water for all outing demands.

    But, in case you have an additional attachment to the gas line like a BBQ grill or stove with the same propane tank, a 30 lbs propane tank will be a satisfactory solution.

    However, you should consider both the portability and gas demand in that scenario.

    Finally, you might be wondering if the 20 lbs cylinder is sufficient to produce hot water for a large family or for showering horses and pets?

    Yes, absolutely! 

    The 20 lb propane tank can run a 2.64 GPM portable tankless water heater for 6+ hours in max. Doesn’t it sound more than sufficient?

    Propane tank size for residential water heaters

    At least 4.5 GPM to a maximum of 11 GPM tankless water heaters are suitable for whole-house hot water distribution. 

    Either you may attach a propane tank to run only your tankless water heater (which I’m going to discuss here). 

    Or, some people install gigantic propane tanks CENTRALLY to supply gas to all appliances like cooktops, ovens, space heaters, water heaters, etc.

    Assuming you need to operate the tankless water heater for 2 hours a day, here’s the sizing chart of your propane tank.

    • For a 3 GPM tankless water heater with a small family, 40 lbs propane tank will be sufficient for a month. 
    • For a 6 to 8 GPM tankless water heater with a medium family, a 100lb propane tank will last around 40-45 days
    • For an 11 GPM tankless water heater with a larger family, 100 lb propane tank will last approximately 1 month.

    Note: As it depends on uses, you will undoubtedly find more days than I’ve maintained above.

    On average, an American family uses 300 gallons of propane each YEAR to run all their appliances, and only 40% of that quantity is required for the water heaters. 

    How long will a propane tank last on a tankless water heater?  

    How long will a propane tank last on a tankless water

    Before I show you the chart, here’s a few basic knowledge to identify the gas consumption rate of a tankless water heater. 

    It will help you to calculate precisely how long the cylinder will run your appliances.

    • 1 lbs propane = 21,548 BTUs (Very Nearly)
    • 1 Gallon propane = 91,364 BTUs (Very Nearly)

    Now, think what, if a tankless gas water heater produces 21,548 BTU/hr, how much propane will it consume? 

    You might be thinking it’s 21,548 BTU, and that’s partially true. But here are two more things to take under consideration. 

    Firstly, all tankless water heater has an energy factor, which remains between .82 to .96 depending on brands and their optimization level.

    O.82 means 82% efficiency; similarly, 0.96 stands for 96% efficiency.

    If a tankless water heater has a 96% efficiency level, that means, if it draws 100g propane, it will be able to utilize 96g of it to produce hot water, and the rest 4g will get wasted through exhaust other components.

    How it impacts?

    A camplux 180K BTU tankless water heater offers only 6.8 GPM, with an energy factor of 0.82

    A Rinnai 160K BTU tankless water heater offers nearly 9 GPM cause it’s 96% efficient with an energy factor of 0.96.

    Secondly, no propane tank is refillable 100% of its capacity due to safety. The 20lbs propane tank comes with 80% of its capacity, which means you get around 16lbs LPG inside it.

    Except, there are few brands like “Flame King” who build their propane tank on a slightly larger scale so that you can refill the exact amount of LPG instead of sacrificing that 20%. 

    Let’s calculate how long a propane tank can run a tankless water heater.

    Propane Consumption of Portable Tankless Heater


    MAX BTU/hr

    Propane Consumption lb/hr

    Propane Consumption Gal/hr

    1.32 GPM


    1.299424541 lb/hr

    0.306 Gal/hr

    1.58 GPM


    1.902728792 lb/hr

    0.448 Gal/hr

    2.11 GPM


    2.552441062 lb/hr

    0.601 Gal/hr

    2.64 GPM


    3.155745313 lb/hr

    0.744 Gal/hr

    3.18 GPM


    3.759049564 lb/hr

    0.886 Gal/hr

    4.22 GPM


    5.104882124 lb/hr

    1.303 Gal/hr

    LPG Consumption of Residential Tankless Heater


    MAX BTU/hr

    Propane Consumption lb/hr

    Propane Consumption Gal/hr

    2.64 GPM


    3.155745313 lb/hr

    0.744 Gal/hr

    3.18 GPM


    3.805457583 lb/hr

    0.897 Gal/hr

    5.28 GPM


    6.961202896 lb/hr

    1.641 Gal/hr

    6.86 GPM


    8.353443475 lb/hr

    1.970 Gal/hr

    7 GPM (Rinnai)


    6.03304251 lb/hr

    1.422 Gal/hr

    9 GPM (Rinnai)


    7.425283089 lb/hr

    1.751 Gal/hr

    10 GPM (Rinnai)


    8.353443475 lb/hr

    1.970 Gal/hr

    11 GPM (Rinnai)


    9.235195842 lb/hr

    2.178 Gal/hr

    Now, you have an idea of each type of tankless water heater gas consumption in lb/hr and Gal/hr

    So, you can easily divide your preferred propane tank size (lbs or Gal) with the particular number to find out how many hours the cylinder can run your appliance.

    Note: Nobody uses their tankless water heater in MAX power ever. So, it’s not an indication of how long a full tank of propane will last. 

    If you find that a specific propane tank runs a water heater for 60 hours, that means in real-time, you’ll be able to use that for a minimum of 60×2.5 = 150 hours or nearby.

    What Size Propane Tank Regulator Do I Need To Run Tankless Water Heater?   

    Propane tank regulator size for tankless water heater

    Any standard 11 W.C regulators will work perfectly. 

    Or you can pick a 0-30 PSI adjustable regulator instead.

    But, does an adjustable regulator give you an additional advantage to run a tankless water heater? Absolutely not.

    Here’s the answer.

    Propane pressure is measured in two different matrices.

    • Water Column (W.C)
    • Pound Per Square Inch (PSI)

    Household propane appliances such as tankless water heaters require a maximum of 11 W.C or 0.397003 PSI. Few large appliances consume slightly more fuel; they need a pressure around 0.5 PSI.

    However, the valve of propane appliances such as water heaters and other HVAC appliances can tolerate a maximum of 25 to 60 PSI gas pressure. Keeping it under 30 PSI is the safest choice.

    But, inside the propane tank, gas pressure remains between 145 to 180 PSI which is enormous. So we use a low-pressure regulator to decrease the pressure at a tolerance level.

    However, Increasing the pressure won’t impact on water heater’s gas burner. But decreasing it below the minimum threshold will turn off the heater.

    A tankless water heater contains its own regulator and passes gas inside the burner in a measured range. Raising the gas pressure from the tank regulator won’t increase the flame on the water heater’s burner.

    Your only mission to use the regulator is lowering the gas pressure, which any random regulator can do perfectly.

    So, simply go for a perfect brass regulator that fits your tank and appliance. 

    How do you hook up a propane tank to a tankless water heater? 

    Hooking up a propane tank with tankless water heater

    Propane hose comes with two types of connectors. 

    • POL Connector
    • QCC1/Type1 Connector

    Connecting QCC1/Type1 Connector 

    I do prefer the QCC1/Type 1 because of its simplicity. 

    99% portable tankless water heater comes with a propane hose, so you don’t need to buy one. Almost all of those contain QCC1/Type1 connectors.

    Step 1: Before connecting the hose with the propane tank, you should join the waterline and hose with the water heater. 

    Step 2: Now, make sure the propane tank’s valve is closed. Then connect the QCC1/Type1 connector with the cylinder’s valve. Twist it on the right side to make it tight.

    Step 3: Now, open the cylinder valve and spray soapy water to detect if there’s any leakage. 

    That’s it. You are good to go.

    Connecting a POL Connector

    Step 1: You need to join all the water lines and the hose with the tankless water before connecting it to the tank.

    Step 2: All 20 lbs cylinder has a POL valve inside. First, you need to connect the POL thread with the propane tank. Twisting left will make it tighter.

    Now here’s an essential part.

    Step 3: Open the cylinder valve slightly; then, you will hear a CLICK sound. POL connector has an additional safety valve inside. This valve can detect any leakage on the hose to keep yourself protected.

    Step 4: Once you hear the CLICK sound, you are good to go and allowed to twist the tank valve more as you require. Additionally, you only will be able to hear the click sound if you slowly and slightly open the tank valve. 

    Otherways, the safety valve will remain closed, and you won’t get sufficient pressure with the hose.

    Step 5: Finally, you should do a leakage test using soapy water. If no leakage is detected, you are good to go.

    Dimensions and Gas Holding Capacity of Propane Tanks?    

    Here’s a chart of available propane tanks that we randomly use in America with dimensions, empty and full weight, and gas holding capacity.

    Vertical Propane Tanks

    Size lbs/Gal



    Propane Holding Capacity

    Empty Weight

    Ful Weight

    1 lb

    8.25 inches

    3.75 inches

    0.405 Gal

    1.72 lbs

    2.6 lbs

    5 lb

    12.8 inches

    8.1 inches

    1 Gal

    10 lbs

    14.24 lbs

    10 lb

    17.8 inches

    9 inches

    2.5 Gal

    14 lbs

    24.6 lbs

    11 lb

    13 inches

    12 inches

    2.5 Gal

    13.22 lbs

    23.82 lbs

    20 lb

    18 inches

    13 inches

    5 Gal

    18 lbs

    39.2 lbs

    30 lb

    23.7 inches

    12.3 inches

    7 Gal

    25 lbs

    54.68 lbs

    40 lb

    29.3 inches

    12.3 inches

    10 Gal

    34 lbs

    76.4 lbs

    100 lb

    48.7 inches

    14.7 inches

    25 Gal

    70 lbs

    176 lbs

    200 lb

    41 inches

    24 inches

    50 Gal

    161 lbs

    373 lbs

    420 lb

    54 inches

    30 inches

    120 Gal

    276 lbs

    784.8 lbs

    33 lb

    26.9 inches

    12.3 inches

    8 Gal

    35 lbs

    68.92 lbs

    Horizontal Propane Tanks

    As the horizontal propane tanks are gigantic and used for whole-home propane distribution, I won’t mention it’s empty or full weight. Cause you never need to move them around, or you can’t actually.

    Size lbs/Gal



    Propane Holding Capacity

    20 lb

    18 inches

    13 inches

    5 gal

    50 lb

    28 inches

    12.3 inches

    12.2 gal

    78 lb

    27 inches

    16 inches

    20.3 gal

    79 lb

    48 inches

    19 inches

    20.3 gal

    98 lb

    48 inches

    14.3 inches

    29.3 gal

    250 Gallon

    7 Feet 10 Inch

    30 inches

    200 Gal

    500 Gallon

    9 Feet 11 Inch

    37.5 inches

    400 Gal

    1000 Gallon

    16 Feet 2 Inch

    41 inches

    800 Gal

    Reliable Brands That Rent and Sell Propane Tanks

    Rent vs Buy a propane tank; which one do you prefer?  

    I’ve researched and found that buying a cylinder is logical and worthy for smaller-sized propane tanks like 1lb, 20 lbs, 30 lbs, or even 40 lbs.

    But renting is the best solution for larger cylinders such as 100 lbs, or even 100 gallons, 120 gallons, 250 gallons, 500 gallons, or even 1000 gallons. 

    Thinking why?

    Firstly, when you buy a cylinder, all the responsibility such as refilling it, testing the health, moving it around is totally up to you, which is an extra hassle. 

    But if you rent the cylinder from a good company like frosterfuels, they will do everything for you and almost freely.

    Secondly, buying a giant propane tank and installing it won’t increase the price of your property or its rent, so there’s no additional advantage.

    Here are some excellent brands whom you might rely on.

    Flame King

    For buying smaller propane tanks between 1lbs to 420lbs ranges, the flame king is a fantastic choice. All their cylinders are X-ray and hydrostatic tested, and DOT approved.

    Essentially, they manufacture a refillable 1 lbs canister along with refill kits that will allow you are saving a vast cost running your buddy heaters or portable tankless water heater.

    However, you can refill that canister yourself, again and again, free of cost, and enjoy your winter outings.

    Additionally, flameking has all propane accessories like the hose, gauge, and all you need to operate your appliances smoothly.


    Amerigas is arguably the most famous propane tank rental company that delivers fuel for residential and commercial zones all over the United States.

    They offer services like

    • Site Survey and tank installation
    • Emergency propane delivery and refill
    • Tank health test and recertification
    • Tank maintenance and repair
    • Door to door propane tank delivery

    And many more.

    Especially their service is mindblowing for off-grid locations.


    Forsterfuels is another propane cylinder delivery service like Amerigas. But they offer both selling and rental services.

    Additionally, they offer propane tank refill, checkup, and recertification, moving or re-positioning/installation services totally free.  

    If forsterfuels have access to your location, then it will be a better choice to go.

    Can propane tanks explode?  

    Can a propane tank explode?

    Not really if you don’t do anything unusual or misuse it. 

    A steel cylinder can tolerate 3X more internal pressure than the amount it feels by holding propane.

    Additionally, when refilling a cylinder, always it’s suggested to fill not more than 80%.

    Inside the cylinder, propane remains in the liquid state, and as you know, the gas volume expands with rising temperature. For any ambient temperature, a propane cylinder is totally safe if there’s no leakage.

    If you ensure routine checkups and maintenance and never store the cylinder in any place where the temperature remains above 140F or 60C, there’s no chance of explosion.

    FAQs of Propane Tank for Tankless Hot Water Heater 

    How much does it cost to refill a propane tank?     

    Propane refill cost varies from state to state and remains mostly around $3~$4 per gallon.

    If you get service from a rental company like Amerigas or forsterfuel, they might offer some discount and other facilities.

    How many years can you use a propane tank?  

    In America, a propane tank is allowed to use for 12 years from the day it has been manufactured.

    In Canada, the duration is 12 years.

    But you can recertify that by doing a checkup by a licensed company. 

    According to the method of recertification, the propane tank might be valid to use for the next 5, 7, or even 12 years.

    Does propane go bad? (In case you leave it for long…)  

    No, it never goes bad like kerosene, diesel, or any furnace fuel.

    If there’s no leakage at the valve or the tank, propane is storable up to uncountable long years.

    What is the average size propane tank for a house?  

    300 Gallon is an average size for distributing propane to the whole household appliances.

    In case you want to run only space heaters and water heaters, particularly, the 120-gallon cylinder might be sufficient.

    Can you use a 20 lb propane tank on a water heater?  

    You can use a 20 lb propane tank for portable tankless hot water heaters. It can be used for a whole house water heater too, but in that case, the cylinder won’t last for a longer duration.

    Check my data table above, where I’ve provided data on gallon/hr and lbs/hr gas consumption of tankless water heaters of various BTUs.

    Is it OK to lay a full propane tank on its side?  

    It’s not suggested, especially when the tank remains entirely full.

    Cause if you flip the tank or lay it on its side, propane starts coming out in the liquid form. Additionally, if you know about the refilling process, that’s being done by fliping the mother propane tank so that propane can enter the destination in a liquid form.

    If you require to keep your propane tank laying due to insufficient vertical storage, I recommend choosing a horizontal cylinder instead of a vertical one.