Propane is a key energy source in any RV. If you want to cook food, run a furnace, power a propane generator, or otherwise ensure quality time during your journey, you need to have adequate propane supplies.
What’s the right RV propane tank size for you? How much do you really need? How RV propane tank sizes impact how long they last? We are going to answer these and some other questions below.
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Propane tank types
Let’s begin with propane tank types. The propane tank-type doesn’t impact how efficiently propane is used, but distinguishing between them is important because they have varying propane capacity.
There are two kinds of propane tanks – ASME tanks and DOT cylinders. DOT cylinders are the tanks that you would use to fuel a barbecue or RV grill.
ASME tanks are most often used on motorhomes. These tanks are mounted directly to the frame of the RV, which makes them not removable. To refill an ASME tank, you need to drive the entire RV to a propane station.
DOT cylinders are commonly used on travel trailers, fifth wheels, and some small motorhomes. These propane tanks are mounted either to the tongue or bumper of the RV or in one of its exterior compartments. DOT cylinders are removable, so you don’t have to bring the RV to a propane station – you can simply take the tanks out and bring them to the station to refill them.
ASME tank sizes can vary significantly from motorhome to motorhome. A smaller class C motorhome may have just one 20-pound ASME propane tank, while a large class A motorhome may come with a tank holding over 100 pounds of propane.
DOT cylinders are usually much smaller. However, because you can easily mount several DOT cylinders in an RV, the total propane capacity can be higher than in large ASME tanks.
Not only that, but expanding a DOT cylinder propane system is much easier than with an ASME system. Whether you will be able to expand your propane tank setup and how much you can expand it depends on your RV though.
RV Propane tank sizes
Now that we’ve gotten propane tank types out of the way, let’s talk about propane tank sizing.
If you are new to the RV propane thing, then you are probably confused about the measurements of propane tank sizes. Some tank sizes are measured in gallons and others in pounds.
Typically, propane tanks are referred to by their weight – that is, how many pounds they weigh when full. However, larger tank sizes may be referred to by their capacity in gallons.
Below are the most common propane tank sizes. One important thing to keep in mind is that propane tanks are usually filled up to 80% of their full capacity. This is done to provide room for propane’s expansion in the tank so that it doesn’t blow up on you. This means that you will never be able to make use of a propane tank’s full capacity, which you need to consider when doing any calculations.
20 lb tank
20-pound propane tanks measure 18 inches in height and 12 inches in diameter. They hold roughly 5 gallons of propane. Thanks to their lightness, these tanks can be carried by one person. If you didn’t know, 20-pound propane tanks are very commonly used with grills and barbecues.
33 lb tank
33-pound tanks hold roughly 8 gallons of propane and measure 2 feet in height by 1 foot in diameter. A little heavier than 20-pound tanks, these tanks can still be carried by one person.
100 lb tank
100-pound tanks hold 25 gallons of propane when full. They usually measure 4 feet tall and 18 inches in diameter. These tanks may still be carried by one person, but most people will probably want a buddy to help with its transport.
420 lb tank
420-pound tanks hold 100 gallons of propane. These huge tanks measure 4 feet in height by 3 feet in diameter. Needless to say, such tanks are no longer portable.
Calculating how much propane you need
Above, we overviewed a few propane tank sizes commonly used in RVs. There are many more size options out there, but we think that there is no real point in listing them all. What’s much more important is trying to understand how much, say, a 100-pound tank is going to last in RV applications.
Here, to our help will come the so-called British thermal units, which essentially indicates how much energy a system produces per hour.
Pivotal here is that a gallon of propane has a burn rate of around 92,000 BTUs per hour. If you know exactly how much BTUs your RV appliance produces, then it will be very easy for you to calculate how much your propane expenditure will be.
Let’s overview a couple of examples so that you know how to calculate your propane expenditure.
RV furnace
RV furnaces usually have an energy output of 30,000 BTUs, though some RVs have 20,000 or 15,000 BTU furnaces.
Calculating how many gallons a furnace will use up in an hour is very simple – you just need to divide the furnace’s energy output by propane’s energy output per hour. For example, a 30,000BTU furnace would use a little less than 1/3 of a gallon if left to run for an hour – 30,000BTU/92,000BTU = 0.326 gallons per hour.
Likewise, a 20,000BTU furnace would use around 0.22 gallons of propane per hour, while a 15,000BTU furnace would use about 0.16 gallons.
It’s also easy to calculate how long a gallon of propane will last – you need to divide the energy output of a gallon of propane by the energy output of your appliance. For example, one gallon of propane would be able to power a 30,000BTU furnace for about 3.067 hours – 92,000BTU/30,000BTU.
You could go a little further and calculate the number of days your propane inventory will last. This is done with the following formula:
(((92,000BTU x gallons of propane)/BTU of appliance)/hours per day)
For example, if you have 5 gallons of propane and intend to use your 30,000 BTU furnace an hour per day, then those 5 gallons will last you 15.33 days!
One thing to keep in mind here is that the 30,000 BTUs in our example is the energy output of an RV furnace at maximum heat settings. If you lowered the heat output, you would be able to use your furnace for a longer time!
Not only that, but you often don’t have to keep the furnace on for hours. It’s usually enough to turn it on for a couple of minutes to receive heating for several hours. Due to this, propane can be much more efficient than we’ve demonstrated, especially if you set the goal of using your furnace as little as possible.
By the way, if you are trying to calculate how many hours of furnace/grill/stove use you can get out of a propane tank, make sure to use 80% of the tank’s fuel capacity as the basis of your calculations. As we’ve mentioned above, propane levels are kept below 80% for safety reasons, and if you make calculations on the tank’s full capacity, you are going to get unrealistic and unachievable numbers.
Grills, barbecues, and burners
With grills & barbecues, you would follow the same logic as with RV furnaces when calculating propane expenditure.
Most grills use standard 20-pound propane tanks, which can provide between 18-20 hours of grilling time. Larger grills may burn through a propane tank in a mere 10 hours.
Home stoves usually have a BTU of 7,000 per burner. Since RVs typically have 2- or 3-burner stoves, you could expect your stove to have a potential of 14,000-21,000BTUs, which means that if you use all the burners, one gallon would last you 4.4-6.6 hours.
How to measure propane consumption?
It’s nice to be able to calculate how much propane you will need to run your furnace for say 1 hour per day, but in reality, things aren’t as easy, unfortunately.
Often, you can’t precisely calculate your exact propane consumption because you don’t really know how many BTUs your grill of furnace consumes. The manufacturer may not have provided you with numbers, or maybe you only have the maximum energy output, which isn’t very useful since you will probably only rarely set your furnace to its maximum heat output setting.
Fuel gauge
The easiest and most reliable way of measuring how much propane there is left in the tank is using a fuel gauge. Many tanks come with a gauge preinstalled, but even if yours doesn’t, you could easily purchase one online or in a local store.
Tank fuel gauges usually indicate the remaining fuel in percentages, so you will need to do some calculations to find out how much propane there is actually left. It’s easy – you just need to multiply the full capacity of your fuel tank by the percentage shown on the fuel gauge.
You may also follow the chart below for a quick estimation of the remaining fuel level:
| Reading | Fuel remaining | ||||||||
| 5 | 10 | 20 | 40 | 100 | 150 | 200 | 250 | 500 | |
| 80% | 4 | 8 | 16 | 32 | 80 | 120 | 160 | 200 | 400 |
| 70% | 3.5 | 7 | 14 | 28 | 70 | 105 | 140 | 175 | 350 |
| 60% | 3 | 6 | 12 | 24 | 60 | 90 | 120 | 150 | 300 |
| 50% | 2.5 | 5 | 10 | 20 | 50 | 75 | 100 | 125 | 250 |
| 40% | 2 | 4 | 8 | 16 | 40 | 60 | 80 | 100 | 200 |
| 30% | 1.5 | 3 | 6 | 12 | 30 | 45 | 60 | 75 | 150 |
| 20% | 1 | 2 | 4 | 8 | 20 | 30 | 40 | 50 | 100 |
| 10% | 0.5 | 1 | 2 | 4 | 10 | 15 | 20 | 25 | 50 |
Without a fuel gauge
If you don’t have any fuel gauges on your propane tank, there is another way for you to measure your propane consumption. But it is inexact, and you will need to go through trial and error in order to reach the desired propane use efficiency.
So, suppose you’ve run your furnace for 1 hour, and you want to see how much propane has been used. To do this, you need to follow these steps:
- Determine the tare weight of your propane tank (the weight when empty). You should be able to find this figure on a stamp on the tank.
- Figure out the weight of the tank with the remaining propane in it.
- Calculate the difference between the tank’s current weight and its tare weight. The weight difference is the weight of propane left in the tank.
- Divide the weight of propane by 4.24. 1 gallon of propane weighs 4.24 pounds, which is why you do this division.
It doesn’t really matter which method you use. What matters is your ability to approximate how much propane you’ve used when, say, running your furnace for an hour at 50% of its output.
As we’ve mentioned above, it’s difficult to precisely calculate how long a 10-gallon tank will last you. You may approximate one number before buying a tank but get a whole another figure after using the tank for some time.
Due to this, you should use your pre-purchase calculations as just a basis for choosing a propane tank. But you also need to keep in mind that those calculations may not necessarily transfer to actual tank use because it’s difficult to calculate exactly how much BTUs your appliance is producing.
Bottom line
Hopefully, the guidelines above are sufficient so that you get a properly sized propane tank for your RV.
If you are new to this RV thing, then you probably shouldn’t worry too much about tank sizes just yet. You sure can try to estimate how much propane capacity you need in the RV, but RVs often come with adequate propane storage, and you may not even need to worry about it.
After using your RV for some time, you will be able to tell whether you really need to get a new propane tank or add a couple of additional tanks to your existing system. It all comes down to your propane use pattern, and if you’ve just bought an RV, you can’t know whether its current capacity will be enough or not.
Check out our RV how-to guides for more articles like this.
