How long a 20lb propane tank lasts depends on the heater you use with it. Depending on how much you use your propane tank, the tank can empty in one day, or in a month.
In this article, we’re going to check all the different possible durations. You just have to look up your heater’s heating power (in BTU per hour).
Quick answer: A 20lb propane tank lasts for 38 hours of heating on a regular 9,000 BTU portable propane heater. On larger heaters (30,000 to 60,000 BTU) it lasts between 6 and 12 hours.
How much propane is in a 20lb propane tank?
A 20lb propane tank contains 16lb of propane gas because it is only filled up to 80% of its capacity.
Propane tanks are generally filled to 80% of their capacity because propane is very temperature sensitive.
With each degree of temperature increase, propane expands 17 times more than air.
So, if you fill a propane tank to 100% of its capacity, the internal pressure varies strongly with the outside temperature.
A propane tank that’s only 80% full has enough room for the propane to contract and expand.
How much energy is in a 20lb propane tank?
Before we can calculate how long a 20lb propane tank lasts, we have to know how much heat energy a 20 pounder contains.
This is important because the propane consumption of propane heaters is typically not specified in pounds of propane gas per hour, but in terms of heat energy per hour.
One pound (lb) of propane contains 21,594 BTU of heat energy. And a propane tank is filled to 80% of its capacity.
A 20lb propane tank, therefore, contains 345,552 BTU of heat energy.
20 lb × 21,594 BTU per lb × 80% = 345,552 BTU
How much energy do different propane heaters use?
Now that you know how much heat energy is stored in a propane tank, let’s check different propane heaters and how much heat energy they consume per hour.
Typically, regular portable indoor propane heaters consume 9,000 BTU – 18,000 BTU per hour.
Examples are my all-time favorite portable propane heaters, the Mr. Heater Buddy (9,000 BTU) and the Mr. Heater Big Buddy (18,000 BTU) (click here to view my review).
Then, larger propane heaters, such as wall- or ceiling-mounted gas heaters or patio heaters consume between 30,000 BTU/h and 55,000 BTU/h.
Of course, there are always exceptions. Some ceiling-mounted propane heaters go up to 80,000 BTU/h or 120,000 BTU/h.
And then, there are also industrial torpedo heaters which consume up to 130,000 BTU/h.
A regular indoor propane heater on moderate settings consumes 10,000 BTU/h. A strong outdoor patio heater consumes 45,000 BTU/h.
How long will a 20 lb propane tank last for regular everyday usage?
So, let’s have a look at how long different heater sizes last on a 20lb propane tank.
The calculation follows the formula:
Tank capacity (in hours) = Propane tank capacity (in BTU) ÷ Heating power (in BTU/h)
where the propane tank capacity is 345,552 BTU, which we calculated earlier.
|Heating power (in BTU/h)||Tank capacity (in hours)|
|3,000 BTU/h||115 hours|
|6,000 BTU/h||58 hours|
|9,000 BTU/h||38 hours|
|12,000 BTU/h||29 hours|
|15,000 BTU/h||23 hours|
|18,000 BTU/h||19 hours|
|21,000 BTU/h||16 hours|
|24,000 BTU/h||14 hours|
|27,000 BTU/h||13 hours|
|30,000 BTU/h||12 hours|
|33,000 BTU/h||10 hours|
|36,000 BTU/h||10 hours|
|39,000 BTU/h||9 hours|
|42,000 BTU/h||8 hours|
|45,000 BTU/h||8 hours|
|48,000 BTU/h||7 hours|
|51,000 BTU/h||7 hours|
|54,000 BTU/h||6 hours|
|57,000 BTU/h||6 hours|
|60,000 BTU/h||6 hours|
|70,000 BTU/h||5 hours|
|80,000 BTU/h||4 hours|
|90,000 BTU/h||4 hours|
|100,000 BTU/h||3 hours|
|110,000 BTU/h||3 hours|
|120,000 BTU/h||3 hours|
|130,000 BTU/h||3 hours|
According to the calculations:
- A regular indoor propane heater lasts 38 to 115 hours, depending on the heat settings.
- A patio heater lasts for 6 to 9 hours of heating on a 20lb propane tank.
- Industrial-grade heaters last for only 3-4 hours on a 20lb propane tank. You should use them with larger tanks instead.
How long does a heater last on a 20lb propane tank (depending on daily heating duration)?
The results from the table above show how long you can run different heaters on a 20lb continuously.
A regular portable propane heater or indoor heater, according to the table lasts anywhere between 32 hours and 115 hours.
However, you never run a propane heater continuously.
So, how long would a regular heater last on a 20lb propane tank realistically?
Here’s a table with how long a regular indoor heater hot enough to keep a large living room warm (9,000 BTU), lasts on a 20lb propane tank realistically, depending on how much you use the heater.
|Daily heating duration (in hours)||How long does a 20lb propane tank last? (with a 9,000 BTU/h heater)|
|2 hours||19 days|
|4 hours||10 days|
|6 hours||6 days|
|8 hours||5 days|
|10 hours||4 days|
|12 hours||3 days|
|14 hours||3 days|
A 20lb propane tank lasts for a week of heating if you use it for 4-6 hours a day.
If you use your heater as the main heat source and you use it for 12 hours a day, a 20lb propane tank lasts you 3 days.
How to ensure your tank lasts as long as possible
Now that you know how long your propane tank lasts, let’s have a quick look at how you can maximize the heating duration you get from your tank.
First, the propane consumption is directly proportional to the heat setting you choose.
So, if you cut the heat setting in half, the propane consumption halves as well, which, in turn, doubles the heating duration.
My propane heater has two heat settings: 4,500 BTU and 9,000 BTU. I run my propane heater on the lower setting. And it’s still hot enough to keep me warm all the time!
Also, ensure that the gas line and the heater are connected tightly, so no gas leaks.
And, always use a high-quality, weather-proof gas hose such as Gaspro gas hose (click here to view it on amazon).
Never use an old gas hose, since they can form micro-leaks over time. You won’t notice them, but even if they leak only 0.1% of your propane tank a day, that’s a wasted tank every 3 years!
Check out this article: How to fix a propane heater using too much propane (click here) for more propane-saving tips!