How Long Will A 100-Gallon Propane Tank Last For Heating? (Calculated)

For heating, we use various residential propane tank sizes. 100-gallon propane tank is the smallest of these tanks. We are going to look into how long will a 100-gallon propane tank last for heating a house.

The math here seems simple at first. For example, if we use 2 gallons of propane per day for heating, the 100-gallon propane tank will last for 50 40 days. That’s because, due to the 80% tank rule, a 100 gallon when full doesn’t contain 100 gallons of propane; it contains 80 gallons of propane (safety measure).

how long will a 100 gallon propane tank last
A 100-gallon propane tank dimensions are 72″ x 18″ x 20″. This tank can hold 80 gallons of propane.

In practice, however, we need to look into our heating needs. These primarily depend on the size of our house (square footage). As we will see further on, if we take average US household size and propane consumption, 100-gallon propane will last anywhere from 11 days to 85 days (almost 3 months).

To calculate how long does 100-gallon propane last, we need to be aware of the following metrics:

  • 1 gallon of propane contains 91,500 BTU of heating energy.
  • 100-gallon propane tank (when 100% full) contains 80 gallons of propane. This is a safety measure; if a 100 gallon would contain 100 gallons of propane, the pressure on the interior wall of the propane tank at higher temperatures could be dangerously high.
  • These 80 gallons of propane contain 7,320,000 BTU of heating energy.

There are two ways how we can calculate how long will a 100-gallon propane tank last:

  1. By heating demand. Example: Let’s say you need 10,000 BTU/h to heat your house. That means that a 100-gallon propane tank will last for 7,320,000 BTU ÷ 10,000 BTU/h = 732 hours; that’s 30.5 days or about 1 month.
  2. By house size (500 sq ft to 4,000 sq ft houses). Here we use average winter propane consumption per sq ft (0.34 gallon/sq ft; based on average usage). Example: An average 1,000 sq ft house will require 340 gallons of propane for 6 months of heating (from October to March). That means that a 100-gallon tank will last for about 42 days.

We will show you how to do both calculations. If you know your heating demand (anywhere from 10,000 BTU/h to 200,000 BTU/h), you should follow the 1st calculation.

The simpler way to get an idea of how long will a 100-gallon tank last is to look at the 2nd calculation, based on average propane consumption and house size.

Note: You can check how long do all propane tanks (from 1 lb to 2,000 gallon) last here.

Let’s start with the 1st theoretical calculation, and we’ll follow with the 2nd calculation (home size based) that’s much more practical:

1st Calculation: How Long Will 100-Gallon Propane Tank Last (Based On Heating Need)

This one is pretty simple in theory. We only need two figures to calculate how long should a 100-gallon tank last. These are:

  1. 100-gallon propane tank contains 7,320,000 BTU of heating energy. This is the easy part.
  2. What is your average heating need? This could be 10,000 BTU/h, 20,000 BTU/h, 30,000 BTU/h, and so on. This is the hard part: it’s not all that easy to evaluate what your average need is.

If you do figure out how many BTU/h you burn throughout the winter, you can easily calculate how long will a 100-gallon tank last.

Example: Let’s say that we need on average 20,000 BTU/h to heat our house in the winter months. We know that a full 100-gallon propane tank contains 7,320,000 BTU. Assuming 100% efficiency (in reality, the efficiency of burning propane is about 98%), we can calculate how many hours/days will 100-gallon last like this:

100-Gallon Tank Lasts For = 7,320,000 BTU ÷ 20,000 BTU/h = 366 Hours

That’s about 15 days or half a month.

Here is a calculated table of how long will 100-gallon propane last if we know the heating need (BTUs/h):

Heating Need (BTU/h): 100-Gallon Tank Lasts For:
5,000 BTU/h 61 days
10,000 BTU/h 31 days
20,000 BTU/h 15 days
30,000 BTU/h 10 days
40,000 BTU/h 8 days
50,000 BTU/h 6 days

In many cases, this 1st calculation is theoretically sound but very impractical. That’s because it’s almost impossible to determine how many BTUs/h we need (on average) during a 6 month heating period.

That’s when determining how long a 100-gallon propane tank should last, we use the 2nd calculation (based on home size):

2st Calculation: How Long Will 100-Gallon Propane Tank Last (Based On House Size)

Because adequately evaluating heating needs in BTUs/h is very hard, it’s easier if we use average propane consumptions.

As we have written in our article about how long does any propane tank last, we can take two statistical measurements to determine average house propane consumption:

  1. An average US household consumes about 750 gallons of propane per heating season.
  2. An average US household size is 2,200 sq ft.

Based on this, we can calculate that we, on average, need 0.34 gallons of propane per sq ft per heating season. Here is the calculation:

750 Gallons Of Propane ÷ 2,200 Sq Ft House = 0.34 Gallon Of Propane Per Sq Ft

This is a very useful estimation. We can now estimate how long will a 100-gallon tank for 500 sq ft, 1,000 sq ft, 2,000 sq ft houses, and so on.

You will find a calculated table for the most common house sizes below. First, let’s solve one example to illustrate how you can use this estimation.

Example: Let’s say we have a 1,500 sq ft house. We know that, on average, we will need 0.34 gallons of propane to heat 1 sq ft during the heating season. How much propane do we need for the whole 6 months of heating?

Heating Season Needs = 1,500 sq ft × 0.34 gallon/sq ft = 510 Gallons Of Propane

That means that an average 1,500 sq ft house will burn through 510 gallons of propane in a 6-month long heating season (180 days).

We know that a 100-gallon tank contains 80 gallons of propane. This will not last for the whole heating season but it will keep the heat on for some time. How long exactly? Here’s how we calculate that:

100-Gallon Tank Lasts For = (80 Gallons ÷ 510 Gallons) × 180 Days = 28 Days

That means a 100-gallon tank will last for about a month if we use it to heat an average 1,500 sq ft home.

What about smaller 500, 1,000 sq ft homes, or bigger 2,000, 3,000, 4,000 sq ft houses?

Here is the calculated table of how long will a 100-gallon tank last for all of these home sizes:

Home Size (Sq Ft): 100-Gallon Tank Lasts For:
500 sq ft 85 days
1,000 sq ft 42 days
1,500 sq ft 28 days
2,000 sq ft 21 days
2,500 sq ft 17 days
3,000 sq ft 14 days
3,500 sq ft 12 days
4,000 sq ft 11 days

We hope this illustrates a bit how long will a 100-gallon tank last. You can check out a similar calculation for:

2 thoughts on “How Long Will A 100-Gallon Propane Tank Last For Heating? (Calculated)”

  1. I am trying to understand what the cost would be for my home.
    I heat my cellar, and the upstairs. I buy 700 gals of oil each year, For the last 32 yrs..
    Where I have room I am trying to figure out if adding a propane boiler in line with the oil boiler would I save anything using propane?
    I understand they say the cost to switch is $3000-$8000. I am not switching I am just adding a boiler. Would that bring dow the cost?

    • Hello Tom, this really comes down to the cost of oil vs the cost of propane. 1 gallon of heating oil can generate 138,690 BTU. 1 gallon of propane can generate 91,500 BTU; that means that heating oil holds about 51% more energy than propane.

      Now, the costs of both oil and propane are quite volatile. According to Statista, the average price of heating oil in 2021/22 winter is $3.39 per gallon. According to EIA, the residential price of propane in the same period is $2.73 per gallon. That means that heating oil is 24% more expensive than propane per gallon.

      The net would be that, due to higher energy content, using heating oil is about 27% less expensive than using propane. Given the current prices, it’s much better to use heating oil than propane. Getting a new propane tank is financially not a viable option but prices of these commodities can change pretty rapidly. Hope this helps a bit.


Leave a comment