What Is Therm?
A therm is a unit that measures heat energy. It is most often used to measure how much energy you get from natural gas. Many gas companies use therms on their bills to show how much gas energy you used in a month.
Definition
A therm is a large amount of heat energy. In science it is defined as
- 1 therm is equal to 100000 British thermal units or BTU
- 1 therm is about 105.5 megajoules or 105500000 joules
- 1 therm is about 29.3 kilowatt hours of energy
The therm is not an SI unit. The official SI unit for energy is the joule. But the therm is still very common in business and on home gas bills because the numbers are easier to read than very large joule values.
History / Origin
The therm came from work with gas and heat in the early 1900s in the United Kingdom. Gas companies needed a simple way to measure and charge for the heat energy in coal gas and later in natural gas.
Scientists already used the British thermal unit BTU to measure heat, so the therm was set to be exactly 100000 BTU. This made it a handy round number. Over time, gas companies in the United States, the United Kingdom, and parts of Europe began using the therm for pricing and contracts.
Later, the world moved toward the SI system that uses joules. However, therms stayed in use for gas because people were used to them and they matched real life gas usage well.
Symbol & Abbreviation
The therm has a few symbols and ways to write it. The most common ones are
- thm is the usual short symbol used by gas companies
- therm or Therm is often written in full words
- US therm for the version used in the United States
- EC therm or therm EC for the version that followed European rules
On your gas bill you will most often see therms written as Therms or thm.
Current Use Around the World
The therm is mainly used for natural gas and other gas fuels. Its use today is different from country to country.
- United States Many gas companies bill homes and businesses in therms. Your bill may show how many therms you used and a price per therm.
- United Kingdom The therm used to be common for gas, but now gas is often measured and billed in kilowatt hours. The therm is still seen in older documents and some contracts.
- European Union Energy is mostly measured in joules or kilowatt hours. The therm is less common but may appear in older gas trade agreements.
- Other countries Some countries that buy or sell gas internationally may still use therms in trade, but for most science and engineering work they use joules or kilowatt hours.
Although the therm is not an official SI unit, it remains important because so many gas billing systems were built around it.
Example Conversions
Here are some clear examples to help you understand the size of one therm.
- Therm to joules 1 therm is about 105500000 joules
- Therm to megajoules 1 therm is about 105.5 megajoules
- Therm to kilowatt hours 1 therm is about 29.3 kilowatt hours
- Therm to BTU 1 therm is exactly 100000 BTU by definition
- Therm to calories 1 therm is about 25200000 calories small calories
- Therm to food calories 1 therm is about 25200 food Calories the kind shown on food labels
To get a feeling for this amount of energy
- If a 1 kilowatt electric heater runs for about 29 hours, it uses close to 1 therm of energy.
- Many homes might use a few therms in a summer month and many more therms in a cold winter month, depending on climate and house size.
Related Units
The therm is related to many other energy units.
- Joule J The main SI unit for energy. 1 therm is about 105500000 J.
- Megajoule MJ One million joules. 1 therm is about 105.5 MJ.
- British thermal unit BTU A heat unit used in heating and air conditioning. 1 therm is 100000 BTU.
- Calorie cal A small heat unit often used in chemistry. 1 therm is about 25200000 cal.
- Food Calorie kcal The unit used on food labels. 1 therm is about 25200 kcal or Calories with a capital C.
- Kilowatt hour kWh A common unit on electric bills. 1 therm is about 29.3 kWh.
- Therm equivalent units In gas trade, people may also use cubic meters or cubic feet of gas, but they must convert those volumes into therms or joules based on gas quality.
FAQs
What is a therm on my gas bill
On a gas bill, a therm shows how much heat energy you got from the gas you used. The company measures the volume of gas, then converts it into therms using the energy content of the gas. The total charge is usually the number of therms times the price per therm plus extra fees and taxes.
How many kilowatt hours are in one therm
One therm is about 29.3 kilowatt hours. If you know your gas use in therms, you can multiply by 29.3 to estimate the same energy in kilowatt hours.
Is the therm an SI unit
No. The therm is not an SI unit. The SI unit for energy is the joule. However, therms are still widely used in the gas industry and on home gas bills because they are convenient.
What is the difference between a therm and a BTU
A BTU is a smaller energy unit. A therm is a large block of energy equal to exactly 100000 BTU. So if you know energy in BTU, you can divide by 100000 to get therms.
Why do some countries prefer kilowatt hours instead of therms
Many countries use kilowatt hours because they already use them for electricity. Using the same unit for both gas and electricity makes comparing and adding different energy sources easier for customers and regulators.
How big is a therm in everyday life
A therm is a fairly large amount of energy. If you run a 2 kilowatt electric heater on full power, it would take about 14 to 15 hours to use 1 therm of energy. A typical home might use tens or even hundreds of therms during a cold winter season.
Why was the therm created
The therm was created to give gas companies and customers a simple, clear way to talk about large amounts of heat energy. Using 100000 BTU as the base made it easier to handle real life gas use and billing without very long numbers.
