What is a BTU?

BTU stands for British Thermal Unit for the measurement of heat/thermal energy. One BTU is equal to the amount of heat energy used to heat about one pound of water with ever one degree Fahrenheit rise in temperature.



Moreover, BTU is also equal to two hundred and fifty two heat calories and about 1/3 of watt hour. These units can work in reverse too which means that a BTU can also amount to the same amount of energy needed to lower the temperature of the same one pound of water by one degree Fahrenheit fall in the temperature.

However, BTU are very rarely used in Britain nowadays as it is considered to be a non metric measurement. Even in the small number of countries that use BTU as their standard measurement unit have some disagreement over it. The heat energy required to raise the temperature of one pound of water by one degree Fahrenheit can vary according to the method used of heating and the original temperature, which means that it is quite possible to attain a number of different BTUs from a same source. This, however, rarely has any palpable effect on the product information, which is why it is not taken into much consideration.

In United States, however, the BTU is standard measuring unit of heat energy and is commonly used for the comparing of fuels. Since the energy content is different in every country and the fuels come from different places, the BTU content varies accordingly. The BTU content provided in the conversions section and used in the energy calculator reflects the average amount of energy of fuels consumed in the United States of America.

Practical Applications of BTU

Most of the HVAC professionals make use of BTUs for the measurement of the cooling capacity of an air conditioner. The higher the measurement in BTUs is, the greater the power of the air conditioning system is and well, of course, the expensive the unit will be too. Air conditioning systems typically have a power of 1000 BTUs.

When BTUS are used to measure or describe a unit of power, such as in air conditioners, it is written as BTU/h that is, British Thermal Unit per Hour. For example, an air conditioning unit with 1000 BTU/h, provides 1000 BTUs per hour to cool down a house.

Many cooling and heating systems are able to produce up to thousands of BTUs per hour. A unit measurement known as MMBTU is equal to that of a million BTUs. Only a few man made machines are capable of generating this much power and level of heat energy.

When shopping for a cooling or heating system, remember that even a small window-mounted cooling system or heater can give you up to thousands of BTUs per hour. The BTUs can be used as a way to compare the various systems. More expensive and bigger systems will generally have more BTUs as compared to smaller and cheaper ones.

BTU should never be confused with BOTU which stands for the Board of Trade Unit and is a much bigger quantity of energy (3412 BTU).

Nowadays, BTU meter is used to measure the energy of a liquid flow in BTUs (British Thermal Units). These meters are made use in chilled water systems for industrial and commercial purposes. These BTU meters are used to inform the uses of much energy have been used and then charges them accordingly.
Conversions to other units of measurement

One BTU is equivalent to:

  • 1054 to 1060 Joules
  • 252 to 253 calories (small, cal)
  • 0.252 to 0.254 Kcal (Kilocalories)
  • 778 to 782 ft- lbf (foot pounds force)

BTUs, when used as a unit for power for cooling and heating systems is used in the form of BTU/h , which is the correct unit:

  • One watt is equal to 3.41214 BTU/h
  • 1000 BTU/h is equal to 293.07 W ( approximately)
  • One horsepower is around 2544 BTU/h.

In terms of natural gas,

  • One convention of MMBTU is equal to 1.054615 GJ
  • The energy content of a the volume of natural gas yields around 1030 BTU depending on the quality of gas when it is burned,
  • 1000 ft cube of natural gas yields around 1 MMBTU.

How many BTUs per hour will be enough for your home cooling unit?

TO know how many BTUs are required to buy the right air condition system; you first need to calculate the size of the space where you need the cooling system fixed. To calculate the whole house’s square footage, just measure along the two most outside walls of your house.

For an irregularly shaped house were rooms are mostly protrude, take only one measurement for the basic rectangle or square of the house, a spate measurement of the room will not be needed in the calculations.

With, finally your square footage calculation result in hand, multiply the answer by thirty five to get to the estimated value of the BTUS required to cool down your house. Below are a few tips for you, when buying a cooling system:

  • If the lounge is shaded, reduce the number of BTUs you require by at least ten percent.
  • If the living room is sunny, add another ten percent BTUs or see for other ways to shade the room such as with curtains.
  • If you require a cooling system for your kitchen, add another four thousand BTUs to the required value as kitchen appliances tend to generate a lot of eat energy.
  • If two or more people spend a lot of time in the dining or living room, add about six hundred more BTUs per person to cool the particular room down.

The ability of a system to cool the surrounding air is linear with changing BTU (external factors do come to play), but that may not be the only consideration here. Manufacturers of air condition systems provide you with a chart showing the give room size with a BTU rating that can cool it properly. But remember, these are just theoretical results; they did not test these cooling systems in your house. Factors like the outside temperature, obstruction in the circulation of air and exposure t the sun, all can matter when buying a cooling system.

The next confusing thing is that the rooms are to be measured in square feet which only comprise of the floor size. But since rooms are 3 dimensional, they also have height. Air condition systems do not cool the floor; they cool the surrounding air that occupies the entire room. The volume of a particular room depends mainly on the height of the room, making it an important factor.

The external factors mentioned above should be taken in consideration when finding how many BTUs you require in a cooling system. Basically, it will not be a bad idea to upsize the cooling unit BTU requirements a little above hat is mentioned in the size charts of the manufacturers.

Understanding BTUs Calculators

You will find BTU calculators on almost every website on the internet with connection to heating and cooling systems. But what exactly do these calculators do and how do they work? Let’s take a look at how it is useful in real terms.

However, electrical heating systems are the only generators for British thermal units. Even human bodies can produce BTUs. This amount of BTUs measured is dependent on what kind of activity the person will be engaged in at the moment:

  • While sleeping, a person generates 250 BTU/h
  • At rest 350 BTU/h
  • During office work 420 to 640 BTU/h
  • Walking 1040 BTU/h
  • Exercising 1800 BTU/h

As far as the BTU calculators are concerned, they work by taking all or some of the following factors and measurements into consideration and then use them to find the total BTUS your heating or cooling systems put out, these factors include:

  • Length of the house or room
  • Width of the house or room
  • Height of the house or room
  • Lounge/ dining room
  • Bedroom
  • Common Are/ Kitchen
  • French windows
  • Double glazed glass windows




Divide the result by the number of heating or cooling systems you want to install. The BTU calculator will then give you with the amount of BTUs each system will need to output.

However, keep in mind that the figure the BTU calculator provides is a result with no external factors taken into consideration such as if the room is sunny or shady or is in direct contact with the sunlight or has a kitchen nearby. If you live on top of a hill or in a warm climate, you will have to compensate on the following factors to maximize the output of your system.

Also note that it will always be a better option to overestimate your requirements than underestimating them. You can also lower a systems maximum heat or cooling effect but you cannot in anyway make it generate more heat than what it is manufactured to generate.

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