Which BTU is needed for my home

What is a BTU?

The British Thermal Unit, or BTU, is an energy unit. It is approximately the energy needed to heat one pound of water by 1 degree Fahrenheit. 1 BTU = 1,055 joules, 252 calories, 0.293 watt-hours, or the energy released by burning one match. 1 watt is approximately 3.412 BTU per hour.

BTU is often used as a point of reference for comparing different fuels. Even though they're physical commodities and quantified accordingly, such as by volume or barrels, they can be converted to BTUs depending on the energy or heat content inherent in each quantity. BTU as a unit of measurement is more useful than physical quantity because of fuel's intrinsic value as an energy source. This allows many different commodities with intrinsic energy properties to be compared and contrasted; for instance, one of the most popular is natural gas to oil.

BTU can also be used pragmatically as a point of reference for the amount of heat that an appliance generates; the higher the BTU rating of an appliance, the greater the heating capacity. As for air conditioning in homes, even though ACs are meant to cool homes, BTUs on the technical label refer to how much heat the air conditioner can remove from their respective surrounding air.

 

Size and Ceiling Height

Obviously, a smaller area room or house with shorter lengths and widths requires fewer BTUs to cool/heat. However, volume is a more accurate measurement than area for determining BTU usage because ceiling height is factored into the equation; each three-dimensional cubic square foot of space will require a certain amount of BTU usage to cool/heat accordingly. The smaller the volume, the fewer BTUs are required to cool or heat.

The following is a rough estimation of the cooling capacity a cooling system would need to effectively cool a room/house based only on the square footage of the room/house provided by EnergyStar.gov.

Area To Be Cooled (square feet)	Capacity Needed (BTUs per hour)
100 to 150	5,000
150 to 250	6,000
250 to 300	7,000
300 to 350	8,000
350 to 400	9,000
400 to 450	10,000
450 to 550	12,000
550 to 700	14,000
700 to 1,000	18,000
1,000 to 1,200	21,000
1,200 to 1,400	23,000
1,400 to 1,500	24,000
1,500 to 2,000	30,000
2,000 to 2,500	34,000

Insulation Condition

Thermal insulation is defined as the reduction of heat transfer between objects in thermal contact or in the range of radiative influence. The importance of insulation lies in its ability to lower BTU usage by managing as much as possible the inefficient wasting of it due to the entropic nature of heat – it tends to flow from warmer to cooler until there are no longer temperature differences.

Generally, newer homes have better insulating ability than older homes due to technological advances as well as a more strict building code. Owners of older homes with dated insulation that decide to upgrade will not only improve on the ability for the home to insulate (resulting in friendlier utility bills and warmer winters), but also have the value appreciation of their homes.