BTU Calculations


Air conditioners and heaters the temperature of a given area by respectively removing or adding heat. The British thermal unit (BTU) is the measurement most commonly used to determine the amount of energy needed to change the climate in an enclosed area. The rating for a unit is typically expressed in BTUs per hour and there are several factors to consider when calculating which unit is best-suited for a given space.

Room Dimensions

  • The size of a room or a plurality of rooms is perhaps the single, most important factor to consider. A larger room will require a higher rating of heater or air conditioning unit to maintain a desired climate. This is due to the increased volume of air space. Higher walls also play a factor. The physical dimensions of the room or rooms may largely help dictate the energy needs, so every other consideration that follows will help lower the BTU per hour rating.

Room Insulation

  • Much like an insulated coffee mug, the insulation in a home dictates the energy needed to maintain a specified temperature for a room. The R-value of the insulation material in the walls is an indication of how well it can prevent the room from becoming warmer or cooler. A higher R-value corresponds with greater insulation capacity. Other factors that can lead into the insulation of the room from exterior heat sources include the flooring material and the R-value of the windows and doors.

Sunlight Exposure

  • The side effect of sunlight is the capacity to warm up rooms that you want to remain at a set temperature. A room that is in the path of direct sunlight exposure can lead to a higher BTU per hour rating for the air conditioning unit needed to sufficiently cool it. Sunlight can also work in favor of a heater, which can translate to less energy required to heat the given space. This factor can be minimized if the windows that let sunlight into the room have a high R-value.

Room to Cool or Heat

  • If the room you are trying to cool is a kitchen, it would follow that you would need to install an air conditioning unit with a higher BTU per hour rating necessary than in most other parts of the home. The amount of cooking with the range will help dictate the BTU per hour rating of heater needed for the colder months. This is the part of the home that experiences the most fluctuations as a result of using stove burners and ovens.

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