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HVAC Sizing Rules of Thumb

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The acronym HVAC stands for Heating/ Ventilating/ Air Conditioning. It's used to refer to such systems for homes and businesses. In these systems, air moves between the inside and outside of a home or other building. That means heat is continually lost or gained depending on the climate and weather conditions. To install the correctly sized furnace or air conditioning unit, designers must apply calculations that factor in the amount of heat gained or lost. Contractors occasionally use "rules of thumb" to size equipment for houses and businesses.

One rule of thumb estimates the average heat loss or gain based on the square footage of the structure. For example, the builder may decide that it takes 1 ton (12,000 BTU) of air conditioning for each 800 square feet of space. The problem is that climates, house size, season, number of windows and which direction they face, insulation, and the number of sunny days, to name a few conditions, all make a difference. A heating/AC unit that's too big not only wastes energy and costs more, it fails to maintain an even temperature, causes discomfort, and wreaks havoc on humidity levels.

Here are some things to consider when planning to install or replace heating and air conditioning:

  • Installing the correct size keeps costs down.
  • Correct humidity control prevents moisture damage from occurring.
  • Installing properly sized units costs less and will pay for itself in energy savings.
  • Cycling on and off is costly; if the furnace/air conditioner is sized correctly, it will maintain an even temperature.
  • Properly sized HVAC requires less ductwork, which means lower cost.
  • Correctly sized HVAC units help create a comfortable atmosphere for the building's inhabitants.

With fuel costs on the rise and environmental concerns at the forefront, it makes sense to go beyond rule of thumb guesswork and carefully calculate our HVAC needs. For more information on accurately measuring the heat load in your home, see our article on HVAC Sizing Calculations.

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