When competing with the 100 degree heat, it’s natural to have a jaw-dropping reaction to your first electric bill of the summer. Sure, maybe the electric bill goes up the same amount every summer, but that still doesn’t dull the shock you experience year-after-year when you see the balance due at the bottom of that paper. Having an HVAC system that’s too large for your home can also increase your electric bill exponentially. When it comes to HVAC systems, the “bigger is better” principle is replaced with the “less is more” principle.
Having an HVAC unit that is too large for your home will certainly cool it quickly, but will also suck the moisture out of the air, leaving it very dry. Similarly, an HVAC unit that is too small for your home will take forever to cool it, running up an out-of-this-world electric bill in the meantime. Determining the properly-sized HVAC system for your home is not only crucial for maximum comfort, but also maximum bang for your buck.
Making a Rough Calculation
There are two ways to estimate HVAC usage. Three, if you decide to simply let a professional do it. While consulting a professional is certainly a recommended step as many factors play into determining HVAC usage (number of windows, insulation, ductwork, climate type, home layout, etc.), you can get a head start by calculating this yourself. The first step is to find out/calculate the square footage of your home. Many homeowners know this from their realtors when they initially purchased the house, but those who don’t will need to multiply the length of each room by the width and add it all together.
Once this has been determined, you can multiply that amount by 25BTU to get a rough estimate of how many BTUs your air conditioner will need to be. When you hire a professional to install the A/C unit, they will still make their own calculations, but you can at least use yours to assess the approximate size of the A/C unit you need and about how much it will cost.
Calculating Heat Load
The second way to determine HVAC usage and size is to calculate the heat load. Heat load refers to the amount of cooling or heating that is required to get your home to its desired temperature. The first step is to once again determine the square footage of your home. From there, multiply that by your home’s average ceiling height. Add another multiplier for the difference in temperature desired and the temperature outside (i.e. if it is 30 degrees outside and you would like to keep your home at 70, this number would be 40). The final multiplier should be .135, which represents the fact that the unit is for a sealed structure. In other words, there are no parts of your home that are permanently exposed to the open air.
To put this into perspective, imagine you have a 3000 square foot home with 8-foot ceilings and you are trying to keep it at 70 degrees in 30 degree weather. You would then calculate 3000 x 8 x 40 x .135. This equates to 129,600 BTUs.
Other Factors to Consider
Installing a properly-sized HVAC system is not only beneficial for comfort and reduced energy bills. The US Department of Energy estimates that most homes currently have an oversized HVAC system and would benefit from re-sizing. This means that a large portion of homes are using more energy than necessary to keep the space cool, making this a serious environmental concern as well. On the other hand, as homes in general have gotten larger over the years (from 1,645 square feet on average in 1975 to 2,434 square feet today), many HVAC systems have been forgotten in the remodeling process and may also be too small for their corresponding structures. Overall, HVAC systems across the country are in need of re-evaluation, except possibly those in newly-constructed homes.
Adequately-sized ductwork is also an important consideration, as it aids in proper circulation and contributes to increased insulation and decreased leakage. With effective ductwork, a smaller HVAC system can work for a larger space as it does not have to account for hot/cold air from the outside seeping through cracks, windows, attics, etc. Using this knowledge, you may want to take a second look at the HVAC system you currently have in place. This will allow you to conclude if it’s really the summer heat that’s responsible for your home’s uncomfortable temperature, or if it’s simply a case of an improperly sized HVAC system.
Ellie Batchiyska is a writer for Plumber’s Stock, a leading online retailer for plumbing/HVAC supplies and parts.