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Serving the Greater Grand Rapids Area | |
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Serving the Greater Grand Rapids Area | |
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Questions? Need Service? Click Here or Call: (616) 458-7304Sizing Your SystemOlder space conditioning systems (more than 10 years old) are often unreliable and much less efficient than a modern system. When it’s time for a new replacement, choosing one of the correct size (heating and/or cooling output) is critical to getting the best efficiency, comfort, and lowest maintenance and operating costs over the life of the new system. Some national surveys have determined that well over half of all HVAC contractors do not size heating and cooling systems correctly. The most common sizing mistake is in oversizing. This not only makes the new system more expensive to install, but also forces it to operate inefficiently, break down more often, and cost more to operate. Oversized heating equipment also often creates uncomfortable and large temperature swings in the house. Oversized air conditioners do not run long enough to dehumidify the air, which results in the “clammy” feeling and unhealthy mold growth in many air-conditioned houses. Incorrect Sizing MethodsIt is the installer/contractor’s job to perform the correct sizing calculation for the building. However, many installers only check the “nameplate” (the label on the unit that has the Btu per hour output among other things) of the existing system and sell you one just like it, or even worse, one that’s larger. This is a not a correct sizing method and not in your best interests! Other methods include simple “rules of thumb” based on the size of your home or using a chart that accounts for a variety of factors. While these methods might provide a first estimate, they should not be used to size your system. Why Most Older Systems are OversizedBefore the era of tightly constructed homes, it was not uncommon to install furnaces and air conditioners that had two to four times the necessary capacity. Since many people have added new windows, caulking, weather-stripping, and insulation to their homes, going by the nameplate is likely to result in an oversized system. Making improvements such as these to reduce heat loss in the winter and heat gain in the summer should allow you to install a smaller systems while still being comfortable, as well as saving large amounts of energy. Manual J and Manual D: The Correct Way to Size a SystemCorrect system sizing requires considering many factors other than simply reading the nameplate of the existing unit. Key factors for correctly sizing a heating and cooling system include the following:
Homeowners should insist that contractors use a correct sizing calculation before signing a contract. Manual J, “Residential Load Calculation,” published by the Air Conditioning Contractors of America (ACCA), is the recommended method for use in the United States. Steps a Good Contractor Should Take to Size Your SystemMany factors affect a home’s heating or cooling requirement, or “load.” A good estimator will measure walls, ceilings, floor space, and windows to determine the room volumes, and will assess the R-value of the home’s insulation, windows, and building materials. A close estimate of the building’s air leakage is also necessary. A blower door test is the best way to measure air leakage. When the contractors are finished, get a copy of their calculations, assumptions, and the computer printout or finished worksheet. This is your only proof that they did the job right. To summarize, when designing your new heating and air conditioning system, the contractor you choose should do the following:
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