Posted on: December 2, 2019 Posted by: Caitlin Comments: 0

Installing a new HVAC system in your house is an important step for any homeowner. The cost of replacing or installing an HVAC system during construction or renovation is one that many homeowners will experience. As a homeowner, it is essential to know the correct size for your HVAC system.

The Importance of HVAC Size


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HVAC size is important for many reasons. One of the main reasons is how it handles your home’s humidity levels. HVAC systems that are too large have short cycles and cannot effectively regulate your home’s humidity levels. Systems that are too small will struggle to remove moisture, even if the air cycles are longer. Humidity control is important to controlling biological growths such as mold, mildew, and dust mites.

Correctly sized HVAC units will also maintain consistent temperatures. Shorter cycles of large HVAC units lead to poor air circulation, creating hot and cold air pockets. Units that are too small cannot meet the energy demands of the thermostat, leading to poor airflow in the house. Larger HVAC systems will consume more energy due to frequent stops and starts. Smaller units have longer cycles that use more energy and reduce efficiency.

Calculating the Best Size

To determine the appropriate size for your HVAC system, you use two calculations.

First, find the floor space square footage in your home. You might have the information with your homeownership papers or you might need to measure in yourself. To measure your home’s square footage, use a tape measure to measure each room’s length and width. Multiply length and width to get the total area for that room. Record measurements for each room and hallway, then add all the measurements together.

Next, you’ll need to find how strong of a system you need. You can use a measurement called the British Thermal Unit, or BTU, to measure energy for heating and cooling your home. A base energy amount is approximately 25 BTUs. To know the BTUs your house requires, you multiply the number of square feet from your previous calculations by 25. However, if you have high ceilings of 8 feet or taller, it’s necessary to multiply this final calculation by 1.25, or 25%.

The Professional Method: Manual J

The calculations that you’ve made do not take into account other important factors, such as the climate of the area where you live, window placement, the number of windows, the depth of home insulation, the number of people who live in the house, and lighting placement. Trained HVAC professionals will use what is called Manual J calculations, which will provide a more accurate assessment. Manual J uses such calculations as:

  • The actual orientation of the house to measure solar heat gain.
  • Insulation values of insulation and the building materials.
  • Curtains, drapes, and blinds that can change the house temperature.
  • The number of bedrooms your home has, plus one.

If you have questions about the right size for your HVAC system, contact J&J Mechanical Inc. to have an HVAC professional help you decide the best size of HVAC system for your home. Installing an HVAC system in your home is costly, so make sure you do it right the first time with help from professionals.

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