Monthly Archives: February 2013

Load Calculation – Step One to New HVAC

Whether you are replacing an old furnace or air conditioning system or purchasing one for new construction, obtaining an accurate home heating and air load calculation is important in selecting the right units for your house. Properly sizing systems to match your home’s heating and cooling needs affect the efficiency of the components as well as indoor comfort levels. Traditionally, many HVAC contractors based recommendations for systems on the total square footage. Beginning in 2010, however United States building codes require contractors to size systems as determined by actual heating and cooling load for each building.

Although some contractors still recommend home heating and air conditioning systems based on square footage, Keith Air Conditioning, Inc. in Mobile AL, performs load calculations whenever the company quotes installations for new furnaces and air conditioning systems, so customers don’t have to worry whether they are receiving the right components for their homes. The consequences of a wrongly sized system can be severe. Units can operate loudly, fail to keep people comfortable or maintain proper moisture control, cycle on and off frequently, resulting in higher energy bills or a break down of components.

Determining your home’s heating and cooling load depends on variables such as local climate, house size, how the building lies in relation to the sun, U-value of windows and tightness of the building envelope. Manual J calculations, as recommended by the Air Conditioning Contractors Association of America (ACCA), are most commonly used by contractors to size home heating and air conditioning systems. This method analyzes all thermal characteristics of every wall, floor, ceiling, door, and window while also taking into consideration aforementioned factors and other items that can affect indoor comfort such as duct leakage, lights and home appliances. Manual J even calculates the amount of each heat and humidity an individual will produce in a building.

Whole house Manual J load calculations are the ones most commonly performed. However, if an inspection of your home shows that you need duct repair, modification of current ductwork, new ducts or need HVAC for an addition, you will also need a room-by-room calculation that determines heating and cooling needed for each area. Room-by-room numbers also help determine duct sizing and layout.

Once Manual J calculations have been performed, our technicians will have the information necessary to accurately select the proper furnace or air conditioning equipment based on performance traits such as the unit’s capacity to remove heat and moisture from the air, or in the case of a furnace, its ability to provide heat. The unit’s ability to move air and at what pressure is also taken into consideration.

These factors are important because two systems of the same size can operate much differently. If indicated, our technicians will also perform Manual D duct calculations to determine proper airflow. Our customers can rest assured that Keith Air Conditioning, Inc. in Mobile AL will properly size and recommend the best HVAC system for your home.