Manual J

Manual J

Bigger is not always better!

Did you know that there is a protocol to follow when determining the size of your HVAC system? Developed by engineers in the heating and air conditioning industry and adopted by Air Conditioning Contractors of America (ACCA), Manual J has become the standard for ensuring the selection of accurately sized heating and air-conditioning equipment thru heat and cooling load calculations. This process not only ensures compliance with building codes but it also creates efficiency for homeowners.

There are three main reasons why it is important to select the correct HVAC system:

Efficiency: Resources are scarce and energy consumption can be very expensive. Purchasing an HVAC unit that is larger than needed is more expensive to operate for multiple reasons. With oversized units, the space will be cooled faster causing the system to turn on and off continuously, also known as short-cycling. Short-cycling will damage the air conditioning unit causing unnecessary wear and tear. Also, these units consume the most amount of power when the compress is first turning on and to achieve efficiency it needs to be running for at least 10 minutes or more prior to shutting down again.

Comfort: When air conditioning units are larger in size than what’s needed, the system will quickly cool down the air in the home, triggering the thermostat to its desired temperature causing it to shut off the system quickly and without allowing the proper time needed for condensation (typically 10 minutes is what’s needed), which is the process of cooling down the air conditioning coils to dehumidify the air in the home.

Air Quality: With a larger air conditioning unit than needed, the humidity was not able to correctly be removed causing too much moisture within the air. This humidity in the air typically causes mold or mildew in low air flow areas and bad odor within the space.

How do you prevent from having an oversized air conditioning unit installed? Here is how:

During an ACCA approved Manual J load calculation, Rapid Duct Testing’s team of licensed professionals will not only provide the heating and cooling load for the entire space, also known as a block load, but a calculation based on each room known as a Room-by-Room calculation. In designing heating and cooling for a residential home, it is important to consider how the heating and cooling will be distributed throughout the entire home in proportion to each room and its specs.

In a complete load calculation, not only are the apparent areas such as the orientation of all walls, ceilings, floors, appliances and glass considered by our team, but also the building materials that were used during the construction of the home such as roofing and windows. These calculations are then combined with the load calculations of other components of the home like piping and ducts to determine the total load and in turn the correct size air conditioning unit needed for the space in question.