The load calculation that HVAC professionals conduct before installing a new heating and cooling system provides critical information about its sizing. In order to operate most efficiently and keep the home comfortable, all HVAC systems must match the conditioning load the home requires.
The industry uses software called Manual J to determine the size of systems. The inputs include detailed data about the home’s overall energy efficiency, including:
- Its insulation levels.
- Number of windows, their positions, size and orientation to the sun.
- Rates of air leakage through the envelope.
- Total cubic footage to condition.
- Heat-producing appliances indoors.
- Layout of the home.
- Number of residents and their ages.
- Preferred indoor temperatures.
- Landscaping factors.
The HVAC pro goes through the home on a room-by-room basis and inputs the details of each space. When finished, the software returns a recommended size for the new equipment.
The load calculation is critical for the process because oversized or undersized systems will:
- Use more energy.
- Reduce indoor comfort.
- Break down faster.
Of the two, it’s better to install an undersized system than oversized. Equipment that’s too large run in short cycles, which means they turn off quickly, and leave rooms further from the air handler uncomfortable. In the cooling mode, the system
won't remove as much humidity.
Since a new HVAC system is a big investment, it’s important to take the time and effort to conduct the load calculation at the start of the replacement process. As a result of working through the details, you may find you
use landscaping to lower the conditioning load, or make energy improvements that would cut the size of system you need.
Adding insulation and
sealing air leaks are both affordable projects that cut the conditioning load indoors. You’ll save money from the start, since smaller systems cost less. Over the long term, your energy bills will be lower, as well, and you’ll experience fewer repairs.
When you’re choosing a new HVAC system, insist that your contractor performs the load calculation. To learn more, contact
Russell’s Heating & Cooling, providing HVAC services for Hampton Roads-area homeowners.
Our goal is to help educate our customers in Chesapeake, Virginia and surrounding areas about energy and home comfort issues (specific to HVAC systems). For more information about load calculations and other HVAC topics, download our free Home Comfort Guide or call us at 757-750-1831.
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