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Before Investing in a Pricy HVAC Upgrade, Ensure Load Calculations Are on Tap

Installing the correctly-sized system to heat and cool your home requires careful attention to load calculations provided by correctly using Manual J and Manual D. Consequently, oversized installations are very common. Manual J focuses on cooling load calculations, while Manual D properly matches ductwork to the blower fan.

Here’s why you can save money and avoid unnecessary maintenance when you hire a contractor who uses these industry standards:

  • Using rules of thumb for A/C installations means you’re just guessing. As building codes become more stringent, old rules of thumb no longer work because homes have become more efficient over time. Especially for new homes, their cooling load has gradually decreased.
  • Professionals complete an inspection of your home and ask questions to find the right numbers for using Manual J. They know that the more information they have, the more accurate the load calculation will be.
  • If any important numbers are missing or don’t seem right, contractors may complete tests using a door blower and other equipment.
  • Industry-specific software is available to assist with using Manual J, and good contractors use it. They also have an excellent understanding of HVAC design principles. If Manual J calculations aren’t right, Manual D calculations won’t be right either.
  • System components must match correctly for best efficiency and longer operational life. For example, change the blower fan without changing the compressor, and you’ll need new load calculations.
  • Contractors who purposefully overestimate the size of your new A/C to make sure it cools as much as possible under any circumstance aren’t helping you in the long-term. An A/C that’s too large cycles off and on much more than it needs to. It costs more to operate, requires more maintenance and causes more indoor humidity.
  • The design of your home, landscaping, quality of construction and activities of the occupants affect load calculations. To get the most out of an HVAC upgrade, make sure your contractor thoroughly inspects your property and uses professional references such as Manual J and Manual D.

For more information about why load calculations make such an impact or for answers to any of your other home comfort questions, contact HVAC Unlimited. We proudly serve northern Virginia homeowners in and around Fairfax, Alexandria, Springfield, Arlington, Centreville, Reston, Burke, Lorton and Ashburn.

Get the value-focused & trustworthy service you deserve today!
  • For emergency service, please call our office at 703-493-1200.


We have staff on call 24/7 to provide assistance to our customers. We provide emergency service up to 8pm for all customers and 24/7 for contract customers. For quick, efficient emergency services, please call (703) 493-1200 immediately.