Manuals J and Manual D: Together, They're the Cornerstone of a Quality A/C Installation

If, as the old saying goes, "rules were made to be broken," nowhere does this seem more applicable than in using Manual J and Manual D calculations when installing home HVAC systems. According to the 2012 IRC (International Residential Code), adopted by most local building department authorities as law, Manual J and Manual D calculations must be followed in the installation of all home HVAC systems. Even though legally required, these regulations are often not followed, to the detriment of affected homeowners.

Manual J, published by the Air Conditioning Contractors of America, uses a worksheet to determine proper sizing of HVAC equipment for specific applications. Factors used for the calculations include:

  • Climate
  • Size, shape and layout of the residence
  • Amount of insulation present
  • Rate of air leakage
  • Window sizes, orientation and glazing materials
  • Heat loss and heat gain under worst-case conditions

For new construction, Manual D is utilized by incorporating calculations derived through the Manual J process to determine correct sizing and configuration of air duct systems. Use of Manual D is also required by the IRC.

It's been estimated that more than half of the HVAC installations in the U.S. are not done in compliance with Manual J and Manual D calculations but through the "rule-of-thumb" method. While the Code provides a loophole for using Manual J by allowing for, "other approved heating and cooling calculation methodologies," the rule-of-thumb method is not approved, even though it continues to be the method most often used. An example of this would be "one ton of cooling for every 400 sq. ft. of interior floor area."

Most A/C installations are known to use oversized equipment, in lieu of properly sizing units according to precise calculations provided by Manual J. These systems are more expensive to buy and operate, provide substandard air comfort conditions and allow for high humidity in your home's interior air.

Thermacon Service Company, Inc., has been serving our clients in the Golden Triangle area of Texas for 30-plus years, using Manual J and Manual D to precisely size our HVAC installations. Please contact us for information/advice on any of your home air comfort/quality needs.


R-22 Refrigerant Supplies Are Getting Shorter--Have You Started Thinking About an A/C Replacement?

No one likes to be rushed when it comes to making a big-ticket purchase like a central air conditioner. But R-22 refrigerant supplies are waning, which means that it really is in your best interest to start thinking about replacing your A/C system.

As you may know, the U.S. Environmental Protection Agency is phasing out R-22 because of its ozone-depleting qualities. About 80 percent of the A/C systems in the United States depend on this refrigerant, which offers some good news and not-so-good news at the same time: You're far from alone in facing the prospect of replacing your A/C system, but you’re also going to be competing for R-22 to keep your current air conditioner running. Also consider:

  • As the phaseout of R-22 continues, prices have risen dramatically, and they are expected to continue moving in this direction. Homeowners in some parts of the country are understandably alarmed, but they tend to overlook the fact that R-22 is a greenhouse gas that is harmful to the environment. Replacing your air conditioner  with a system that uses the new refrigerant, known as Puron, is safer.
  • A new Energy Star-approved air conditioner will operate at 90 percent efficiency or more, and you’ll benefit by paying less to run it. Even if your system is less than 15 years old, the U.S. Department of Energy estimates that a new system will save you between 20 and 40 percent on your utility bills.
  • The U.S. government is trying to take the sting out of air conditioner replacement by offering a tax credit. Specifically, the 25C residential energy tax credit allows eligible homeowners to claim up to 10 percent of the cost of a new central air conditioning system, up to $300.

As the advantages add up, call the experts at Thermacon Service Company for an evaluation of your current system and let us show you how you can stop sweating the dwindling R-22 refrigerant supplies.