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Making Manual S “Super”

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ACCA’s Manual S: Residential Equipment Selection is under revision as part of the routine requirements set by the American National Standards Institute (ANSI).  ACCA saw this as the perfect opportunity to meet the growing desire to expand the use of renewable energy, a trend some call electrification.  Manual S has been a code requirement for five years.  As it continues to gain recognition and is implemented by more jurisdictions, this is the perfect time to make Manual S super.  

ACCA formed a working group to undertake the editorial review of the document. The Chair, Anthony Maynor, has a long history as an HVAC professional. Mr. Maynor stated, “I’m happy to have the opportunity to participate in the process. The working group comprises passionate specialists with the expressed desire to see Manual S continue the long tradition of clear, practical guidance for the HVAC system designer.” Anthony recently sold A. Maynor Heating & Air and has devoted himself full time to education and training. Bart James, President and CEO of ACCA, said, “We are very fortunate to have a recognized professional and industry leader steering the work on one of the cornerstone manuals in ACCA’s design process.” Maynor is joined by: 

  • Phil Forner, President of Allendale Heating Company, former Chairman of the Board, and winner of ACCA’s prestigious Spirit of Independence award. 
  • Alex Meaney, MiTek Industries, Wrightsoft Senior Trainer.  
  • Kimberly Llewellyn, Mitsubishi ElectricPerformance Construction Technical Lead.       

Mandatory Language 

ACCA design manuals have begun a fundamental change in their structure. In the past, the manuals were written in very informal, easy-to-understand language. When the manuals were recognized as ANSI standards and code requirements, they transitioned from informative language that used terms like may and should into mandatory language that used terms like must and shall. To further improve the manuals, the mandatory requirements were consolidated in the opening normative sections, and the useful discussion and examples were consolidated in the informative section. 

As the working group looked at the current normative section, it noticed opportunities to further refine and streamline the minimum requirements. Maynor cautioned, “We are working very carefully to ensure the manual retains clear, consistent guidance. We want to make it as simple as possible, while we hold onto all of the fundamental provisions that support good HVAC system design.” He further noted, “Clear mandatory language also supports code officials who want to support enforcement of right sized equipment.” 

Heat Pump Sizing tolerances 

One element that is garnering a great deal of discussion is sizing tolerance for heat pumps. Maynor said, “We recognize the strong desire to use renewable energy and want to ensure Manual S provides pragmatic support for this effort. To that end, the working group has reached consensus on the following issues: 

  • Dwellings in dry climates (those with a Manual J Sensible Heat Ratio of 95% or greater) or those that use ancillary dehumidification to control latent cooling loads will be able to use expanded sizing tolerances.   
  • Removal of the requirement to consider the ratio of heating degree days (HDD) to cooling degree days (CDD). It is understood that consideration of the HDD:CDD ratio was the first step toward opening this requirement to support expanded sizing tolerances in cold climates. However, with the provision for a dry dwelling, this was no longer deemed necessary. 
  • Heat pump sizing for heating mode is a topic the working group would like to create. This will require special equipment, either two-stage or variable capacity equipment, and ancillary dehumidification to ensure latent cooling loads.   


Jon Winkler and others at the National Renewable Energy Laboratory published an excellent white paper on the process to calculate residential dehumidifier loads. This white paper was influential in the dehumidifier sizing guidance contained ACCA’s Manual for Low Load Home (Manual LLH).   

The working group continues to discuss this part of the standard and has held conversations with manufacturers and industry experts like Joe Lstiburek. Maynor noted, “Humidity control is a vital part of HVAC system design. This is true not only for humid climates, but for lowload homes that retain moisture from cleaning, bathing, and what occupants produce.”   


Maynor noted that the working group hopes to conclude their revisions by the end of the year. At that point, an extensive review committee will be formed to assess the edited draft for technical accuracy and practical usage. The committee will consist of HVAC business owners, equipment manufacturers, energy efficiency experts, utilities, and allied associations. Upon approval by the review committee, the document will be processed through the ACCA Standards Task Team to ensure all ANSI requirements have been met at this point in the standard’s development. It will then be submitted to ANSI for a 45-day public review where all interested parties are welcome to provide comments.  

Rob Minnick, Chair of ACCA’s Products Committee, noted, “ACCA has been the leader in HVAC system design due to the hard work of Hank Rutkowski, PE. We owe him a great deal and want to ensure we produce a standard that continues the tradition of excellence.”
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