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FAQ’s – Builders

Why do I need a Manual J?

It is similar to calculating the lumber needed for a specific building project: you don’t want to run short or purchase more than you need. ACCA Manual J is your calculation for the amount of Btuh’s (heat) required to be removed from or added to your home in order to maintain comfort.  Any other method is guessing. It’s also required by the 2009-2015 International Residential Code. Not having one can also lead to issues caused by over sizing equipment, such as high utility costs and/or humidity levels.

Doesn’t my contractor already do their own calculations?

Not all contractors run ACCA Manual J load calculations; they still rely on mystical “rules of thumb” and/or “their years of experience.”  While some contractors do run their own load calculations, they are often inaccurate due to not understanding the building science behind HVAC design. Rules of thumb should never be the basis for a final decision, and years of experience work well when you are applying what you’ve learned from the mistakes you’ve made. Many HVAC contractors wear multiple hats: selling, ordering materials and installing systems, etc. Accurately designing HVAC systems is time consuming and can be seen as an unnecessary burden.

As a third party provider of HVAC design services, we only focus on providing accurate load calculations using the most current industry standards.  We also incorporate our combined 65 years of HVAC design and installation, as well as building science experience to ensure your homes are designed correctly.

What is the difference between ACCA Manual J and Manual S?

Manual J is the process used to determine the amount of Btuh’s (heat) required to be removed from or added to your home in order to maintain comfort.  Manual S is the process used to select the appropriate equipment based on the equipment manufacturer’s performance data. This ensures the equipment is capable of delivering the Btuh’s determined by the Manual J calculation.

Who is responsible if the system does not cool adequately?

If the system fails to cool or heat after being installed per our design, then Enerlogic is responsible.  Our calculations are only as accurate as the information you provided to us.  With that said, your HVAC contractor must ensure their air distribution system complies with the duct configurations we used in the load calculations. They are provided with the Manual J report.  Over designing or an inefficient design can increase the load just as much as using the wrong window or insulation values.

I’ve provided a duct layout for permitting, but the City has rejected my permit because I did not have a Manual D, what is that?

A duct layout is just that, a diagram of how the system is proposed to be installed.  ACCA Manual D is the third procedure used to formulate the systems duct sizing. We use the information from your ACCA Manual J & S and the equipment manufacturer’s expanded blower performance data to determine the proper duct size. The Manual D also includes important information the technician will need to properly commission the system and includes the design room to room cfm for air balancing.  Finally, the information from the Manual D will be used with the ACCA Manual T grill sizing procedure to insure the air will be properly distributed within a space as designed.

Do I just need the Manual J to give to my contractor?

Yes, all of the ACCA Manual J load calculations we perform also include the Manual S. This is used to inform the contractor of which system is to be used and will match the Manual J calculations.

However, there are several reasons to also have us provide the Manual D and duct design. They include:

  • assured comfort and efficiency,
  • reduced confusion when using multiple contractors,
  • reduced warranty cost,
  • increased home owner satisfaction, and
  • the 2015 International Residential Code requires ACCA Manual D to be completed on all homes started after September 1, 2016

At Enerlogic we would be happy to answer all of your HVAC System design questions and provide you with design services in a timely manner.

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