ACCA MJ-8 and Window Heat Gain Calculations

Fenestration Cooling Load

There is a big difference between calculating heat gain for generic windows and advanced calculations when windows are rated by the National Fenestration Rating Council

For Generic windows

Tables 3A-1 (vertical glass) and 3C-1 (skylights) are used to locate the HTM.

Looking at Table 3A on page 289 we find all of the needed formulas. Table 3A-1 – Clear Glass is fairly straight forward. To find the HTM, the CTD must be calculated and the exposure known

Just make sure you understand that a Triple Pane window assembly has the same value as a Double Pane Low-e window assembly.

Now let’s look at Table 3D

It’s a whole new ball game, no wonder MJ-8 recommends using software to calculate the window loads. Using this method let’s look at page 303, Table 3D, Default Cooling HTM for NFRC Rated Fenestration Windows, Glass Doors and Skylights. Calculating the fenestration heat gains will require different formulas and more Tables to find formula values such as PSF and CLF (Table 3D).


When you enroll in one of our Heating Exam Prep course, our Tutorials will break down the dreaded ACCA Manuals into simple, straightforward lessons that will help you pass your contractor exam on the first attempt.

Heating Load Calculation for a Concrete Slab on Grade Floor, ACCA Manual J-8


If on Heating Contractor Exam you get a heat load question regarding a structure that has a slab on grade, make sure you understand a few differences. First, the areas (sq.ft) of opaque panels are not used in the heat load calculations. Look at pg. 435, ground slab load calculations are based on F-values. F-values are simply the heat loss per foot of exposed edge.  You use a linear measurement, not a square foot measurement that is used on every other opaque heat load calculation.


Heating Load = HTM x Running Feet of Exposed Edge

So, if you receive a question – What is the heat gain for a slab on grade? Take the gift!  There is no reason to dread heat load questions, only educated. NCCTI can help, our ACCA Tutorials that are included in NC Heating Exam Prep Courses, will make learning easy. Sign up now.

ACCA Manual D vs. the 2012 NC Mechanical Code

ACCA Manual D does not endorse the panning of joists.

Too many air leaks and a rough surface that causes air turbulence. But, if you look in Chapter 6, Duct Systems in the 2012 Mechanical Code, panned joists are allowed for return air.
Take a look at Section 603.18 on page 61, Return-air intake. Notice that the Fpm value for return air grilles shall not exceed 450 Fpm. Get your Manual D out and turn to Appendix 1. What is the maximum Fpm value for return air grilles?

The last piece of the puzzle can be found on pg. 51, Section 603.2 Duct sizing. “Ducts installed within a single dwelling unit shall be sized in accordance with ACCA Manual D or other approved methods.” Approved methods mean it is the AHJ’s call. If your building Inspector allows it, then it is legal.

For your Heating Exam

One of the key skills required for passing the exam is quickly deciding which reference book the exam question is asking for. Is the question referencing Manual D or the Mechanical Code? To develop this key skill, enroll now? We have solutions to your problems!

Will the real ACCA Manual J Please stand up!

When preparing for the North Carolina Heating Contractor Exams, make sure you purchase the correct MJ-8 Exam book. The correct ACCA  Manual J-8 is Manual J Residential Load Calculation 8th Edition – Full, Version 2.1. This is the Manual you will be handed when you take your Heating Exam. Do not buy the abridged version.
North Carolina Board of Examiners – Book Reference List
Their reference list just lists Manual J-8 as the needed reference (on their website). If you call, Manual J8, Version 2.10- Full Version will be their answer. Why not cut the chase and just list the correct version on their Book Reference List? For the old timers like me who has the MJ-8 Version 1 book, toss it in the trash and buy the correct one!
Where can I buy the Version 2.10 book?
You can always buy this book from and then go to the ACCA Store. You might try or you can just Google ACCA Manual J-8 and investigate what pops up.
The ACCA Manual J-8, Version 2.10 is a better version. This Manual is matched to ACCA’s Manual N, Edition 5. Learn the new Manual J-8 and you will be half-way home on understanding Manual N.

NCCTI’s mission is to train Heating Professionals the basic fundamentals needed to pass North Carolina Contractor Exams.

North Carolina Energy Code Made Simple

North Carolina Energy Code Made Simple

I recommend memorizing a few things:

  • Chapter 4 – Residential Energy Efficiency
  • Chapter 5 – Commercial Energy Efficiency
  • Use the Table of Contents to look up questions

Define Fenestration, Thermostat Dead Band, Economizers, and COP

Now answer the following question, “What is the difference between the residential and commercial requirements regarding air intake and exhaust damper requirements?”

Hint – look at 403.5 and 502.4.4

Don’t forget

  • Ductwork and pipe insulation requirements
  • Time clock controls
  • Minimum efficiency requirements
  • Sign up for NCCTI’s practice exams

Heating Group 3 Contractor Exams and Manual Q Questions

Heating Group 3 and ACCA  Manual Q

Now that Manual Q is included on H-3 Class I exams, it would be in your best interest to become familiar with the Appendices of ACCA Manual Q.

First, let’s look at Appendix 7 HVAC Duct Design Symbols.

This section has a full page of HVAC Symbols that have been on past Heating Contractor Exams.  Symbols have been on past exams when Manual Q was not be listed as a reference book. Kind of tricky!

ACCA manuals are written by an engineer for engineers.

Reading and understanding ACCA Manuals is a tough pill to swallow. Unfortunately, it’s part of the reference material on the exams. No sense in whining about the ACCA Manuals, this is their game and we have to play by their rules. As there only going to be a few questions from Q on the H-3 exams, I would not put a whole lot of time studying Manual Q. But I would pay attention some to Section 3 and Section 10. Please understand that any section or part of Manual Q is fare game but our goal is to achieve a passing grade and still have a “life”.

Become familiar with Appendix 1 Equations, Appendix 2 Friction Charts, Appendix 3 Charts and design data, and Appendix 7 HVAC Symbols. Some of the Appendices in Manual Q are similar to Manual D, just make sure you keep in mind that Manual D is residential and Manual Q is commercial.

Manual Q and Elevation and Temperature Corrections

On page 3-6, Manual Q, states that” Elevation and temperature corrections are always required when the elevation exceeds 2,000 ft. Now, turn to Appendix 3, Figure A3-4, and at the bottom of page – notes. “Altitude correction not required below 1,500ft.” Read each exam question carefully! Work on increasing look – up speeds.

Sizing Fuel Gas Lines

402.4.1 Longest Length Method for the Fuel Gas Code

Plumbing, Heating, and Fuel Gas Contractor Exams contain questions on fuel gas pipe sizing. It would behoove applicants to make sure they are comfortable sizing gas lines using the Fuel Gas Tables and Longest Length Method.


Maximum pipe length must be calculated first.

Add up the maximum gas demand, choose the correct Table that matches the fuel being used, and calculate the maximum pipe length from the point of delivery to the farthest outlet. The next step is to choose the correct row in the Table that is equal to or greater than the calculated length. All pipe system values will be taken from this row.


For Contractor exams, use the Longest Length Method.

For residential and light commercial systems, the Longest Length Method is the preferred method. In reality, this method oversize the gas pipe somewhat and would not be a good choice for a large commercial system. The installation cost would come into play.


NCCTI provides a free online Tutorial that will help the student understand the Longest Length Method.

Free Mechanical Contractor Exam Question

Understanding Contractor Exams 101

Do not bring what you do in real life into the exam! I would argue that a person with no Mechanical Contracting experience would fare better on Heating Contractor Exams than an experienced person.

The Board of Examiners Contractor Exams is based Code books and Code is based on the minimum. What this means, if you are a conscientious contractor, then you are doing more than the minimum. You could build a whole house to code and the house could be a piece of junk.


2009 NC Mechanical Code, Section 307.2.3 Auxiliary and secondary drain systems

Look on page19 and read the last sentence in the first paragraph, “One of the following methods shall be used.” Following this paragraph, you have four options to satisfy this code section. I had a student that was taking the H-3 Heating Exam and was asked a question about this section. Instead of reading the appropriate code section word for word and not adding anything to it, he used his experience.


Let’s say we are installing AC equipment in an attic. We use option No. 2 and install a separate overflow drain that connects to drain pan and discharges to a conspicuous place. A smart installer would install a water level detection device too. Why not have some extra insurance against ceiling damage? It’s just makes good business sense! But, it makes bad exam sense.


Derive your answer from reading the code.

The key to success is to read and understand the Exam Question. Read all of the answers. Pick the correct reference book and look up the question in an efficient manner. It takes practice to hone this skill. NCCTI offers Contractor Practice Exams and subject matter Tutorials to serve the Contractor Community. Why wait, sign up now!