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!

New Technician License for North Carolina Plumbing, Heating, and Fuel Piping.

“This Technician license is not a contractor license, and is limited to supervision of work within the technician’s qualification(s).” It is intended to provide relief to contractors who have multiple jobs over a large area.

So why should I be care about this new license as I want my contractor’s license?

“At any time after passing the technician license, the technician license may be upgraded to a contractor license by applying and passing the business and law examination.

This is huge for a couple of reasons. The bus/law exam is 50 questions in 60 minutes. The questions are not hard but the time limit makes this a tough exam. Most of my students report back that this test is frustrating. Why not take the technician exam and then go back later and take the business exam?

For people who are having problems getting their Plumbing or Mechanical License.

Sign up for both the technician exam and NCCTI Contractor Exam Prep Class. Your first exam will be your easiest. Preparation and practice is the key. Take a look at our Free Demo class. Continue reading

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.

Warning, some memorizination required!

“Change Four” and the National Electric Code


I constantly preach the importance of look up speeds as a core skill for student success. After all, it’s an open book exam.

Some memorization definitely helps and “Change Four” is one of them.

Larger than 6 AWG

For Conductor Identification


What is the next larger conductor larger than 6 AWG?


No. 4 AWG.

Notice that the rules change. This rule also applies to the “grounded conductor”.

NEC and the “Change 4” rule

There are two more “Change 4” NEC code references. Can you name them?


Memorizing “Change 4” just might lead to 3 or more correct exam answers!

Life is good!