Manual J Calculations

Tekneca Manual J – Load Calculation Services

Having the correctly sized heating and cooling system in your home starts with the calculating of the homes required heating and cooling loads.  ACCA’s Manual J is the first step in the HVAC calculation and in ACCA’s System Design Process.  ACCA Manual J is the most proven industry standard for calculating and sizing residential HVAC equipment and systems.  Performing the Manual J calculations, you are able to accurately determine the total amount of heating and cooling needs of the home.  The load calculation accounts for the sources of heat gain and heat loss and these sources are what we call loads.

The Manual J process calculates how much heat energy and at what rate you have to add or remove to provide the acceptable level of comfort for the occupants.  With Manual J you are calculating how much heat a house loses (heat loss) in the winter and how much heat it absorbs (heat gain) in the summer.  It is an account of the total heat flow into and out of a home, depending on the time of year.

Thus, Manual J is calculating the heating and cooling requirements.  These heating and cooling requirements are also known as the house loads.  This tells you how much heating capacity (from the heat load) and how much cooling capacity (from the cooling load) is required.  With these Heat Load and Cooling Load requirements, you can now size and select the equipment to match your house.  Without proper sizing of equipment, you can experience a variety of issues including higher energy bills, uneven heating and cooling, ineffective air flow and lower levels of comfort.

There is much involved in completing an HVAC design, but the Manual J process is the first step in the calculation requirements, providing you with the proper heating and cooling loads.  These loads can now be used to move on in the HVAC design process (if required) with the Manual S equipment selection and the Manual D duct design.  Manual J calculates requirements, Manual S selects the appropriate equipment and Manual D designs to deliver the air conditioning and heating throughout the house.

ANSI Manual J Cover
Sample Manual J Report
Sample Manual J Report

Benefits of Calculating using ACCA’s System Design Process

ACCA’s System Design Process includes Manual J, S, D.  Whether your project requires just Manual J or the complete system design process, there are many benefits to using all or just part of this system.  Your maximum benefit is achieved through performing the complete process as this involves covering all aspects of HVAC calculations and design.

The ACCA’s manuals are the only procedure recognized by the American National Standards Institute (ANSI) and specifically required by residential building codes.  Methods not based on actual construction details, nor founded on relevant physical laws and engineering principles, are unlikely to result in correct equipment sizing maximum efficiency and comfort.

Efficiency / Economic

Whether we are talking about just a heating system, or just a cooling system, or a complete system, an improper sized HVAC System will cost you more money to operate.  Additional costs arise from overpaying for oversized equipment and paying for higher operating costs.  Oversized equipment will result in short cycling, causing inefficiencies and additional wear and tear on the equipment.  Undersized systems create issues as well, as the HVAC system will run continuously.  A properly sized HVAC System will give you the optimum efficiency and operate with reduced costs including reduced energy usage.

Occupant Comfort

Improved occupant’s everyday comfort and satisfaction
Smaller temperature differences between each room
Reduced noise levels

Indoor Air Quality

Ensures Indoor Air Quality
Reduced allergic reactions & respiratory problems
Decrease in potential for mold growth
Improved humidity control

Equipment Related

Higher HVAC equipment efficiency, system is matched to home
Properly sized ductwork, which deliver the optimal amount of air to each room
Longer equipment life

Health Related

Less potential for mold growth
Improved environment for health issues such as respiratory conditions

Manual J – Load Calculation Factors

The HVAC load calculations utilize a number of factors to determine the energy needs of the home.  It is important to accurately calculate these to prevent oversizing or under-sizing of HVAC equipment.  Correctly sized equipment provides the best balance between affordability and efficiency.  Some of the factors considered include:

  • Climate and region of home
  • Orientation of home
  • Square Footage
  • Height of Space
  • Insulation in walls, roof, attic, etc.
  • Number, type, size, and location of windows and doors
  • Air tightness of the building
  • Duct leakage
  • Materials and assembly of construction
  • Number of occupants

Manual J – Room by Room Load Calculation

Maximum home occupant comfort is better achieved by analyzing the HVAC requirements for each individual room in the home.  Manual J can calculate requirements for these individual rooms or areas by using the Room by Room Load Calculation type.

Using the MiTek Wrightsoft software, the home is actually drawn out room (area) by room and the attributes of these rooms (areas) are assigned to them.  Now using the Manual J process, calculations are done in a more specific manner, producing an accurate load requirement on each individual room.

A Room by Room Load calculation allows you to determine how much air the HVAC system needs to supply each individual room for both heating and cooling.  Manual J calculates the heat loss and heat gain amounts for each room and then determines the air flow requirements for each individual room. The Manual J – Room by Room Load Calculation is required for projects such as:

  • Building a New Home (New Construction)
  • Renovating or Remodeling an Existing Home
  • Replacing an Existing HVAC Dust System

HVAC Systems, Zones, and Manual J

HVAC stands for heating, ventilation, and air conditioning, which describes the functions of an HVAC System.  An HVAC System is designed to control the environment in which it is placed in (the house).  Generally speaking, it controls the environment by moving and distributing air inside the rooms (areas).

An HVAC System is made up of the HVAC equipment, ductwork, controls, and terminations.  These include the heating and cooling equipment, all the duct lines that supply air to each room, the return lines, the grilles and diffusers, and the thermostat and other controls.  There may be only one HVAC system or multiple systems in a house.  For instance, a single-story home may have just one HVAC system that controls the entire house.  A two-story home may have two systems, one for the first floor and one for the second floor.  The type and size of a home are major factors when determining how many HVAC systems are required.  Noting for our purposes Ventilation is dealt with as a separate item and is not included in Manual J, as there are many different ventilation types and methods.

A Zone is a room, or space, or a set of rooms and spaces, which has its own point of temperature sensing and control (has its own thermostat).  Many people get HVAC Systems mistaken with Zones (Zoning).  You may only have zones within an HVAC system.  For Manual J purposes calculated with MiTek Wrightsoft RSU software an HVAC system that serves only one whole area is not classified as Zoned.  Now, if that same system controls two different areas, each area having its own thermostat, you now have an HVAC system with two (2) Zones.

When it comes to Zones (Zoning) each HVAC system you have is treated completely separate.  Thus, talking about Zones in a house with two (2) or more HVAC systems, you must look at each HVAC system separately.

Manual J is performed on each individual HVAC system.   Reports display calculations for each HVAC system.  If the HVAC system(s) is Zoned, then the reports will display zoned information as well.

Myth – Use Rules of Thumb to Calculate

Rules of Thumb Do Not Work.  Each home has its own unique properties and using a rule of thumb does not take into consideration the differences between each home.  When you take all the Manual J calculation source factors, you can easily see how different each home can be.  Rules of Thumb use a one size fits all approach.  Manual J calculates on an individual basis and thus produces accurate information for that particular home.

Tekneca Manual J – Load Calculation Services

Once you have acquired our Manual J Load Calculation Services, we will provide a complete room by room heating and cooling load calculation using the MiTek Wrightsoft Right-Suite software.  The Manual J calculations will produce a number of reports detailing required information for blueprints, building permits, contractors, and others.

A Tekneca, ACCA certified designer will review and assess your project from the information you have submitted to us.  We contact you with any questions we have and/or needed discussions about the project.  You will receive a detailed Room by Room Load Calculation package.

Want to see a sample of what you are getting.  Check out the Sample Manual J Report on this page.  Depending on your project, your Manual J Report will include some or all of these items.

Remember, to achieve maximum efficiency and comfort, follow and perform the ACCA’s System Design Process steps, first Manual J, then Manual S, and then Manual D.