HVAC contractors are hard to find, especially if you don’t know the right questions to ask. In order to properly vet your prospective HVAC contractors, it’s important to know what Manuals J, S, T, and D are.
These HVAC technical manuals are the basis for proper HVAC installations and most technicians worth their salt will follow them to a T. Unfortunately, over half of all HVAC systems are improperly installed, which can increase inefficiencies by as much as 30%!
Although Manuals J, S, T, and D are very complicated, here is a basic introduction to what they are and why they’re important for a properly designed HVAC system. All of the manuals are published and sold by the Air Conditioning Contractors of America (ACCA).
Manual J – Heating and Cooling Load Calculations
If you are an HVAC contractor or home energy rater, you know what Manual J is and how important it is for properly sizing an HVAC system. These HVAC guidelines apply to any residential unit that has a HVAC and exhaust system:
- Single-family detached structures, duplex structures, and triplex structures
- Single-family attached structures (row house or town house)
- Dwelling units in multi-family attached structures (condo and apartment units)
- Energy-efficient homes
Manual J outlines the requirements for conducting a “load calculation” on the home, such as measuring insulation and ventilation levels. Other considerations include air duct tightness and the number of heat-producing appliances and people.
Each room’s results specify how many British thermal units (BTUs) are lost in the winter and how many are gained in the summer.
After measuring each room’s sensible (temperature-related) and latent (humidity-related) heat, the technician can then determine how much conditioned air that room requires. It is necessary to conduct this inspection prior to sizing a system so that you end up with a properly sized HVAC system.
Manual S – Heating and Cooling Sizing and Selection
Once you have the load calculation completed using Manual J, Manual S shows you how to select the proper equipment for the job, providing “sizing requirements for 11 types of cooling and heating equipment, as well as in-depth explanations and examples of how to use manufacturer's performance data” (ACCA).
Manual S contains a lot of information regarding equipment sizing, ventilation, and airflow, taking into consideration sensible and latent heat, amount of airflow, and static pressures. This manual, combined with the load calculations from Manual J, gives the technician the technical information for selecting the proper system for your home, whether it’s an air conditioner, heat pump, furnace or boiler.
Manual T – Air Distribution Basics
Manual T has to do with your HVAC’s air distribution. “It shows you, in step-by-step detail, how to select, size, and locate the supply air diffusers, grilles and registers, and the return grilles. It gives you examples of how to use manufacturers comprehensive performance data, calculate pressure losses, and control noise” (ACCA).
After running a Manual J calculation, Manual T helps to answer questions like: Where will supply and return registers go? What type of grill, vent, or diffuser will be used?
Manual T calculations improve the airflow in your home so you aren’t getting drafts or inadequate airflow. Manual J might be able to calculate proper conditioned air levels, but if the airflow is weak, the air will feel stagnant and uncomfortable.
Manual D – Heating and Cooling Duct Design
Manual D works in conjunction with the other manuals to provide proper design, sizing, and installation of residential duct systems. After you have determined the heating and cooling loads (Manual J), selected the right HVAC equipment (Manual S), and figured out how to distribute the air (Manual T), you can now design the duct system (Manual D).
Ductwork design is extremely important to prevent air and energy leaks, in addition to humidity and moisture problems. Poor ductwork design can seriously affect your comfort and indoor air quality.
Manual D includes information for determining the best duct design for the available space, including how to properly size, seal, and insulate air ducts.
These four manuals are necessary for properly installing a new HVAC system. Make sure you confirm with your prospective HVAC contractors that they use ACCA’s manuals for their HVAC installations and replacements.
Shopping for a new A/C requires a bit of work, but finding the right one will ensure consistent, dependable comfort for years to come. If you are in the market for a new unit, start your search with Hiller. We offer quality HVAC service, stock all the popular brands and have an affordable maintenance plan to keep your system running efficiently.
For more advice on replacing or installing a new HVAC system, read What to Know Before Buying a New Air Conditioner.