Manual S Calculations

Tekneca Manual S – Equipment Selection Services

What is Manual S

Manual S is the second step in designing your HVAC system.  Using the heating and cooling loads that were calculated in Manual J, you can now size and select the HVAC equipment to match your requirements.  Occupant satisfaction is maximized when the heating and cooling equipment is the correct type and size to meet the capacity requirements from the Manual J load calculations.

When it comes to residential equipment selections, the ACCA’s Manual S is the only procedure recognized by the American National Standards Institute (ANSI).

Manual S provides sizing rules that set upper and lower limits for equipment total capacity and provides specific procedures for selecting HVAC equipment.  The HVAC Designer must use manufacturers’ (OEM) performance data, the capacity values must be for operating conditions and the equipment must satisfy load and design requirements from Manual J.

Manual S is a complete equipment analysis, calculation, selection, and report.  Analysis of the load requirements, calculation using the equipment’s OEM data, and selection of proper equipment.  Manual S provides a report certifying that the selected meets the needs produced by Manual J.

Reasons to Use Manual S on the A/C and Heating System

  • Manual S is a requirement in the International Residential Code (IRC)
  • Equipment that is properly sized will provide comfortable conditions for the occupants
  • Avoid the risk of purchasing improperly sized equipment, which can cause poor efficiency and contribute to less comfort.
  • Reduces maintenance costs over the equipment’s lifetime
  • Longer equipment life expectancies

Problems Caused from Wrong Sized Equipment

Undersized equipment
  • Will not meet the occupant’s comfort requirements at the design conditions.
  • Equipment will run too long, trying to meet needs that it is not capable of, thus causing damage and increased wear and tear on the equipment
Oversized equipment can create problems
  • Equipment starting and stopping (short-cycling) frequently causing temperature swings throughout the house
  • Short cycling also causes increased wear on the equipment which raises maintenance costs.
  • Reduced summer humidity control
  • Increased potential for mold growth
  • Oversized equipment generally requires larger ducts, increased electrical usage, and larger components causing higher install and operating costs
ANSI Manual S Cover
Sample Manual S Report
Sample Manual S Report

Myth – Oversizing is Better

Bigger is not always better.  Oversized equipment will not operate effectively and can cause comfort problems and cost you using extra energy.  Improper sizing can cause a mixture of problems including poor comfort, IAQ concerns, equipment durability issues and ineffective moisture control.  Also, if you install a system that is too big than you can run into short cycling, which means that the furnace or air conditioner will turn on and off to frequently and the shorter the cycle, the harder your system needs to work, causing wear and tear on that system.

Tekneca Manual S – Equipment Selection Services

Now that the Manual J process has been completed, we now know the load requirements of your project.  We use these load requirements to perform the Manual S process and select the equipment.

We take the Manual J load requirements and then using Manual S and the equipment specifications that you provided, we determine the proper equipment size selection. We assess the manufacturer’s equipment performance data including data such as capacities, blower motors, temperatures, cfm, and friction rates. Manual S methods allow us to interpolate your equipment’s capacity and performance and then size the equipment to match your project’s design conditions.

Want to see a sample of what you are getting.  Check out the Sample Manual S Report on this page.  Depending on your project, your Manual S 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, then Manual D.