ACCA Manual S • System Selection & Sizing
Right-size your HVAC system for comfort, efficiency, and code compliance.
Manual S turns your Manual J load calculation into an equipment selection that performs in the real world—proper capacity, airflow, and performance at Southern California design conditions.
What Manual S does
Equipment selection that matches the load—without oversizing.
Oversized systems can short-cycle, struggle with humidity control, and waste energy. Undersized systems can’t maintain setpoints on design days. Manual S provides a structured method to select heating and cooling equipment that aligns with the calculated loads and the manufacturer’s performance data.
Select capacity at design conditions (not nameplate)
Verify airflow and fan performance for the duct system
Confirm latent vs. sensible performance for comfort
Document assumptions for Title 24 and plan review
Our Manual S deliverables
What you receive
Clear, review-ready documentation that connects the load calculation to the selected equipment—so installers, inspectors, and owners are aligned.
Equipment schedule & selection rationale
Recommended system type and model family (furnace/AC, heat pump, dual fuel, packaged, etc.) with capacity targets and selection notes.
Performance verification from manufacturer data
Capacity and efficiency at expected operating conditions (including temperature and airflow assumptions), not just nominal ratings.
Airflow & static pressure targets
Design airflow, fan speed guidance, and static pressure targets to support duct design and commissioning.
Compliance-ready documentation
A concise package that supports Title 24 workflows and helps reduce back-and-forth during plan check.
How we size systems
A building-science process you can follow.
We start with Manual J loads, then select equipment using Manual S rules and manufacturer performance tables. The result is a system that’s sized for comfort, efficiency, and longevity—not guesswork.
✔
Right-size for comfort
Reduce short-cycling, improve temperature stability, and support better humidity control where applicable.
✔
Right-size for efficiency
Avoid oversizing that drives higher run losses and lower real-world performance—especially with heat pumps.
Manual S FAQs
Answers to common questions about system sizing and equipment selection.
Is Manual S required for Title 24?
Project requirements vary, but Manual S documentation is often requested to support equipment selection that aligns with Manual J loads and compliance documentation.
Why can’t we size by square footage?
Square footage ignores insulation levels, windows, orientation, infiltration, internal gains, and duct location—factors that can swing loads significantly.
What’s wrong with oversizing “to be safe”?
Oversizing can cause short run times, reduced comfort, more wear-and-tear, and lower efficiency. Proper sizing is the safer long-term choice.
Do you size for heat pumps differently than gas furnaces?
Yes. Heat pump performance changes with outdoor temperature and airflow. Manual S uses manufacturer data to confirm capacity at the conditions that matter.
Does Manual S include duct design?
Manual S informs airflow and fan requirements, but duct sizing and layout are addressed in Manual D. We can provide both for a complete design package.
Can you coordinate with my installer or architect?
Yes. We can review constraints, clarify assumptions, and provide documentation so the team can install and commission the system as designed.