Our expertise · Building Performance & Engineering
Manual J Load Calculations
Size the system from the home's real load, not from a rule of thumb.
A rule of thumb sizes equipment by floor area alone, and floor area says very little about how a home gains and loses heat. Orientation, window area and performance, envelope assemblies, infiltration, ventilation and the local design conditions do the real work, which is why two homes of the same size can need different equipment, and why a system sized by allowance is as likely to be too large as too small. Manual J replaces the allowance with a documented, room-by-room calculation of what the home actually needs. Green Summit prepares residential heating and cooling load calculations as a defined part of building-systems design support, connecting the calculation with the building design, the selected equipment and the documentation the project team needs.
- Licensed engineering firm
- RESNET Rating Provider No. 1998-221
- Founded 2014
- Engineered substantiation, not estimates
Who this is for
Developers, builders and design teams, housing authorities, Tribal housing programs and HERS Raters who need a documented residential load calculation behind the equipment they specify.
What we do
- Review the inputs. Plans, orientation, envelope details, windows, infiltration assumptions, ventilation and design conditions establish the basis of the analysis, and we flag what is missing before we calculate.
- Calculate and coordinate. We prepare room-by-room and whole-dwelling loads and identify the inconsistencies that need a design-team decision.
- Control the revisions. When a material building or equipment change affects the result, we update the analysis and reissue it, so the calculation on file describes the home being built.
Our process
- Define the dwelling, the system and the output required. We settle what is being calculated and what the deliverable has to support.
- Review the inputs and complete the project-specific calculation. We document every assumption alongside the result.
- Resolve questions, issue the deliverable and identify any field-verification needs. The calculation goes to the people who will select equipment, design ducts and pull the permit.
Benefits
- Documented assumptions instead of informal sizing rules.
- A clearer connection between the building design, the equipment and the airflow it needs.
- Information the team can use for permitting, contractor coordination and related certification work.
Why Green Summit
Green Summit is a consulting partner delivering end-to-end compliance solutions in building performance, specialty tax incentives and advisory services. Founded in 2014, we are a licensed engineering firm and RESNET Rating Provider No. 1998-221, and our modeling and field-verification experience keeps the design calculation connected to what will actually be installed. The numbers we deliver are engineered substantiation, not estimates.
The local jurisdiction determines the submittal requirements and any required professional seal, and we tell you at the outset what your jurisdiction expects. Where the project also carries an energy-code pathway or a certification, the same team keeps the load calculation consistent with the model and the field verification.
Frequently asked questions
What is a Manual J load calculation?
Manual J is the ACCA procedure for calculating a home's heating and cooling loads: the heat it gains and loses at design conditions through its walls, roof, windows and floors, through infiltration and ventilation, and from internal sources. The result, room by room and for the whole dwelling, is the basis for selecting equipment under Manual S and designing ducts under Manual D. It documents every input, so anyone reviewing the design can see where the numbers came from.
Can square footage alone determine system size?
No. Orientation, envelope performance, windows, infiltration, ventilation and design conditions all change the load, and a square-foot allowance ignores every one of them. The calculation documents those inputs instead of assuming them away.
Do you provide room-by-room results?
Yes, where the project needs them to support airflow and duct design. We define the dwelling, the zones and the documentation required before we start.
Which records should we provide?
Plans, orientation, envelope details, windows, infiltration assumptions, ventilation and design conditions. We flag missing information and settle any assumptions with you before issuing the final analysis.
Can you coordinate this with the other Manual calculations?
Yes. Manual J establishes the loads, Manual S supports equipment selection and Manual D supports duct design. We scope them together so the inputs and decisions stay consistent from the load to the last register.
Does the calculation guarantee comfort or code approval?
No. Installation, balancing, controls, how the home is actually used and the authority's review all matter. The calculation documents a defined design analysis, and we never present it as a promise about every aspect of installed performance.
Let's start your design with the load.
Tell us the dwelling type, where it is, the stage of design and whether you also need equipment selection or duct design.
Related solutions
- MEP, HVAC & Hot-Water Coordination
- Residential Energy-Code Compliance
- Energy Modeling
- Manual S Equipment Selection
- Building Systems Commissioning & Functional Verification
Program and technical references
ACCA: Manual J
Program information reviewed September 22, 2026. Current applicability, qualifications and program terms are confirmed for each engagement.
Or call 321-273-2200 · inquiry@greensummit.com