New construction should be the easiest kind of Manual J.
In theory, the plans already contain the information you need.
In practice, HVAC contractors often receive a PDF set that is missing one critical item, contradicts itself, or shows architectural intent without final energy specifications.
The fastest workflow is to know exactly what to extract before you start modeling.
Start with the architectural floor plans
Pull:
- Room names
- Room dimensions
- Ceiling heights
- Floor-to-floor heights
- Conditioned floor area
- Stairs and open-to-below spaces
- Garage boundaries
- Bonus rooms
- Basement layout
- Mechanical-room location
Do not rely only on the plan's stated square footage.
Manual J is surface-based and room-based. You need the actual geometry.
Use elevations for exterior exposure
Elevations help you understand:
- Window placement
- Door placement
- Wall height
- Roof relationships
- Walkout-basement exposure
- Dormers
- Gable walls
- Overhangs
- Orientation clues
A floor plan alone can hide vertical exposure that affects load.
Sections are where thermal boundaries become clear
Building sections are especially useful for:
- Vaulted ceilings
- Knee walls
- Attic boundaries
- Cathedral roofs
- Bonus rooms over garages
- Conditioned crawlspaces
- Basement walls
- Floor assemblies
If you are unsure whether a surface separates conditioned space from outdoors or another buffer space, the section drawing is often the answer.
Find the insulation schedule
Look for:
- Wall R-value or U-factor
- Ceiling/roof R-value
- Floor insulation
- Foundation insulation
- Slab-edge insulation
- Continuous exterior insulation
- Spray-foam assemblies
- Crawlspace-wall insulation
Do not assume the current energy code minimum if the project documents specify something else.
The Manual J should model the house that will actually be built.
Find the window schedule
You want:
- Window dimensions
- Quantity
- U-factor
- SHGC
- Product series if specified
If the schedule gives rough openings but the glazing specification gives actual unit performance, use the appropriate data for the calculation.
Do not reduce a detailed window package to "double pane."
See How Window U-Factor and SHGC Affect a Manual J.
Confirm orientation
A correct floor plan with the wrong north arrow can still produce a wrong cooling distribution.
Confirm:
- Site plan north
- Building orientation on the lot
- Whether the architectural plan has been rotated for sheet layout
This matters most when the project has large east- or west-facing glass.
Check the mechanical ventilation design
New homes are often tighter and more likely to use intentional ventilation.
Look for:
- ERV
- HRV
- Fresh-air duct
- Dedicated ventilation system
- Specified outdoor airflow
- Exhaust-based system
Manual J includes the load created by outdoor air, but it does not decide how much ventilation the building should have.
That airflow comes from the ventilation design and applicable requirements.
Check the air-sealing target
If the project has a blower-door target, record it.
New construction may specify a maximum ACH50.
Be careful about modeling a target as if it is a measured final result.
For design, the project specification may be the best available assumption.
After testing, the measured value can be used if the workflow and project requirements call for updating the model.
Identify duct location
Plans should tell you whether ducts are:
- Inside conditioned space
- In a vented attic
- In an encapsulated attic
- In floor trusses
- In a crawlspace
- In a garage chase
Duct location can change the system load.
Do not wait until Manual D to notice that half the supply system is outside the thermal boundary.
Decide system zones before finalizing room assignments
If the house has multiple HVAC systems, decide which rooms each system serves.
Common splits include:
- First floor / second floor
- Main house / primary suite
- Main house / finished basement
- East wing / west wing
The Manual J system totals depend on room assignment.
See Multiple HVAC Systems: How to Split a House for Manual J for more detail.
Watch for plan conflicts
Common conflicts include:
- Floor plan says 9-foot ceiling; section says 10 feet
- Window schedule changed but elevations did not
- Energy sheet specifies one insulation level; wall detail shows another
- Attic is labeled conditioned on one sheet and vented on another
- Addition revision never reached the HVAC contractor
Do not quietly pick whichever value produces the load you expected.
Flag the conflict and get clarification.
Plans change
New construction Manual J is often completed before every finish and product is final.
That is normal.
The goal is to keep the model synchronized with material changes.
Revisit the calculation if the project changes:
- Window package
- Insulation
- Conditioned area
- Ceiling heights
- Attic strategy
- Ventilation
- System zoning
A load calculation based on the permit set may no longer describe the final house after major revisions.
A practical plan-review order
- Site plan: orientation
- Floor plans: room geometry
- Elevations: windows and exterior exposure
- Sections: thermal boundary
- Wall/roof details: assemblies
- Window schedule: U-factor and SHGC
- Energy notes: insulation and air sealing
- Mechanical notes: ventilation
- HVAC plans: system zoning and duct location
That order prevents a lot of rework.
Bottom line
A plan-based Manual J should be faster than an existing-home field survey because the building information is already documented.
But the plans only help if you pull the right information and resolve contradictions.
Build the load model from the actual project specifications, not generic defaults.