Use case
Manual J for new construction — preliminary sizing before drawings finalize.
Your subcontractor needs a number now, before the energy consultant stamps the drawings. Excel takes 30 minutes per revision. BuildSolver runs the preliminary Manual J at design-development inputs in about 90 seconds — same ACCA procedures, fewer ceremonies.
Example project
1,800 sq.ft 2-story single-family · Dallas, TX 75201 · design-development phase · framing schedule done · no finalized energy drawings yet.
FOR ESTIMATION ONLY · ACCA MJ8 §6.4
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01 · The problem
Design-dev numbers can’t wait for stamped drawings.
- The framing schedule is locked in weeks before the energy consultant’s permit-grade Manual J. Mechanical, electrical, and the duct subcontractor all need preliminary loads first.
- Excel Manual J takes 30 minutes per revision. Three design revisions = 90 minutes you don’t have during framing.
- Wrightsoft and Cool Calc are built for permit submittal — a full input ceremony, room-by-room. Overkill for the preliminary number.
02 · How it works
Describe the design intent; get a preliminary number.
- Describe the design.Footprint, stories, location, framing type, target R-values, window-to-wall ratio. IECC defaults fill in what you haven’t decided yet.
- BuildSolver runs the preliminary Manual J. Deterministic code, ACCA Manual J 8th Edition §6 (sensible) + §8 (latent). Block load, not room-by-room.
- Iterate as the spec firms up. Sessions save in your account; rerun with updated inputs as the design develops.
03 · Where this fits in the workflow
Preliminary sizing first; permit-grade later.
BuildSolver covers the design-development through bid stage: framing decisions, duct chase routing, condenser pad location, electrical service sizing. For the permit submittal, your energy consultant or mechanical engineer runs the room-by-room Manual J in Wrightsoft or Cool Calc. The two numbers usually match within 10–15% when the same envelope assumptions are used.
04 · BuildSolver vs Excel
Same Manual J, faster iteration.
Excel sheets handed down over years are common in design-build firms. They work — but every revision takes 30 minutes, and the error budget is huge (lookup-table mistakes, formula cell-reference bugs, missing latent terms).
| Feature | BuildSolver | Excel sheet |
|---|---|---|
| Time per revision | ~90 seconds | ~30 minutes |
| Error budget | Deterministic code, golden tests | Cell-reference bugs, lookup mistakes |
| Audit trail | Inputs + citations logged on every run | Whatever the previous user saved |
| Mobile | Yes | Excel mobile is painful |
| Multi-iteration storage | Session history per project | File-per-revision sprawl |
05 · FAQ
Common questions about new construction sizing.
+Is preliminary sizing good enough for framing decisions?
Yes — and it’s the right tool for the stage. Manual J at design-dev level gets the framing and rough-in correct: duct chases, condenser pad location, electrical service. The permit-grade Manual J refines numbers once windows, insulation specs, and ventilation are pinned down.
+How early in construction can I run this?
As early as schematic design — you only need square footage, location, basic envelope assumptions, and orientation. BuildSolver fills in IECC climate defaults; you can rerun as the spec firms up.
+What inputs do I need before drawings are final?
Footprint and stories, ZIP code, framing type (2x4 / 2x6 / SIP / ICF), window-to-wall ratio estimate, insulation target (R-values). The chat asks for what it needs and will use IECC defaults for anything you haven’t decided yet.
+Will this match the permit-grade Manual J?
Usually within 10–15% when the same assumptions are used. The permit-grade calc accounts for room-by-room loads, exact window specs, infiltration testing data, and ventilation per IECC R403.6. Use BuildSolver for the early-stage number, Wrightsoft or Cool Calc for the final.
+Can I rerun it as drawings change?
Yes. Each session is saved in your account; you can iterate as the design firms up. Pro and Team tiers also unlock the project-report PDF, which compares iterations in one document.
+What's the difference between preliminary and permit-grade Manual J?
Preliminary uses building-level inputs with code defaults — block load only. Permit-grade is room-by-room, uses measured infiltration (blower-door data when required), and is run in an ACCA-approved package so an AHJ accepts the printout. BuildSolver targets preliminary; Wrightsoft / Cool Calc target permit-grade.
Run the preliminary now; refine as the design firms up.
Free tier covers 10 calculations per day. Each session saves so you can iterate. Pro tier adds your firm’s branding to the handout PDF.
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