κ · Manual J load calculation
The modern Manual J.
Engineer-grade math, contractor-grade UX. Transparent residential heating & cooling loads — validated within ±5%, free to start.
The number the whole system rides on
Manual J shouldn’t be this painful.
- Manual J means heavy desktop software, a clunky install, and a half-day of training.
- Or a pay-per-project black box that won’t show you a single equation.
- So you rule-of-thumb it — and oversize the equipment that short-cycles and kills comfort.
- An undersized call gets flagged at inspection. A redo on your dime.
- Either way you’re guessing on the one number the whole system is built on.
Engineer-grade math, contractor-grade UX
A load you can defend — in minutes, on the truck.
No black box. Every BTU traces to the physics, and you can open the breakdown on any result.
Transparent math
Every BTU traces to physics — Q=U·A·ΔT, infiltration, ventilation, solar. Open the breakdown on any result. No black-box AI.
Validated ±5%
Calibrated against the NREL/DOE federal reference house. 98 automated tests on the load engine.
Fast & mobile
Five steps to a sized load on any device. Printable permit-style report. No desktop install, no training.
What you get
- Size to the actual load — no more short-cycling oversized units.
- Walk into inspection with a report that shows its work.
- Quote faster: a sized load in minutes, on the truck.
- Defend every number — open the breakdown in front of the customer.
- Free to start. No account, no install.
- Flat pricing planned — not a fee on every single project.
Pricing
Free now. Pro priced in the open.
The full calculator is free today — no account. Paid plans ship with sign-in; we list the planned prices instead of hiding them. No fake trial until billing is live.
Pro Solo
$49/mo
or $468/yr · 14-day trial
Saved projects, room-by-room, Manual S, branded PDF.
Pro Team
$179/mo
Everything in Solo, for the whole crew.
Founder
$699 once
100 seats · lifetime
Locked-in price + roadmap input.
Single permit report at $19. Billing via Paddle (Merchant of Record, USD). Planned prices as of June 2026 — may change before launch.
The proof is the math
Validated, not vibes.
New software, no recycled reviews. The credibility is the engine: calibrated against a federal reference house and covered by automated tests. Open any result and check the physics yourself.
±5%
vs NREL house
98
engine tests
J + S
Manual J & S
Straight answers
Is this ACCA-approved for permits?
Not yet — ACCA software approval is a separate certification we’re pursuing. Today Kappa is a fast, transparent estimating & design tool. In jurisdictions that require an approved stamp, size confidently here and pair with your approved workflow.
How accurate is it?
Calibrated within ±5% of the NREL/DOE federal reference house, with 98 automated tests on the load engine. Every result shows the physics behind it.
Is it really free?
Yes — run a full load with no account. A Pro tier (saved projects, room-by-room, exports) is coming with flat pricing.
Do I have to ditch my current software?
No. Use Kappa to size fast and sanity-check, then pair it with whatever your jurisdiction requires.
FAQ
What does it calculate?
Residential Manual J heating & cooling loads — envelope, infiltration, ventilation (ASHRAE 62.2), internal & solar gains, plus equipment sizing (Manual S).
Do I need to install anything?
No. It runs in the browser, on any device. Five steps to a sized load.
Can I print a report?
Yes — a permit-style report (detailed for the file, summary for the homeowner), printable straight from the browser.
What’s the climate data?
ACCA-style design conditions per station. (Data licensing is being finalized for the commercial release.)
When is Pro available?
The free calculator is live now. Pro (saved projects, room-by-room, exports) is planned — it ships with sign-in and flat pricing. No fake trial in the meantime.
Sized on physics,
not a rule of thumb.
A Manual J you can run on the truck and defend at inspection.
Try Kappa freeP.S. — Oversize and it short-cycles. Undersize and it fails inspection. Kappa sizes to the real load and shows the physics — free to run, today.