An HVAC business platform with real duct engineering built in.
One system to run a US residential HVAC contractor end-to-end — CRM, e-signed proposals, online payments, purchasing, payroll — with an ACCA Manual J/D duct-design engine most contractor software doesn't have. Built for a non-technical, Spanish-speaking owner.
Result
One system replacing 5+ tools · proposals in minutes · real Manual J/D
A US residential HVAC contractor needed one system to run the business — and something no off-the-shelf tool offered: correct duct engineering. We built both into a single platform.
At a glance
- 24 data models and 25+ screens spanning CRM, finance, and engineering
- 5+ disconnected tools and spreadsheets replaced by a single system
- Proposals and contracts that took an hour by hand now go out in minutes
- Duct sizing re-engineered from a velocity rule of thumb to verifiable ACCA Manual J/D
Background
The shop ran on paper, spreadsheets, and a few disconnected apps. Nothing tied a lead to a job to an invoice, proposals were slow and inconsistent, and there was no way to take a card online.
The bigger issue was in the field. Duct sizing was done with a velocity-only rule of thumb — the method that produces a 5-inch duct for 110 CFM. It reads as a minor number; in practice it drives callbacks: noise, weak airflow, comfort complaints. The tools the shop had didn't do the engineering, and the installs carried the cost.
Approach
We built the engineering into the platform rather than bolting another quote-and-invoice app onto the problem.
Duct sizing uses the ACCA Manual D equal-friction method — velocity-capped, with total-system static pressure — fed by a Manual J per-room load calculation that accounts for window U-factor and SHGC, orientation, and solar gain. An auto-routing step turns that into a design: place the air handler and supply boots, and it produces a reducing trunk-and-branch layout, supply and return, sized per segment. The engines run against an automated test suite and generate PDF proofs, so the numbers are checkable rather than trusted.
Around that, the rest of the company runs from one login: CRM and projects; proposals and Home Improvement Contracts as branded PDFs with BoldSign e-signature; Stripe payments via shareable links, with receipts and invoices generated automatically; and purchasing, inventory, payroll, and reporting.
Constraints
The owner is non-technical and works primarily in Spanish. The interface reflects that — a guided flow from load calculation through to design, in plain steps — so the depth stays under the surface where it belongs.
Stack
React and TypeScript with a Konva canvas for the CAD tool; a typed Node/Express and Prisma backend; Stripe, BoldSign, and Resend.
In production
The platform runs the contractor's operation end-to-end and has replaced the shop's paper-and-spreadsheet workflow entirely. It's a working system in daily use, and it continues to ship against feedback from the field.
Related reading: Most HVAC software still sizes ducts wrong.
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