Professional Manual J/S/D Calculations Without the Enterprise Price Tag
Room-by-room load calculations, equipment sizing, and duct design in a modern web app. Manual J methodology, not rules of thumb.
Free during beta
| Room | Heating | Cooling | CFM |
|---|---|---|---|
| Living Room | 8,240 | 6,180 | 185 |
| Primary Bedroom | 5,120 | 4,890 | 146 |
| Kitchen | 4,680 | 5,410 | 162 |
| Bedroom 2 | 3,960 | 3,240 | 97 |
| Bathroom | 2,180 | 1,640 | 49 |
| Building Total | 24,180 | 21,360 | 639 |
The problem
Professional load calculation software costs $2,500-4,800/year and chains you to a desktop. Most contractors skip Manual J entirely and oversize by 20-40%, wasting energy, creating humidity problems, and shortening equipment life.
- Wrightsoft costs $400/mo and requires a Windows desktop — measure in the field, drive back to the office, then return with a proposal
- CoolCalc is web-based but Manual S equipment selection is still in Beta — you can calculate loads but not properly size equipment
- AutoHVAC is fast and affordable but has no Manual S equipment selection and no Manual D duct design
- Heat pump sizing requires balance point analysis and COP curves that no affordable tool provides — most contractors just oversize and hope
- Psychrometric charts cost $149-299 as a separate tool or are buried in $900/yr commercial software
What it does
Manual J Room-by-Room Load Calculation
Follows Manual J 8th Edition methodology with Addenda A-D. Sensible and latent cooling loads, heating loads, and ventilation loads for every room. Envelope, infiltration, ventilation, internal gains, and solar gain components — all traceable to your inputs.
Manual S Equipment Selection
Match manufacturer equipment to your calculated loads within ACCA sizing limits (95-115% cooling, 140% heating). Performance data from 100+ brands interpolated to your actual design conditions, not just rated capacity.
Manual D Duct Design
Size supply and return ductwork using equal friction or velocity reduction methods. Fitting loss database, static pressure budget tracking, and velocity checking to prevent noise and airflow problems.
Heat Pump Design Workflow
Balance point analysis, COP curves at actual conditions, dual-fuel scenario modeling, variable-speed capacity curves, and cold-climate HP support. Designed for heat pumps first — not bolted onto a gas furnace workflow.
Interactive Psychrometric Chart
ASHRAE-standard psychrometric chart with air process simulation. Heating, cooling, humidification, dehumidification, and mixing processes. Coil analysis with apparatus dew point and SHR calculation.
Sensitivity Analysis
Change windows from double-pane to triple-pane and instantly see the load impact in BTU/hr. Compare scenarios side by side. Every assumed input flagged so you know where uncertainty lives.
Permit-Ready PDF Reports
Manual J, S, and D reports formatted for building department submission. Room-by-room load tables, equipment sizing compliance, duct schedules, PE stamp area, and full audit trail of every input assumption.
ASHRAE Design Conditions Database
TMY3/DOE weather data for every US location. Look up by ZIP code — 1% cooling dry-bulb, 99% heating dry-bulb, humidity ratios, altitude corrections, and IECC climate zone classification.
Why switch
Complete J/S/D at a Fraction of the Cost
The only affordable web-based tool with ACCA-methodology Manual J, Manual S equipment selection, and Manual D duct design. Wrightsoft charges $4,800/yr for the same workflow.
Heat Pump-First Design
Balance point analysis, COP curves at actual outdoor temperatures, dual-fuel crossover modeling, and variable-speed capacity curves. Built for the electrification transition, not retrofitted onto a gas furnace tool.
Web-Based, Any Device
Run load calculations from a tablet on-site, review results on your phone, generate reports from your desk. No Windows desktop required. No two-visit workflow.
Psychrometrics Included
Interactive psychrometric chart with coil analysis, mixed-air calculations, and SHR-based equipment matching — included in every plan. Competitors charge $149-299 separately.
Free tools
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