Supported Features
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Dark Interface
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Differentiate Without Color Alone
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Sufficient Contrast
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Reduced Motion
HVAC Load Calculator Manual J
BTU Sizing for Contractors
Free · In‑App Purchases · Designed for iPad. Not verified for macOS.
The Manual J HVAC Load Calculator is the one HVAC contractors actually want to use.
Stop overpaying for clunky, over-engineered calculators designed for engineers. HVAC Load Calculator brings professional Manual J calculations to your iPhone or iPad device — clean, modern, offline-ready, and built for the field.
BUILT FOR HVAC PROFESSIONALS
Unlike expensive desktop software shoehorned onto mobile, we designed this from scratch for techs working in the field. Large buttons you can tap with gloves on. Fast calculations while standing in a basement. Professional reports that win homeowner trust.
THREE LEVELS OF ACCURACY
Simple Mode – 8 inputs
Regional ZIP-code benchmarks and square-footage multipliers. Get an estimate in under 60 seconds with zero measurements. Perfect for quick quotes and initial sales conversations.
Moderate Mode – Standard Accuracy (Whole-House Block Load) – 15 inputs
Component-level factors: insulation quality, window types, foundation — with a conservative safety buffer. Prevents undersizing while staying accessible for non-engineers. The sweet spot for standard replacement jobs.
Pro Mode – Professional Grade (Detailed Whole-House Block Load) – 16 inputs + pro overrides
Full MJ8 physics: altitude-adjusted density, solar load factors, CLTD daily-range lag, and separated duct analysis. Maximizes equipment life and comfort — often right-sizing by 1+ ton. Best for new construction, high-performance builds, and detailed equipment sizing.
NOW AVAILABLE WORLDWIDE
US Mode: ZIP code lookup with 28,000+ ZIP code climate database
International mode lets you enter your city, country, and local design temperatures directly — no ZIP code required. Choose your climate zone and moisture regime, and the calculator handles the rest.
Metric Units: Toggle between Imperial and SI (kW, m², m³/h) throughout the app and PDF reports
WORKS IN THE FIELD
Offline-First – No signal in the basement? No problem. Everything runs locally on your device.
Auto-Save Projects – Every calculation saves automatically. Never lose your work.
Professional PDF Reports – Generate and share detailed load reports from your phone or tablet.
Site Photo Documentation – Capture tagged photos, label by location and component, add notes, and include a professional photo appendix in your reports.
iPad & Tablet Support – Optimized layouts give you more room to work on-site or back at the office.
THE MATH YOU TRUST
Calculations follow ACCA Manual J 8th Edition methodology:
– Cooling BTU/hr (sensible and latent loads)
– Heating BTU/hr
– Recommended tonnage (rounded to 0.5 tons)
– Recommended furnace size (rounded to 5,000 BTU)
– Manual S equipment sizing guidance
– Kitchen/appliance heat gain per MJ8 Table 4
Tap "How Our Calculator Works" for a plain-English guide to every input and how it shapes your results.
WHY CONTRACTORS CHOOSE US
– Modern, intuitive interface that makes sense the first time you use it
– Dark mode and system theme support
– Fast performance, even on older devices
– Privacy-first: your data stays on your device
– Free to start — then $4.99/year
PERFECT FOR
HVAC contractors, installers, and service techs
Sales teams quoting new systems
Independent contractors building their business
International professionals working in metric
Home inspectors documenting HVAC systems
No account. No setup. Just open the app and get to work.
Terms of Use (EULA): https://www.apple.com/legal/internet-services/itunes/dev/stdeula/
• Streamlined data entry — a cleaner project form with the essential inputs up front and extra options tucked away until you need them.
• New wall and roof/ceiling insulation options for more accurate load calculations.
The developer, Mike Watson, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy .
Data Not Collected
The developer does not collect any data from this app.
The developer indicated that this app supports the following accessibility features. Learn More
Information
- Seller
- Mike Watson
- Size
- 48.3 MB
- Category
- Utilities
- Compatibility
Requires iOS 15.1 or later.
- iPhone
Requires iOS 15.1 or later. - iPad
Requires iPadOS 15.1 or later. - iPod touch
Requires iOS 15.1 or later. - Mac
Requires macOS 12.0 or later and a Mac with Apple M1 chip or later. - Apple Vision
Requires visionOS 1.0 or later.
- iPhone
- Languages
- English
- Age Rating
4+
- 4+
- In-App Purchases
Yes
- Annual Pro with Trial $9.99
- Annual Pro with Trial $4.99
- Annual Pro with Trial $7.99
- HVAC Load Calculator Pro $9.99
- HVAC Load Calculator Pro $19.99
- Copyright
- © 2026 Mike Watson