For iPhone · iOS 18+
Water heater sizing on your iPhone
The same sizing engine as this site, in your pocket and offline. Size a tank by First Hour Rating or a tankless unit by GPM at your rise in seconds, free. Lifetime Pro adds comparison, saved jobs and PDF reports for $4.99, once.
Free vs. Lifetime Pro
| Feature | Free | Lifetime Pro |
|---|---|---|
| Tank sizing: minimum First Hour Rating | ✓ | ✓ |
| Tankless sizing: GPM at your rise and heat load | ✓ | ✓ |
| Built-in fixture library with sources | ✓ | ✓ |
| Works offline, no account, no ads | ✓ | ✓ |
| Tank vs. tankless comparison for the same job | — | ✓ |
| Custom fixtures; edit flow, duration and temperature | — | ✓ |
| Design margin and heater efficiency | — | ✓ |
| Gas input (BTU/hr) or electric input (kW) | — | ✓ |
| Check a specific water heater against the requirement | — | ✓ |
| Every step of the calculation | — | ✓ |
| Saved jobs with notes: reopen, edit, duplicate | — | ✓ |
| PDF reports for customers, inspectors or your files | — | ✓ |
Lifetime Pro is a one-time in-app purchase, $4.99 in the U.S. The App Store shows the price for your country.
Built for the job site
- Works offline. Basements and crawlspaces don’t need signal.
- Big, easy targets. Large, easy-to-tap controls, Dark Mode and larger text support.
- Shows its work. Every formula, default and source is in the app, the same as our methodology page.
- Reports customers can read. Pro exports a PDF with the job, design conditions, demand, calculation steps and assumptions.
- Private. No account, no ads, no tracking. Jobs stay on your phone.
Who uses it
Plumbers and HVAC technicians quoting a replacement, contractors and builders speccing new homes, property managers, and homeowners who want a better answer than “get the same size as last time.”
Get Water Heater Sizing Calculator
Free on the App Store for iPhone.
About the app
Is the app free?
Yes. Basic tank and tankless sizing is free with no calculation limit, account or subscription. Lifetime Pro is a single $4.99 in-app purchase (U.S. price) that adds the professional tools.
Is Lifetime Pro a subscription?
No. It is a one-time, non-consumable purchase. Buy it once and restore it on any iPhone signed in with the same Apple Account, from Settings → Restore Purchases in the app.
Does the app give the same answers as this website?
Yes. The website's calculators are a port of the app's sizing engine and are tested against it for identical results, including rounding and every warning.
Does the app collect my data?
No. Calculations and saved jobs stay on your iPhone. There is no account, analytics, advertising or tracking. Purchases are handled by Apple.
Which iPhones does it support?
iPhone running iOS 18 or later. It supports Dark Mode and larger text sizes.