Boiler Sizing Calculator: Horsepower, lb/hr, and Btu/hr
Size a boiler from your steam load, equipment list, or batch heating job, and see the recommended setup, fuel use, and the South Coast AQMD rule that applies. From the engineers at McKenna Boiler Works, Inc., a boiler manufacturer in California.
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McKenna Boiler Works, Inc.’s boiler sizing calculator converts boiler horsepower to steam output in lb/hr, heat output in Btu/hr and kW, and fuel input, and shows which South Coast AQMD NOx rule applies. One boiler horsepower equals 34.5 lb/hr of steam from and at 212°F, or 33,475 Btu/hr. The South Coast rule follows the nameplate rated heat input: Rule 1146.2 up to 2,000,000 Btu/hr, Rule 1146.1 above 2 and below 5 million Btu/hr, and Rule 1146 at 5 million Btu/hr and above. McKenna builds firetube, firebox, and vertical boilers in Oceanside, California. Call (323) 987-1816 or email info@mckennaboiler.com to size a boiler for your load.
Calculator
Size a boiler.
Size your boiler plant
Answer three steps. Results update as you type.
1The load
2Operating conditions
3Plant setup
Results
| Heat output required | |
| Steam, from and at 212°F rating | |
| Fuel input, recommended setup | |
| Natural gas at full fire | |
| Estimated fuel cost per year |
Estimates for planning. McKenna engineers confirm sizing before quoting, including turndown, load swings, and the room. Steam properties from standard steam tables. NOx limits are for natural gas, corrected to 3% O2, as of October 2026; South Coast AQMD is amending Rules 1146 and 1146.1. The rule follows each boiler's nameplate rated heat input.