Water Heater Sizing Calculator
Calculate tank size, BTU input, and recovery rate requirements
Household Information
Hot Water Fixtures
Water Temperatures
Water Heater Requirements
Recommended Tank Size
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BTU Input Required
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First Hour Rating (FHR)
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Recovery Rate Needed
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Peak Hour Demand
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Temperature Rise
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Selection Tip: Choose a water heater with FHR matching or exceeding your peak demand. Look for the EnergyGuide label.
Recovery Rate by Fuel Type
| Fuel Type | Efficiency | GPH/40K BTU |
|---|---|---|
| Natural Gas | 80-95% | 40-45 |
| Propane | 80-95% | 38-43 |
| Electric | 95-100% | 18-21 |
| Oil | 80-90% | 50-55 |
BTU Calculation Formula
BTU/hr = GPH × 8.33 × ΔT × (1/η)
GPH = Gallons per hour recovery
8.33 = Weight of water (lbs/gal)
ΔT = Temperature rise (°F)
η = Heater efficiency
Residential Tank Size Guidelines
| Household Size | Bathrooms | Gas Tank | Electric Tank | FHR Needed |
|---|---|---|---|---|
| 1-2 people | 1 | 30-40 gal | 40-50 gal | 30-40 gal |
| 2-3 people | 1-2 | 40-50 gal | 50-60 gal | 40-50 gal |
| 3-4 people | 2 | 50-60 gal | 60-80 gal | 50-60 gal |
| 4-5 people | 2-3 | 60-75 gal | 80+ gal | 60-80 gal |
| 5+ people | 3+ | 75+ gal | 80+ or 2 units | 80+ gal |