DOE EnergyGuide & IPC Chapter 518 Verified Engineering Schedules
Water Heater Sizing & Capacity Directory
Deterministic engineering schedules for residential storage tanks (First Hour Rating - FHR) and tankless on-demand hot water systems. Look up exact gallon capacities, peak demand GPM, burner BTU ratings, and electrical panel requirements for your household size and bathroom count.
Storage Tank & Hybrid Heat Pump Sizing (DOE First Hour Rating)
Water Heater Sizing for Family of 2 (30–40 Gallons)
Target Tank: 40 Gallons (FHR: 50 GPH)
2 OccupantsEst. Mat: $1108
Water Heater Sizing for Family of 3 (40–50 Gallons)
Target Tank: 50 Gallons (FHR: 65 GPH)
3 OccupantsEst. Mat: $1108
Water Heater Sizing for Family of 4 (50–60 Gallons)
Target Tank: 80 Gallons (FHR: 110 GPH)
4 OccupantsEst. Mat: $1508
Water Heater Sizing for Family of 5 (60–75 Gallons)
Target Tank: 80 Gallons (FHR: 140 GPH)
5 OccupantsEst. Mat: $1508
Water Heater Sizing for Family of 6 or More (75–80+ Gallons)
Target Tank: 80 Gallons (FHR: 165 GPH)
6 OccupantsEst. Mat: $1508
40-Gallon Water Heater Sizing & Capacity Guide
Target Tank: 50 Gallons (FHR: 60 GPH)
2 OccupantsEst. Mat: $860
50-Gallon Water Heater Capacity & Shower Rating
Target Tank: 65 Gallons (FHR: 80 GPH)
4 OccupantsEst. Mat: $1508
50 Gallon vs 40 Gallon Water Heater Sizing Comparison
Target Tank: 65 Gallons (FHR: 80 GPH)
3 OccupantsEst. Mat: $1508
Hybrid Heat Pump Water Heater Sizing for Family of 4 (65–80 Gal)
Target Tank: 80 Gallons (FHR: 110 GPH)
4 OccupantsEst. Mat: $2660
Tankless On-Demand Sizing (GPM, Delta-T, Gas BTU & Electric kW)
Tankless Water Heater Sizing for 1 Bathroom (2.5–3.5 GPM)
Flow Rate: 3.5 GPM (@ +65°F Rise)
1 Full Bathroom120k BTU/hr
Tankless Water Heater Sizing for 2 Bathrooms (5.0–5.5 GPM)
Flow Rate: 7 GPM (@ +65°F Rise)
2 Full Bathrooms240k BTU/hr
Tankless Water Heater Sizing for 2.5 Bathrooms (6.0–6.5 GPM)
Flow Rate: 10 GPM (@ +65°F Rise)
2.5 Bathrooms (2 Full + 1 Powder)345k BTU/hr
Tankless Water Heater Sizing for 3 Bathrooms (7.5–8.5 GPM)
Flow Rate: 12.5 GPM (@ +65°F Rise)
3 Full Bathrooms430k BTU/hr
Tankless Water Heater Sizing for 4 Bathrooms (9.5–11.0 GPM)
Flow Rate: 15.5 GPM (@ +65°F Rise)
4 Full Bathrooms535k BTU/hr
Cold Climate Tankless Water Heater Sizing (Zone 1 & 2 Groundwater)
Flow Rate: 7 GPM (@ +80°F Rise)
2 Bathrooms in Cold Region295k BTU/hr
Warm Southern Climate Tankless Water Heater Sizing (Zone 4 & 5)
Flow Rate: 8 GPM (@ +48°F Rise)
2.5 Bathrooms in Warm Region205k BTU/hr
Electric Tankless Water Heater Electrical & Amperage Sizing
Flow Rate: 5.5 GPM (@ +65°F Rise)
1.5-2 Bathrooms190k BTU/hr
Gas Tankless Water Heater BTU Sizing & Gas Line Sizing
Flow Rate: 9.5 GPM (@ +65°F Rise)
2.5-3 Bathrooms325k BTU/hr
Code Compliance Note
All calculations adhere to the US Department of Energy (DOE) Sizing Standards, International Plumbing Code (IPC Section 504 & 607), and ASPE Chapter 5 domestic water heating guidelines. Local municipal codes and altitude deratings may require additional capacity adjustments.