About HomeSizer

HomeSizer (homesizer.elggum.com) is a small set of free calculators for sizing home equipment in the United States: septic tanks, well pumps, water heaters, generators, wire and air conditioners. Every calculation runs in your browser; nothing you type is sent to a server.

Editorial principles

• Numbers come only from published sources: state regulations, the National Electrical Code, U.S. government agencies, university extension services and manufacturer sizing guides.
• Each value is cross-checked against at least two sources. If a figure can't be verified, it is left out.
• Each page shows its formula, a worked example, its assumptions and a "Last updated" date.
• We are not a substitute for an engineer, licensed contractor or code official.

Found an error or a rule that changed? Let us know.

All sources

1. New York State Department of Health: 10 NYCRR Appendix 75-A, Wastewater Treatment Standards – Individual Household Systems (75-A.6 Septic tanks)
2. Maryland Division of State Documents: COMAR 26.04.02.05 – Septic tank design and construction
3. Indiana Department of Health: 410 IAC 6-8.3 Residential Onsite Sewage Systems (Rule 6-8.3-60, Septic tank capacity)
4. Missouri Code of State Regulations (via Cornell LII): 19 CSR 20-3.060 Minimum Construction Standards for Onsite Sewage Disposal Systems
5. University of Missouri Extension: EQ401 – Septic Tank/Absorption Field Systems: A Homeowner's Guide
6. Cornell Cooperative Extension: Your Septic System: Building & Remodeling
7. U.S. EPA: How Your Septic System Works
8. Goulds Water Technology (Xylem): Water Products Technical Manual (TTECHWP)
9. University of Missouri Extension: G1801 – Private Water Systems: Pumps and Pressure Tanks
10. Grundfos / BC Ground Water Association: Submersible Wells & Pumps (training presentation)
11. The Engineering ToolBox: Pumps – Power Calculator
12. U.S. Department of Energy: Sizing a New Water Heater (Energy Saver guide, archived PDF)
13. PNNL Building America Solution Center: Sizing a New Water Heater
14. AHRI: Water Heater Sizing Worksheet
15. ACEEE (smarterhouse.org): Replacing Your Water Heater
16. Natural Resources Canada: ENERGY STAR Water Heater Guide
17. U.S. DOE Building America: Measure Guideline: Tankless Water Heaters
18. U.S. EPA WaterSense: WaterSense Specification for Showerheads
19. U.S. EPA WaterSense: WaterSense Specification for Lavatory Faucets
20. U.S. Energy Information Administration: British thermal units (Btu)
21. U.S. Geological Survey: Water Density
22. Generac: What Size Generator Do I Need?
23. Briggs & Stratton: Wattage Worksheet
24. Champion Power Equipment: Generator Wattage Chart
25. NCCER: Electrical Formula Sheet
26. IAEI Magazine: Voltage Drop Formulas
27. IAEI Magazine: Voltage Drop Calculations
28. NEC Mastery: Voltage Drop – Quick Reference
29. NFPA 70 (NEC 2017) via course reprint: Chapter 9, Table 8 – Conductor Properties
30. VoltDropCalc: NEC Chapter 9 Table 8
31. NECTables: NEC Table 310.16 Ampacity
32. Omni Cable: NEC Ampacity Data (Table 310.16)
33. ENERGY STAR (EPA): Room Air Conditioner sizing chart
34. Natural Resources Canada: ENERGY STAR room air conditioners infographic (sizing chart)
35. GE Appliances: Room Air Conditioner Buying Guide
36. ASHRAE Terminology: Ton of refrigeration
37. ACHR News: Understanding What a Cooling Ton Means
38. ENERGY STAR (EPA): Ask the Experts: How to choose the right-sized window AC
39. Missouri Dept. of Health & Senior Services: Onsite Wastewater System Owner's Manual
40. ACCA: Manual J – Residential Load Calculation