A power outage can disrupt your daily life, especially in a duplex house where two families may depend on one system. Choosing the right generator size is crucial to ensure comfort, safety, and convenience during emergencies. Whether you’re preparing for grid instability, natural disasters, or remote living, understanding how to properly size a generator for a duplex home is essential.
Generator Size Calculator for Duplex House
Enter estimated wattage per category for each unit. The calculator sums all, adds a 20% margin, and recommends minimum generator size in kW.
In this comprehensive guide, you’ll learn:
- How to calculate generator size
- Average generator sizes for duplexes
- Power requirements for essential and luxury appliances
- Types of generators suitable for duplex homes
- Installation and safety tips
- Cost and efficiency considerations
1. Understanding Your Duplex Power Needs
A duplex house typically consists of two residential units under one roof. Each may have its own kitchen, bathroom, HVAC system, and electrical load. So, when sizing a generator, you’re essentially planning for two households.
Typical Power Loads for a Duplex Home
| Appliance/Equipment | Power (Wattage) Range |
|---|---|
| Refrigerator (per unit) | 600 – 800 W |
| Microwave (per unit) | 800 – 1,200 W |
| Electric Stove (per unit) | 1,500 – 3,000 W |
| Central AC (per unit) | 3,000 – 5,000 W |
| Washing Machine (per unit) | 500 – 1,000 W |
| Water Heater (electric) | 3,000 – 4,500 W |
| Lights (per unit) | 300 – 600 W |
| TV and Entertainment (per unit) | 200 – 500 W |
| Laptop & Internet (per unit) | 100 – 300 W |
| Sump Pump | 750 – 1,500 W |
| Well Pump (if present) | 1,000 – 2,000 W |
Multiply by two for a full duplex estimate. Also, keep in mind surge power – when devices start up, they consume more power momentarily.
2. How to Calculate Generator Size for a Duplex
Step-by-Step Process:
- List essential appliances in both units.
- Add wattages for running power.
- Account for surge watts (especially for refrigerators, AC, and pumps).
- Add a 20% buffer for safety and future expansion.
Example Load Calculation
| Item | Quantity | Running Watts | Surge Watts |
|---|---|---|---|
| Refrigerator | 2 | 1,600 W | 2,000 W |
| Microwave | 2 | 2,400 W | — |
| Electric Stove | 2 | 6,000 W | — |
| Central AC (2 units) | 2 | 8,000 W | 10,000 W |
| Washing Machine | 2 | 2,000 W | 2,400 W |
| Lighting | — | 1,000 W | — |
| Water Heater | 2 | 9,000 W | — |
| Misc. electronics | — | 1,000 W | — |
Total Running Watts: ~31,000 W
Total Surge Watts: ~34,000 – 36,000 W
Final Generator Size:
- Minimum Recommended: 36 – 40 kW generator
- If only powering essentials: 20 – 25 kW may suffice
3. Generator Sizes by Duplex Type
| Duplex Type | Area (sq. ft.) | Suggested Generator Size |
|---|---|---|
| Small duplex (2x 1 bed, 1 bath) | 1,500 – 2,000 | 15 – 20 kW |
| Mid-size duplex (2x 2–3 bed units) | 2,000 – 3,000 | 20 – 30 kW |
| Large duplex (luxury or HVAC-heavy) | 3,000+ | 30 – 40+ kW |
4. Types of Generators for Duplex Homes
1. Portable Generators
- Pros: Affordable, flexible
- Cons: Limited power, manual operation
- Use Case: Temporary or minimal backup
2. Standby Generators (Whole-House)
- Pros: Automatic, powerful, supports full duplex
- Cons: Expensive, requires installation
- Use Case: Seamless power for both units
3. Inverter Generators
- Pros: Quiet, fuel-efficient, clean power
- Cons: Low output, best for sensitive electronics
- Use Case: Supplementary power or for partial loads
| Generator Type | Power Range | Cost Range | Best For |
|---|---|---|---|
| Portable | 2 – 10 kW | $500 – $3,000 | Small essentials |
| Inverter | 2 – 7.5 kW | $800 – $3,000 | Electronics only |
| Standby Generator | 15 – 50+ kW | $3,500 – $15,000+ | Full duplex coverage |
5. Fuel Types and Runtime
| Fuel Type | Pros | Cons | Runtime Notes |
|---|---|---|---|
| Gasoline | Widely available | Short shelf life, flammable | 8–12 hours/tank |
| Diesel | Efficient, long-lasting | Noisy, emissions | 12–24 hours/tank |
| Propane (LPG) | Clean-burning, long shelf life | Lower energy density | 8–24 hours/tank (varies) |
| Natural Gas | Unlimited via utility supply | Needs gas line infrastructure | Continuous if piped |
| Solar + Battery | Eco-friendly, silent | Expensive, weather-dependent | Hours to a few days |
For duplexes, propane or natural gas generators are often preferred due to longer runtime and safety.
6. Transfer Switch & Electrical Panel Integration
To integrate a generator safely into your duplex:
- Install a manual or automatic transfer switch for each unit.
- Consider split panels so each unit controls its own circuits.
- Always hire a licensed electrician for installation.
Panel Configuration Tips
| Feature | Recommendation |
|---|---|
| Transfer switch | 200-amp automatic (for whole duplex) |
| Separate circuits per unit | Yes – essential for billing and control |
| Surge protector | Optional but beneficial |
| Generator interlock kit | For portable generator integration |
7. Generator Placement and Noise Considerations
Follow these safety and comfort guidelines:
- Install at least 5 feet away from windows/doors
- Use soundproof enclosures for standby generators
- Ensure ventilation to avoid carbon monoxide buildup
- Avoid placing near flammable materials
| Generator Type | Average Noise (dB) |
|---|---|
| Portable Generator | 70 – 85 dB |
| Inverter Generator | 50 – 65 dB |
| Standby Generator | 65 – 75 dB |
8. Maintenance Requirements
To keep your generator reliable:
| Maintenance Task | Frequency |
|---|---|
| Oil & filter change | Every 100 – 200 hours |
| Air filter replacement | Every 6 months |
| Spark plug replacement | Yearly |
| Battery check | Monthly |
| Load test | Every 6 – 12 months |
For duplex homes, consider signing up for annual service contracts with local professionals.
9. Budget Considerations
| Item | Estimated Cost (USD) |
|---|---|
| 20–30 kW Generator | $4,000 – $10,000 |
| Transfer Switch (Automatic) | $500 – $1,500 |
| Installation & Wiring | $2,000 – $5,000 |
| Concrete Pad/Enclosure | $500 – $1,000 |
| Annual Maintenance (contract) | $300 – $600 |
Total Cost Range: $7,000 – $15,000+
For portable systems: under $3,000 for essentials only
10. Frequently Asked Questions
Q1: Can I use one generator for both units in my duplex?
Yes, but ensure it has enough wattage (30–40 kW typically) and is wired to support both panels safely.
Q2: Is solar backup enough for a duplex?
Solar with battery backup can work for essentials, but full coverage during cloudy days is a challenge unless you invest in a large system.
Q3: Should I install two separate generators?
In rare cases, yes—especially if the duplex units are independently owned or have distinct power needs. Otherwise, one large standby generator is more efficient.
Q4: What if I have gas heating?
If you’re using gas for heating and cooking, your overall electric load is reduced, and a 20 – 25 kW generator may suffice.
Conclusion
Choosing the right generator size for your duplex home depends on your unique layout, appliance needs, and comfort expectations. For full-home backup, a 30 – 40 kW standby generator is often ideal. For essential loads only, a 15 – 25 kW system may suffice. Always work with professionals for sizing and installation.
Summary Table: Generator Sizing for Duplex Homes
| Use Scenario | Recommended Size |
|---|---|
| Essential loads only (2 units) | 15 – 25 kW |
| Full-home power (2 units) | 30 – 40+ kW |
| Portable backup for one unit | 5 – 7.5 kW |
| Shared luxury duplex | 40 – 50+ kW |