The RV furnace typically uses propane for heat but requires electricity for the blower and controls; choosing the right generator size ensures reliable starts, continuous blower operation, and the ability to run other RV loads. This guide explains how to calculate starting and running watts, compares inverter and conventional generators, and recommends practical generator sizes based on common RV furnace power draws and additional appliances.
| Furnace Blower Type | Approx Running Watts | Typical Starting Surge | Recommended Minimum Generator Size |
|---|---|---|---|
| Small Blower (Low CFM) | 200–350 W | 400–800 W | 2000 W |
| Medium Blower (Most RVs) | 350–600 W | 700–1,200 W | 2000–3000 W |
| Large Blower / Older Units | 600–900 W | 1,200–1,800 W | 3,000–4,500 W |
| Furnace Plus Microwave/AC/Fridge | varies | high surge | 3,500–5,500+ W |
How RV Furnaces Use Electricity
Most RV furnaces burn propane to produce heat; electricity powers the thermostat, control board and the blower motor that moves warm air through the ducting. The blower is the primary electrical load and is responsible for both continuous running watts and the higher startup surge when the motor engages.
Typical Power Draws And Start-Up Surge
Typical modern RV furnace blowers draw between 200 and 900 watts running, depending on blower size and speed setting. Start-up surge can be 2–3 times the running current, so a 500 W running blower may need 1,000–1,500 W at startup.
Why Start-Up Surge Matters For Generator Sizing
Generators have two ratings: continuous (running) watts and peak (starting) watts. If a generator cannot provide sufficient surge, the blower may fail to start, the generator could trip its breaker, or sensitive electronics could experience voltage dips. Proper sizing must cover both running and surge requirements.
Choosing The Right Generator Size
To select an appropriate generator, add the running watts of all loads that might run simultaneously and ensure the generator’s surge rating covers the highest startup requirement. For an RV furnace alone, a well-maintained 2,000–3,000 watt generator is often sufficient. When the furnace will run with other appliances, step up the size accordingly.
Common Recommendations
- 2000–2200W Inverter Generators: Often adequate for furnace blower only and small electronics. Good for lighter boondocking needs and quiet operation.
- 3000–3500W Generators: Best balance for furnaces plus a refrigerator, microwave (limited use), and charging devices.
- 4000–5500W Generators: Recommended when running roof AC, microwave simultaneously, or powering multiple high-draw appliances.
Example Load Scenarios And Generator Choices
These examples assume a furnace blower running watt estimate plus typical RV appliance draws. Exact wattages vary by model—always check appliance nameplates or manuals.
| Scenario | Estimated Running Watts | Estimated Starting Surge | Recommended Generator |
|---|---|---|---|
| Furnace Only (Medium Blower) | 400 W | 900 W | 2000–2200 W inverter |
| Furnace + Refrigerator (12V Compressor via converter) | 400–800 W | 900–1500 W | 3000 W |
| Furnace + Microwave (short use) | 400 W + 1000–1200 W | 900–2000 W | 3500–4500 W |
| Furnace + Roof AC | 400 W + 1500–1800 W | 900–3000 W | 4000–5500+ W |
Inverter Generators Versus Conventional Generators
Inverter generators deliver clean, stable power with low total harmonic distortion (THD), making them ideal for sensitive electronics and modern RV systems. They are quieter and more fuel-efficient at partial loads. Conventional portable generators often provide higher surge capacity for the price but can be louder and less fuel-efficient.
Why Inverter Generators Are Popular For RV Use
Inverter units like the Honda EU2200i or Yamaha models are popular because they are lightweight, quiet, and produce stable sine-wave power suitable for thermostats, TVs, and charging systems. For many RVers, a 2000–3000 W inverter is adequate for furnace operation plus basic needs.
Surge Capacity And Generator Ratings Explained
Generator specifications list two numbers: running (continuous) watts and starting (surge) watts. The starting watt rating indicates how much short-term surge power the generator can provide to start motors and compressors. Always ensure the generator’s starting watts exceed the highest single equipment surge requirement in the load.
How To Calculate Exact Generator Requirements
- List every electrical appliance that may run simultaneously (furnace blower, fridge, lights, microwave, water pump, inverter loads).
- Find running and starting watts for each item (manufacturer spec sheet or nameplate).
- Add all running watts to get total continuous load.
- Identify the largest single starting surge and ensure the generator’s peak rating covers it.
- Add a 20–25% buffer for safety and future flexibility.
Practical Steps Before Purchasing
- Measure actual watt draws with a clamp meter or inline watt meter if unsure about estimates.
- Check the furnace manual for blower motor amps and convert to watts (Watts = Volts × Amps).
- Decide whether quiet operation and low THD are priorities (favor inverters) or whether raw surge capacity and price are more important.
Recommended Generator Models For RV Furnaces
Several popular models are reliable choices depending on needs: Honda EU2200i (2200W inverter) for quiet furnace-only use; Champion 2500–3500W series for mid-range budgets; Westinghouse 3000–4200W models for higher surge needs; Generac or Champion 4000–5500W conventional units when running AC and microwave together. Select models with CO shutdown features for safety.
Safety And Installation Considerations
Never run a generator inside the RV or an enclosed area; carbon monoxide is deadly. Use an RV-grade shore power inlet or portable power cord rated for the generator. Install a CO detector and ensure shore power transfer switches or manual transfer procedures prevent backfeeding into campground wiring.
Fuel Type, Run Time, And Portability
Consider fuel availability and run time. Gasoline is common for portable generators but has limited shelf life; propane or dual-fuel models offer longer storage life and convenience for RVers who already carry propane. Inverter models typically provide better fuel efficiency and quieter operation for boondocking.
Maintaining Reliable Generator Performance
Routine maintenance extends generator life and improves reliability: perform oil changes, replace air filters, run the generator monthly under load, and use fresh fuel or fuel stabilizer. Maintain battery health if the RV uses an electric start, and keep spark plugs and valves in good condition.
When To Consider An Inverter/Hybrid Power Setup
For silent overnight operation during cold nights, combining a small inverter generator with a lithium battery bank and inverter can allow the furnace blower to run off stored DC power, reducing generator runtime. This setup requires an inverter sized for the blower surge and a battery/inverter system capable of motor starting or peak-shaving.
Checklist Before Running The Furnace On A Generator
- Verify generator running and starting watt ratings against calculated loads.
- Ensure proper ventilation and CO detectors are functioning.
- Use correct-length and rated power cords and an RV transfer device.
- Start high-surge items first if possible to avoid cumulative peak demands.
- Keep fuel on hand and monitor oil and coolant levels.
Troubleshooting Common Issues
If the furnace blower fails to start when connected to the generator, check for low voltage or insufficient surge capacity; try reducing simultaneous loads or start the blower alone to verify if the generator handles its startup. If electronics flicker or reset, consider an inverter generator with lower THD or upgraded capacity.
Final Sizing Guidelines
For most RVers wanting dependable furnace operation with room for modest extras, a 3,000–3,500 watt generator is a practical compromise. For minimal setups or silent boondocking where only the furnace blower and a few devices run, a 2,000–2,200 watt inverter may suffice. For running AC or multiple high-draw appliances, step up to 4,000–5,500+ watts.
Choosing the right generator protects comfort and equipment, minimizes nuisance trips, and ensures safe, reliable operation of the RV furnace and other critical systems while off-grid.