The RV furnace typically runs on propane for heat, while the blower and control electronics use 12-volt power. When choosing a generator to support an RV furnace, focus on supplying enough 12V power for the blower and controls and enough 120V capacity to keep the RV’s converter and battery charging system active. The exact size depends on your furnace model, the converter rating, and other loads you plan to run while camping. This guide outlines how to estimate the right generator size for reliable operation without overloading the system.
How RV Furnaces Work And Power Needs
Most RV furnaces heat with propane and use a small 12-volt DC blower to circulate warm air. The thermostat and gas valve also run on low-voltage power. The electrical draw of the furnace itself is relatively modest, but it has a startup surge as the blower motor starts. Typical continuous draw is around 1.5 to 2.5 amps at 12V (roughly 20 to 30 watts), with startup surges in the 4 to 6 amp range (about 50 to 70 watts) for a split second. The heater’s heat source remains propane; the 12V system mainly powers the blower, ignition, and control circuitry.
In practice, the generator’s role is to provide enough 120V AC power to run the RV’s converter and keep the battery charged, so the 12V system has a reliable supply. This means the generator’s AC output must support the RV’s battery charger, along with any other 120V loads you intend to run. If the battery is low, the converter can demand more current, increasing the generator’s load. Plan for a buffer to accommodate charging fluctuations and blower startup.
Estimating Your Generator Size
To size a generator for running the RV furnace, start by identifying three numbers: the furnace blower current at 12V, the highest current the RV’s battery converter will draw, and any additional 120V loads you expect to run. Add these values and include a safety buffer to handle startup surges.
- Furnace blower current: Check the furnace label or manual. Expect roughly 1.5–2.5 A continuous (about 20–30 W). Prepare for a startup surge of 4–6 A (about 50–70 W) for a brief moment.
- Battery converter rating: Many RV converters are in the 40–60 A range at 12V. That translates to about 480–720 W of DC charging capacity; the AC input from 120V will be similar in total power, plus efficiency losses. Plan for roughly 700–900 W of AC load when charging at full tilt.
- Other loads: Add lighting (LEDs are low power), a water pump, or a small appliance. A typical RV fridge on AC may draw 100–300 W, depending on cycle and model. Small devices (phones, chargers) add only tens of watts.
Example calculation: If the furnace blower runs at about 2 A (24 W) and the converter is charging up to 60 A at 12V (roughly 720 W DC output, with 800–900 W AC input), plus lights and pump totaling around 60 W, the base load is near 880–940 W. With a 20–25% headroom for surges and efficiency losses, a generator in the 1100–1200 W range is often sufficient for many setups. If you anticipate higher AC loads, plan for 1500–2000 W to be safe.
Practical Generator Sizes For Common Scenarios
Choosing a generator depends on how many loads you plan to run along with the RV furnace. The following ranges reflect typical scenarios for a propane furnace powered by a 12V blower.
- Furnace only + basic lighting: 1000–1500 W. A small, quiet portable generator in this range can keep the battery charging active while the furnace runs and power a few LED lights.
- Furnace + battery charger + essential appliances: 1500–2000 W. If you run the converter at higher charging rate and have a few additional devices (e.g., water pump, basic outlets), this range provides comfortable headroom.
- Furnace + charging + moderate appliances (fridge on AC, small AC devices): 2000–3000 W. More headroom allows continuous charging plus fridge cycling and small electronics without tripping.
- Furnace + full loads (air conditioner, microwave, etc.): 3000–4500+ W. Running an air conditioner or other high-draw appliances alongside the furnace requires a larger generator to prevent overloads.
Note: If the RV uses a 30–50 A service, large electrical loads can dramatically increase required wattage. In those cases, the generator choice should align with the combined peak loads and not just the furnace alone.
Inverter Generators And Efficient Operation
Inverter generators are a popular choice for RVs because they deliver cleaner power at various loads, run more quietly, and adjust output to match demand. When sizing an inverter generator for an RV furnace, ensure the continuous wattage rating comfortably exceeds the expected load including the furnace blower surge and converter charging. For example, a 1500–2000 W inverter generator typically accommodates a furnace plus moderate charging and other small loads, with the added benefit of smoother operation and better fuel efficiency.
Safety, Installation, And Best Practices
Safety is essential when using any generator around an RV. Place the generator outdoors on a flat, ventilated surface to provide adequate airflow and avoid carbon monoxide buildup. Use outdoor-rated cords with appropriate gauge to minimize voltage drop, and never backfeed power through an RV’s outlets or shore power inlet. Regularly inspect the generator’s oil, air filter, and spark plug. When starting the furnace, ensure the battery is charged; a weak battery can prevent the blower from starting, even if the generator is running. Keep fuel containers away from ignition sources and store fuel in approved containers.
Practical Steps To Determine Your Needs
Follow these steps to finalize your generator choice:
- Identify the furnace blower current and startup surge from the furnace label or manual.
- Check your RV’s converter rating and estimate AC input during charging.
- List other loads you plan to run (lights, water pump, fridge, small appliances).
- Compute total wattage and add 20–25% headroom for surges and efficiency losses.
- Choose a generator with a continuous wattage rating at or above the calculated total, preferring models in the 1200–2000 W range for most setups.
By aligning the generator size with the furnace’s electrical needs and the RV’s charging requirements, campers can maintain comfortable heating without overloading the electrical system. Always consult the specific furnace and converter manuals for exact current ratings and follow safety guidelines for outdoor operation.