Affiliate disclosure: We earn a commission when you buy through links on this page, including as an Amazon Associate and eBay Partner Network affiliate, at no extra cost to you. We don't invent test results or prices: price tiers ($ to $$$$) are relative, so always check the current listing.
Key takeaways
- RV furnaces use propane for heat and 12V power for the blower, igniter and controls. The blower is the part that drains your battery.
- Manufacturer service manuals list 12V draws from roughly 3 amps on small units up to about 11 to 12.5 amps on the largest models.
- Overnight use depends on the duty cycle: how many hours the blower actually runs, not how many hours the thermostat is on.
- The formula is simple: amps × hours of blower run time = amp-hours. Measure with a shunt monitor for real numbers.
- Cutting furnace run time with insulation, a lower night setting and warm bedding often saves more than adding solar.
How an RV furnace uses battery power
A typical RV furnace is a forced-air propane unit. When the thermostat calls for heat, a 12V blower starts first to purge the combustion chamber, the control board lights the burner, and the blower then pushes air across the heat exchanger and through the ducts. When the thermostat is satisfied, the burner shuts off and the blower keeps running briefly to cool down.
So the propane makes the heat, but the battery powers the blower every minute the furnace cycles. On a cold night, that can add up to more than your fridge, lights and phone charging combined.
This guide covers the power side. If your furnace isn't lighting, is short-cycling or blowing cold air, that's a repair question. See RVgear's RV furnace troubleshooting guide.
What manufacturers list for blower draw
Blower draw varies by model, size and motor. Here's what the two biggest RV furnace makers publish in their service manuals.
| Source | Model family | Listed 12V draw |
|---|---|---|
| Suburban service and training manual | NT series (12,000 to 40,000 BTU) | About 2.8 to 9.5 A, rising with size |
| Suburban service and training manual | SF series (20,000 to 40,000 BTU) | About 6.5 to 11.5 A, depending on size and motor |
| Atwood furnace service manual | 8500 series | 4.6 to 9.8 A, depending on model |
| Atwood furnace service manual | AFS series | About 3.4 to 4.8 A |
| Atwood furnace service manual | AFM series | 4.3 to 11.1 A, depending on model |
Across these lines, the listed range runs from roughly 3 amps on small furnaces to around 11 to 12.5 amps on the largest DC models. Most mid-size ducted furnaces in travel trailers and fifth wheels fall somewhere in the middle.
Measuring your furnace's draw
The label gives you a rated number. Measuring gives you the real one, which matters because older motors, dirty blower wheels and low voltage can all change it.
With a shunt battery monitor
- Turn off other large loads, and note the monitor's current reading.
- Turn the thermostat up so the furnace starts.
- Wait until the burner lights and the blower is at full speed.
- Read the current again. The difference is roughly the furnace draw.
A shunt monitor also logs overnight amp-hours, which is the best way to see the real total. See best RV battery monitors.
With a DC clamp meter
Clamp a DC-capable clamp meter around the furnace's positive supply wire, if it's accessible, or around the battery's main cable while other loads are off. See our clamp meter guide. Don't open panels or disconnect wiring you're not comfortable with.
The overnight amp-hour math
The furnace doesn't run the whole night. It cycles. What matters is total blower run time.
Worked example 1: mild desert night
Say your furnace measures 7 A (a clearly labeled example value), you keep it on for 10 hours overnight, and on a mild night the blower runs about 30 percent of the time.
- Run time: 10 × 0.30 = 3 hours
- Overnight use: 7 × 3 = 21 Ah
Worked example 2: cold night, same furnace
On a colder, windier night, the blower might run 60 percent of the time.
- Run time: 10 × 0.60 = 6 hours
- Overnight use: 7 × 6 = 42 Ah
Worked example 3: a larger furnace on a cold night
A bigger furnace measuring 10 A (example value) at the same 60 percent duty cycle:
- Run time: 6 hours
- Overnight use: 10 × 6 = 60 Ah
The duty cycle depends on outside temperature, wind, insulation, thermostat setting and furnace size. That's why measured overnight numbers are so much more useful than estimates.
| Scenario | Example draw | Duty cycle | Example overnight Ah |
|---|---|---|---|
| Mild night, mid-size furnace | 7 A | 30% | 21 Ah |
| Cold night, mid-size furnace | 7 A | 60% | 42 Ah |
| Cold night, large furnace | 10 A | 60% | 60 Ah |
Sizing solar to recover furnace use
Once you know overnight Ah, you can size solar to put it back the next day.
The 0.77 is a planning allowance for controller, wiring and heat losses, not a measured figure for your rig.
Using worked example 2 (42 Ah) and 4 winter peak sun hours (an example; look up your location in NREL's PVWatts):
- Energy: 42 × 12 = 504 Wh
- Solar: 504 ÷ (4 × 0.77) ≈ 164 W
That's just to cover the furnace. Add your fridge, lights, electronics and phantom loads to size the whole system. Our snowbird RV solar guide walks through a full winter load list, and RV battery bank sizing calculator covers days of autonomy.
Bluetti power stations
All-in-one LiFePO4 power stations with built-in inverter, charger and solar input. Compare current models and bundles on Bluetti's own store.
See Bluetti modelsRenogy components
Panels, MPPT charge controllers, DC-DC chargers and lithium batteries for custom builds. Check specs and current kits on Renogy's store.
Shop Renogy gearWays to cut furnace battery use
The cheapest amp-hour is the one you don't use.
- Lower the overnight setting and use warm bedding or a 12V heated blanket. See best 12V appliances for RVs.
- Insulate windows and roof vents with reflective covers or vent pillows.
- Close off unused areas so the furnace heats less space, as long as you don't block returns or ducts the manual requires open.
- Keep the blower and returns clean, since a dirty blower wheel works harder. Service is covered by RVgear's furnace troubleshooting guide.
- Consider alternative heat sources carefully. RVgear compares propane vs electric heat in RVs, and we compare RV furnace vs diesel heater power draw.
Low voltage and furnace problems
Furnaces can behave badly on low battery voltage. The blower may spin slower, and some safety switches may not close, so the burner doesn't light. If your furnace acts up late at night, check battery voltage first. A healthy lithium bank that holds voltage under load can help. See LiFePO4 vs AGM for RV solar.
Practical steps before winter
- Find your furnace model and its listed amp draw on the data plate or in the manual.
- Measure the real draw with a shunt monitor or DC clamp meter.
- Log one cold night of use to learn your real overnight Ah.
- Size your battery bank to cover that plus your other loads, with days of autonomy.
- Size solar to recover it on a short winter day, or plan backup charging.
- Insulate and lower the thermostat before you add hardware.
Frequently asked questions
How many amps does an RV furnace draw?
It depends on the model. Suburban and Atwood service manuals list 12V draws from roughly 3 amps on small units to about 11 to 12.5 amps on the largest DC models. Check your furnace's data plate or measure it with a battery monitor.
How much battery does an RV furnace use overnight?
Multiply the blower's amp draw by the hours it actually runs. For example, a 7 A blower running 6 hours of a 10-hour night uses about 42 Ah. Your real number depends on temperature, wind, insulation and thermostat setting.
Can solar keep up with an RV furnace?
Often, yes, if the array is sized for winter sun and the battery bank covers the overnight draw. Convert overnight Ah to watt-hours, then divide by winter peak sun hours times a planning efficiency to estimate the solar needed.
Why won't my RV furnace light when the battery is low?
Low voltage can slow the blower and keep safety switches from closing, so the burner doesn't light. Check battery voltage first. For repair steps, see RVgear's furnace troubleshooting guide.
Does the RV furnace use propane or battery?
Both. Propane produces the heat, while the 12V battery runs the blower, igniter and control board.