Propane planning
Estimate how many days your propane capacity supports furnace heat, fridge operation, hot water, cooking, and other BTU loads before refill margin gets thin.
Quick propane read
With 34 usable pounds after reserve, this setup uses about 4.31 lb per day and lasts roughly 7.9 days on the entered assumptions.
Estimated runtime
Plan a refill around day 6.3
Daily propane
1.02 gal per day
Furnace share
72k BTU of 93k BTU daily demand
Runtime math does not replace propane safety checks. Verify regulator condition, leak checks, ventilation, appliance service, and carbon-monoxide alarms before relying on propane heat.
Start over
This calculator stores inputs locally in this browser. Clear saved inputs when stale values are getting in the way.
Propane duration calculator
Enter propane capacity in pounds, then estimate the daily BTU demand from the furnace and other propane appliances. The calculator converts that into pounds, gallons, and a conservative refill planning point.
Propane runtime estimate
With 34 usable pounds after reserve, this setup uses about 4.31 lb per day and lasts roughly 7.9 days on the entered assumptions.
Estimated runtime
7.9 days
Plan a refill around day 6.3 with the entered reserve
Daily propane
4.31 lb
1.02 gal per day at the entered BTU load
Usable propane
34.0 lb
8.00 gal after 15% reserve
Furnace share
77%
72k BTU of 93k BTU daily demand
Daily BTU breakdown
Furnace
72k BTU
Fridge
10k BTU
Water heater
8k BTU
Cooking + other
3k BTU
Watch-outs
Propane use changes quickly with wind, insulation, thermostat setting, altitude, appliance condition, and how often doors open.
A 20 lb cylinder means about 20 lb of propane when filled, not 20 gallons. This calculator uses pounds as the capacity input.
The furnace dominates this estimate. Cold snaps, wind, and slide-outs can shorten runtime faster than mild-weather averages suggest.
Recommended next move
Build the plan around colder-than-average nights: carry more propane, reduce thermostat demand, skirt or insulate weak spots, or shorten the stay.
Why this exists
Solar and battery calculators do not show how fast the furnace can burn through cylinders during cold nights. This calculator keeps BTU demand visible so you can compare propane, water, and power limits before committing to a stay.
Use this with
Stay length calculator
Use this when propane is only one possible limiter and you need to compare power, water, and waste too.
Open next stepWater calculator
Use this when the same cold-weather trip also depends on tank size and conservation habits.
Open next stepBoondocking duration guide
Use this for the broader stay-length planning logic beyond a single fuel source.
Open next stepGenerator runtime calculator
Use this if propane heat and generator charging both matter for a cold off-grid stay.
Open next stepTool notes
The output is a stay-duration planning estimate. It does not replace propane safety checks, appliance maintenance, leak testing, ventilation, or manufacturer guidance.
Furnace rating is multiplied by the hours it is available and the duty-cycle percentage, because the burner does not usually fire continuously.
Total daily BTU demand is divided by roughly 21,600 BTU per pound of propane to estimate daily pounds and gallons.
Tank capacity is reduced by the reserve percentage before the calculator estimates runtime and a conservative refill-planning point.
Avoid these traps
Portable cylinders are labeled by pounds of propane, not gallons. Two 20 lb cylinders should be entered as 40 lb of propane capacity.
Furnace use can double when wind, slide-outs, poor insulation, or a lower overnight temperature hit the rig. Winter planning needs margin.
An absorption fridge, water heater, stove, oven, catalytic heater, or propane generator can quietly shorten the stay even when the furnace math looks fine.
Treat the calculator result as a planning range, then verify the relevant manufacturer guidance, safety limits, installation requirements, and local rules before changing the rig.See assumptions
Gear to compare after the math
These handoffs match the calculator family, not a one-click prescription. Verify fit, specs, clearances, and install limits before buying.
SOK SK12V100P 12V 100Ah LiFePO4 Battery
Best for
Budget lithium builds after a smaller bank result
A common 100Ah building block when the calculator result still fits a straightforward 12V lithium bank.
Current listing
SOK SK12V100P 12V 100Ah LiFePO4 Battery at SOK.
Victron SmartShunt 500A/50mV
Best for
Making battery runtime visible instead of guessed
A shunt-based monitor is the usual next buy when the calculator result depends on real state-of-charge tracking.
Current listing
Victron SmartShunt 500A/50mV at Victron.
Victron Orion XS 12/12-50A DC-DC Battery Charger
Best for
Improving recharge support for larger daily loads
Use this class of DC-DC charger when the battery answer only works if drive-day recovery is part of the plan.
Current listing
Victron Orion XS 12/12-50A DC-DC Battery Charger at Victron.
Frequently asked
Enter the rated propane capacity in pounds. Two 20 lb cylinders are 40 lb, two 30 lb cylinders are 60 lb, and a larger onboard tank should be converted to pounds if the gauge is listed in gallons.
Use the share of the heating window when the burner is actually firing. If the furnace can run for eight overnight hours but cycles on about a third of the time, use roughly 33%.
The furnace is usually the largest propane load in cold weather. Wind, poor skirting, open underbellies, slide-outs, and frequent door openings can raise duty cycle quickly.
No. It is a runtime estimate. Follow manufacturer instructions for propane storage, regulator condition, leak checks, ventilation, carbon-monoxide alarms, and appliance service.