Propane Heating Calculator

Propane sizing for planned and backup heat

Estimate room or whole-home propane demand from area, design temperatures, shell quality, appliance efficiency, start fill, and reserve target so runtime reflects the tank you actually have available.

Heating load scales with conditioned area, ceiling height, and indoor to outdoor delta.

Propane use is based on 91,500 BTU per gallon and the selected appliance AFUE.

Runtime honors both start fill percentage and the reserve you plan to keep untouched.

Imperial and metric inputs convert in place without changing the underlying calculation.

📍Preset Heating Scenarios

Reading room profile

This default preset uses a modest conditioned room, an average shell, and a direct-vent stove so you can see how design temperature and reserve target shape burn rate and autonomy.

📏Heating Load Inputs

Condensing and standard furnaces convert more of the fuel into delivered space heat, while room heaters, stoves, and unit heaters trade efficiency for zone-focused deployment.

Unit system

Length, area, and temperature fields convert in place when you switch systems.

Heated area shape

Use the footprint the heater actually supports rather than the full building shell.

Appliance type

Each profile stores a real AFUE or delivered-efficiency assumption in the script.

Length or base (ft)

Rectangle uses length times width. Triangle uses base times height divided by two.

Width (ft)

Use inside conditioned dimensions for the heated footprint.

Diameter (ft)

Circle mode uses pi times radius squared for area.

Triangle height (ft)

Useful for bonus rooms and angled additions.

Custom area (sq ft)

Use this when you already know the conditioned square footage.

Ceiling height (ft)

Load scales from an 8 foot baseline to reflect larger heated volume.

Indoor setpoint (F)

Choose the indoor target you intend to hold during the burn window.

Outdoor design temp (F)

Use the colder planning temperature, not the seasonal average.

Envelope quality

Values represent BTU per sq ft at a 70 F indoor-to-outdoor delta before other multipliers.

Air leakage and exposure

This multiplier lets the same square footage behave more like a calm zone or an exposed zone.

Heating hours per day

This turns hourly burn rate into daily gallon demand.

Custom heating hours

Enter any realistic heating window from 1 to 24 hours.

Recovery buffer

Adds margin for recovery after setbacks and colder-than-planned swings.

Tank or cylinder size

Larger tanks generally maintain vapor delivery better during long cold burns.

Starting fill level

Choose the percentage when the heating event starts, not the rated maximum fill.

Reserve to keep untouched

This reserve stays below the usable gallon count shown in the runtime outputs.

Scenario note

This note appears in the result summary and helps tie the numbers back to the use case.

Propane Heating Summary

Your heating profile summary will appear here after calculation.

Ready for calculation

Estimated Heat Load0 BTU/h0.0 kW delivered heat

Propane Burn Rate0.00 gal/h0.00 L/h at appliance input

Conditioned Area0 sq ft0.0 sq m and 0 cu ft heated volume

Runtime Above Reserve0.0 days0.0 hours before reserve

Temperature delta0 F

Hourly appliance input0 BTU/h

Daily propane draw0.00 gal/day

Daily delivered heat0 kWh/day

Available gallons0.0 gal

Reserve threshold0.0 gal

Cylinder equivalent0.00 x 20-lb/day

Scenario notePrimary evening heat for one conditioned room.

⛽Propane Heating Constants

Fuel energy1 gallon of propane contains 91,500 BTU before appliance losses are applied.

20-lb cylinderA common grill cylinder holds about 4.7 gallons when full.

Load scalingEnvelope BTU per sq ft values are normalized to a 70 F design delta.

Reserve logicRuntime is calculated only on gallons above the selected reserve floor.

📊Appliance Profile Grid

95%Condensing furnaceBest for tight whole-home ducted systems with long winter runtimes.

82%Standard furnaceTypical for older induced-draft furnaces that still heat larger homes.

80%Wall furnaceUseful for cabin rooms and simple zone heating without duct losses.

78%Direct-vent stoveCommon living-space appliance with visible flame and moderate efficiency.

83%Unit heaterFast recovery for workshops and garage bays that cool off between uses.

87%Hydronic boilerSteady baseboard or radiant output where water loops store and spread heat.

99%Vent-free heaterHigh delivered heat for emergency zones where local code and ventilation allow it.

94%Combi boilerGood fit for low-temperature radiant loops and high-efficiency zone plans.

📋Reference Tables

Envelope Load Benchmarks

Envelope	Base load	Use case
Very tight	14 BTU/sq ft	Newer shell, balanced air sealing, lower winter infiltration.
Tight updated	18 BTU/sq ft	Updated insulation and windows, but still a conventional house.
Average	24 BTU/sq ft	Typical insulated shell with ordinary exterior wall exposure.
Older mixed	31 BTU/sq ft	Partial upgrades, mixed windows, or irregular air sealing.
Drafty	38 BTU/sq ft	High-loss zones, detached outbuildings, or loosely sealed rooms.

These values assume a 70 F indoor-to-outdoor delta before ceiling height, exposure, and buffer are applied.

Appliance Efficiency Comparison

Appliance	AFUE	Best fit
Condensing furnace	95%	Whole-home ducted heat where longer winter runtimes reward higher AFUE.
Standard furnace	82%	Existing homes with legacy duct systems and simpler venting.
Direct-vent stove	78%	Living rooms and additions that want targeted space heating.
Hydronic boiler	87%	Radiant slabs, baseboard loops, and slower steady-state zone loads.
Vent-free heater	99%	Short-duration emergency zones where local rules permit use.

Lower efficiency does not change the required room load. It increases the propane input needed to satisfy that load.

Tank Runtime Snapshot

Container	Usable at 80/20	Hours at 40k in
20-lb cylinder	2.8 gal	6.4 hr
100-lb cylinder	14.2 gal	32.5 hr
120-gal tank	34.2 gal	78.2 hr
250-gal tank	120.0 gal	274.5 hr
500-gal tank	240.0 gal	549.0 hr

Hours are based on 40,000 BTU per hour of appliance input, not delivered room heat.

Common Heating Scenarios

Project	Area	Load	Daily draw
Bedroom zone	168 sq ft	7-12k BTU/h	0.8-1.6 gal
Living room	320 sq ft	16-24k BTU/h	1.8-3.1 gal
Garage bay	480 sq ft	24-40k BTU/h	2.6-5.2 gal
Small house	1200 sq ft	36-58k BTU/h	4.7-8.5 gal
Whole home	2000 sq ft	60-90k BTU/h	7.9-13.1 gal

Ranges reflect different shell quality, exposure, and runtime windows rather than fuel pricing or installation choices.

💡Planning Notes

Use reserve as a hard floor

Cold-weather planning gets more realistic when you subtract the gallons you refuse to burn below. That keeps refill timing, emergency margin, and expected autonomy aligned with how most propane users actually manage tanks.

Check the load before you judge the tank

A tank that feels small on a drafty garage can look generous on a tight interior room. When you update area, ceiling height, or design temperature, burn rate changes faster than the container size itself.

To effectively manage propane usage, one must understand the relationship between the space that is to be heated and the propane fuel that such a space consumes. The propane that a given space consumes is dependent upon numerous factor, including the size of the space to be heated, the insulation of that space, and the difference in temperature between the indoors and outdoors. The size and condition of the space to be heated will impact the amount of propane that is require to heat that space.

Smaller space with high levels of insulation will require less propane to heat compared to larger spaces with low levels of insulation. Factors that contribute to the size of the space that must be heated include the size of the room and any high ceilings within that room. Propane appliances that is utilized to heat spaces will lose heat to the building envelope of the structure in which those appliances are located, especially if the structure isnt well-insulate.

How to Calculate Propane Use for Heating

The loss of heat from the building envelope causes those propane appliances to burn more propane in an effort to compensate for the loss of heat from the structure. The temperature difference within the space to be heated in comparison to the temperature outside of those structures is another critical factor in determining the consumption of propane by those appliances. The design temperature of the structure is the lowest temperature that will be experienced within the area in which the structure is located during the winter months.

The difference between the desired indoor temperature and the outdoor design temperature is referred to as the temperature difference, which impacts the load intensity that is placed upon the propane appliances. The higher the difference between the indoor and outdoor temperatures, the more higher the load intensity upon the appliances. Furthermore, different propane appliances will have different rates of efficiency in converting propane to heat; appliances with high levels of efficiency will release more heat from propane fuel relative to appliances with low levels of efficiency in performing such a task.

The size of the propane tank in which the propane fuel is stored will have an impact upon the length of time that the appliances can be used to heat the space. Because it is impossible to burn all of the propane that is contained within the tank, a propane reserve must be maintained within that tank. The amount of propane that is manufactured within the tank decrease as the propane appliances burn the propane for heating the space.

Furthermore, the size of the propane tank impacts the ability of that tank to function effective in cold weather climates. Small propane tanks have low levels of vapor pressure in their tanks relative to larger propane tanks. Low levels of vapor pressure in the tank indicate that the amount of propane that can be released from the tank to the appliance is less than in propane tanks with higher vapor pressure.

Thus, large propane tanks will have higher reliability in cold climates when using propane heating appliances. Calculations can be made of the number of days of propane that is available for those appliances based off the size of the propane tanks. The heat load in BTUs per hour that the appliances must release can be calculated, as can the burn rate in gallons per hour of propane.

With the heat load and burn rate of the appliances known, it is possible to calculate how many days the propane will last before the propane reserve is reached. Additionally, it is important to consider the runtime of those propane appliances; those appliances that are continuously running will consume more propane than those that are running for shorter period of time, such as for twelve hours as opposed to twenty-four hours per day. By considering all of the factors related to the system of heating with propane appliances, each of these factors can be addressed to reduce the consumption of propane fuel.

For instance, each structure can be better insulated to reduce the loss of heat to the environment, or the appliances can be managed with thermostats to reduce their runtime. Additionally, the location of propane tanks can be considered, as well; different locations may allow for different amount of propane to be delivered to the tanks. By planning for propane usage by calculating the square footage of the spaces to be heated, the size of the temperature difference between indoors and outdoors, and by calculating the amount of propane that should of been maintained in the tanks as a reserve, it is possible to avoid depletion of the propane tanks during the winter season.