Propane usage & tank calculator

Propane is a quiet workhorse in many off-grid setups: it cooks, heats water, keeps a fridge cold, and backs up the heat, all without touching the battery bank. This calculator adds up what your particular mix of appliances burns, splits it into a summer picture and a winter picture, and tells you what size tank keeps the delivery truck from becoming a monthly visitor.

What each appliance really burns

The monthly figures behind the checkboxes are honest household averages: a cooking range runs around 3 to 5 gallons a month, a tank-style water heater 15 to 20, an on-demand unit noticeably less because it only burns while water flows, a propane fridge around 5 to 7, and a dryer a few gallons depending on loads. Your numbers will drift with habits, a family of five showers more than a couple, but the totals land close enough to size a tank and a budget.

Heat is the number that changes everything, which is why it gets its own inputs. A 30,000 BTU direct-vent heater running six hours a day burns roughly 60 gallons a month by itself. If propane is your primary winter heat in a cold climate, it will dwarf every appliance combined, and it is worth running the heat loss calculator to see what insulation would do to that line item, and the firewood calculator to price the wood-heat alternative.

Picking the tank: 120, 250, or 500 gallons

Tanks fill to 80 percent so the vapor space can expand, so a "500 gallon" tank holds about 400 usable gallons. The right size is the one where a winter fill lasts comfortably past two months and you need somewhere between one and four deliveries a year. Small 120 gallon tanks suit cooking-and-hot-water households; once propane carries real heating load, a 250 or 500 earns its pad fast.

Two practical notes that matter more than the math. First, owned versus rented: a rented tank locks you into that supplier's per-gallon price, which is often 50 cents to a dollar above market, while an owned tank lets you shop every fill. It usually pays for itself in a few years. Second, remote properties should size up a step, deliveries carry minimums, winter roads cancel trucks, and the tank that never runs dry in February is the one a size bigger than the spreadsheet said.

Where propane fits in the bigger energy picture

The rule that keeps off-grid systems affordable: electricity from batteries for light loads, and combustion for heat loads. Making heat from stored sunshine is brutally expensive per BTU; making it from propane or wood is cheap. That is why the classic setup pairs a modest solar system with propane for cooking, hot water, and backup heat, and why an all-electric off-grid build needs a solar array several times larger. The generator calculator covers the other big propane consumer, and the Heating & Cooking archive digs into the appliance choices themselves.

Getting a useful answer out of this

Propane usage & tank size returns summer use, winter use, tank that fits, and refills per year. Every one of those is a planning figure rather than a specification: it tells you the size of the problem and roughly what it will take to solve, which is what you need before you can shortlist equipment or ask a supplier a sensible question.

The single most useful habit with any calculator on this site is to run it more than once. Change one input at a time and watch which output moves. That tells you where your design is sensitive, and design sensitivity is far more valuable than a single answer, because it identifies the assumption worth spending real effort to pin down. If a modest change in one input swings the result substantially, that input deserves a measurement rather than an estimate.

It is also worth running the pessimistic version. Off-grid systems are sized by their worst case rather than their average, and a design that only works on the numbers you hoped for is a design that works for part of the year. Put in the colder temperature, the longer run, the larger household, the dimmer month, and see whether the answer is still one you can live with.

What a calculator cannot know

Any tool like this works from the inputs you give it and from published averages for everything else. It does not know your particular site, the way your household actually behaves, the corner your building was cut in, or the ten-year-old equipment already installed that does not match its datasheet. Treat the output as a well-informed starting bracket, not as a specification to order against.

Three things in particular sit outside what any of these tools can see. The first is local rules, which decide what you may build regardless of what the arithmetic says: the laws pages cover those by state, county, and town. The second is the condition and quality of what you install, which is why two identical designs perform differently. The third is how the system is wired and protected, which decides whether it is safe rather than whether it is adequate, and which is the subject of lesson six.

Where a number here comes from a constant or a rule of thumb, the method notes above say so and give the source. That is deliberate: a result you cannot check is a result you should not act on, and the arithmetic here is simple enough to verify by hand on paper if you want to.

Where to take the answer next

A single figure rarely settles anything on its own, because off-grid systems constrain each other. The load list decides the array, the array decides the controller, the battery decides what the inverter can deliver, and the climate at your site decides all of it. The system planner takes one set of inputs and produces a whole coherent plan rather than an isolated number, which is usually the better next step once you have a figure you trust.

For location-specific inputs, the site report gives any address its real 30-year sun, climate, elevation, and distance figures, including the worst-month sun hours that size an off-grid system properly. For the equipment that the result points at, the spec tables list what manufacturers publish, normalised so that units of different sizes can be compared, and each product page works its own numbers through. For what things cost this month, the price index.

And for the reasoning rather than the arithmetic, the free course runs through the decisions in the order they actually arrive, from deciding whether the life suits you through to the first year on the land. Most of the mistakes that calculators cannot prevent are ordering mistakes, made before anyone opened a calculator at all.