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Comparing a propane heater to central heating on cost alone means comparing two different things: a portable unit heating one room, against a system heating an entire structure. Here’s how to make that comparison fairly, using your own local rates.
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Why This Comparison Needs Your Own Numbers
Electricity rates, natural gas rates and propane prices all vary by region, provider and season. A number published today can be outdated within months. Rather than quoting a rate that will go stale, this guide shows the formula so you can plug in your own local prices for an accurate comparison.
Propane Heater Cost Per Hour
Propane holds roughly 91,500 BTU per gallon, or about 21,600 BTU per pound. Divide your local price per gallon by 4.24 to get a price per pound, then divide your heater’s BTU rating by 21,600 to get pounds burned per hour. Multiply the two for your cost per hour. Our running cost calculator guide walks through this with a worked example.
Central Heating Cost Per Hour (Electric or Gas Furnace)
An electric furnace’s cost per hour depends on its wattage and your electricity rate per kilowatt-hour, printed on your utility bill. A gas furnace’s cost depends on its BTU input rating and your natural gas rate, typically billed per therm or per hundred cubic feet. Both numbers are specific to your home and provider — check your own utility bill or your furnace’s rated output for an accurate figure, rather than assuming a number found online applies to your situation.
Why the Comparison Isn’t Really Apples to Apples
Central heating warms an entire structure through ducting or radiators, while a portable propane heater warms one room or one space directly. Comparing their cost per hour only makes sense when you’re heating a similar area with both — for example, a detached garage that could plausibly get either a propane heater or a mini-split system, versus running the whole-house furnace just to warm one detached space it wasn’t designed to reach in the first place.
When Propane Comes Out Ahead
Propane heaters tend to win on cost specifically when you’re heating a space central heating doesn’t already reach — a detached garage, a workshop, a three-season porch — since the alternative isn’t "central heating instead," it’s "extending central heating to a new space," which usually costs far more than a portable heater ever would. They also win when usage is occasional rather than constant, since there’s no ongoing cost when the heater isn’t running, unlike a furnace’s baseline standby draw.
When Central Heating Comes Out Ahead
For a space central heating already reaches and heats adequately, running a portable propane heater on top of that system rarely saves money. You’re paying for two heat sources instead of one, and central systems are generally more efficient per BTU delivered at whole-structure scale than a portable radiant or forced-air unit. If your central system already reaches and adequately heats the space in question, it’s very likely the cheaper option to keep using.
Efficiency Differences Beyond Price Per BTU
Cost per hour is not the whole picture. A central furnace loses some heat through ductwork, especially older or poorly sealed systems. A portable propane heater loses none of that, since it heats the room it’s sitting in directly. But a portable heater also has no thermostat cycling it off automatically once a room is warm, so it can run longer than strictly needed if you’re not paying attention. Neither system is efficient by default. Both depend on how well they’re actually managed day to day.
A Realistic Example: Heating a Detached Garage
Picture a detached garage with no ductwork running to it at all. Extending central heating there means new ducting, a mini-split system, or an electrician running a dedicated circuit — a real installation cost before you’ve spent a dollar on actual heat. A portable propane heater sized to the garage, by contrast, costs far less upfront and starts working the same day. This is the scenario where propane usually wins clearly, not because it’s cheaper per BTU, but because the fair comparison isn’t "propane vs. existing central heat." It’s "propane vs. installing a new heating system from scratch."
A Simple Way to Compare Your Own Numbers
Calculate propane cost per hour using the formula above and your own local propane price. Check your utility bill for your electric or gas rate, and your furnace’s rated output, to calculate its cost per hour for the same space. Compare the two directly. The lower number, for the specific space you’re actually trying to heat, is your answer — not a general rule that applies to every situation.
Factoring In Installation and Upfront Costs
Running cost per hour is only half the comparison for a space that doesn’t already have central heating installed. Extending ductwork, adding a mini-split, or running a new electrical circuit to a detached structure carries a real installation cost, often well beyond what a portable propane heater costs outright. For a space you use occasionally, that upfront cost may never pay for itself compared to simply buying a propane heater for the handful of times a year you actually need heat there. For a space used daily through a long season, the math can tip the other way, since installed systems are typically more efficient per hour over years of regular use.
Seasonal Use vs. Year-Round Use
If you only need heat in a given space for a few weeks each winter, a portable propane heater’s lower upfront cost usually wins over installing any permanent system, regardless of the per-hour cost difference. If you’re heating that same space daily for months at a stretch, the ongoing efficiency of a properly sized permanent system starts to close the gap, and eventually surpass it, compared to running a portable unit for the same total hours. Match the type of heat source to how often you actually expect to use the space, not just to whichever option looks cheaper in an isolated per-hour calculation.