Heating and cooling are the loads that break most off-grid plans. A laptop, some lights, and a 12V fridge add up to a couple thousand watt-hours a day, the kind of number a modest solar array swallows without complaint. Then someone tries to plug in a 1,500-watt space heater for the winter, or a window air conditioner for July, and the entire system falls over. This guide gives you the honest physics first, then walks through every realistic way to stay warm and cool off-grid, with the real numbers for each: BTU output, fuel and electricity consumption, sizing tables, install and code notes, and exactly what battery bank the electric options demand.
The short version, before you read another word: heat with fire, cool with a heat pump or evaporation, and insulate before you do either. Electricity is a wonderful way to run a fridge, charge a phone, and pump water. It is a terrible way to make raw heat. Understanding why that is true, and where the exceptions live, is the difference between a comfortable cabin and a dead battery bank at 3 a.m. in January.
The Honest Energy Math (Read This First)
Heat is measured in BTUs (British Thermal Units). One BTU is the energy needed to raise one pound of water by one degree Fahrenheit. A small cabin in a cold climate might need 20,000-40,000 BTU per hour on a freezing night. Now watch what happens when you try to supply that with electricity.
Resistance electric heat (every space heater, baseboard, and electric furnace) converts electricity to heat at a fixed exchange rate: 1 watt-hour of electricity equals 3.412 BTU of heat. That sounds efficient, and at the point of conversion it is 100% efficient. The problem is the scale. To make 30,000 BTU per hour with resistance heat you need 30,000 / 3.412 = about 8,792 watts, nearly 9 kW, running continuously. Over a 16-hour winter night that is roughly 140 kWh. No off-grid solar system on a normal budget can deliver that. You would need a 30-40 kW array and a 150+ kWh battery bank to run a single electric furnace overnight.
Fuel-burning heat changes the math entirely because the energy is already stored in the fuel; you are not asking your battery bank to manufacture it. A pound of dry firewood holds roughly 6,000-7,000 BTU. A gallon of propane holds about 91,500 BTU. A gallon of diesel or kerosene holds about 138,000 BTU. Your batteries only have to run a small fan or igniter, which sips watt-hours instead of gulping them.
BTU per Watt-Hour by Method
This is the table that should anchor every decision on the page. It shows how much usable heat you get per unit of electricity consumed. Fuel methods produce enormous heat for almost no electrical draw, which is exactly why they win for primary heat.
| Heating Method | Energy Source | Electric Draw | Usable BTU per Wh of Electricity | Off-Grid Verdict |
|---|---|---|---|---|
| Resistance electric (space heater, baseboard) | Electricity | Very high (1,000-1,500W) | 3.4 BTU/Wh | Avoid — ruinous load |
| Heat-pump mini-split (heating mode) | Electricity | Moderate (300-1,000W) | ~8.5-13.6 BTU/Wh (COP 2.5-4) | Viable with battery bank |
| Wood stove | Firewood | ~0W (none, or small fan) | Effectively unlimited per Wh | Best primary heat |
| Propane heater (vented) | Propane | Tiny (igniter/thermostat) | Effectively unlimited per Wh | Excellent |
| Diesel air heater | Diesel/kerosene | Low (6-18W running) | ~200-600 BTU/Wh of electricity | Excellent for vans/small cabins |
Read the fourth column carefully. Resistance heat gives you 3.4 BTU for every watt-hour, and there is no way around that ceiling — it is physics. A heat-pump mini-split cheats the rule by moving heat instead of making it, delivering 2.5 to 4 times more heat energy than the electricity it consumes (its Coefficient of Performance, or COP). Fuel methods barely register on the electric meter at all because the energy is in the wood, propane, or diesel, not your battery. The practical takeaway: off-grid, make heat from fuel and use electricity only for a heat pump or fans.
Insulate First: The R-Value Table
Before you spend a dollar on a heat source or a watt on cooling, spend it on the envelope. Every BTU you do not lose is a BTU you never have to produce. R-value measures resistance to heat flow; higher is better. Air sealing matters just as much as R-value, because a leaky building loses heat through convection no matter how thick the insulation. The cheapest, most effective off-grid HVAC upgrade is almost always insulation and a tube of caulk, not a bigger stove.
| Building Component | Minimum (Mild Climate) | Recommended (Cold Climate) | Off-Grid Target |
|---|---|---|---|
| Walls | R-13 | R-20 to R-21 | R-21+ (2x6 framing or rigid foam) |
| Ceiling / Roof | R-30 | R-49 | R-49 to R-60 |
| Floor (over crawlspace) | R-13 | R-25 to R-30 | R-30 |
| Windows (U-factor) | U-0.35 (double pane) | U-0.27 (low-E double) | U-0.20 or lower (triple pane) |
| Van / tiny build walls | R-7 (1.5" foam) | R-13 (3" foam board) | R-13+ with no thermal bridges |
The payoff is dramatic. Raising walls from R-13 to R-21 and the ceiling from R-30 to R-49, then sealing the obvious air leaks (rim joists, plumbing penetrations, door sweeps, window trim), routinely cuts heating and cooling load by 30-50%. That means a smaller wood stove, less propane, fewer mini-split kWh, and a smaller battery bank. Passive design choices stack on top: orient the building so south-facing windows collect winter sun, add roof overhangs that block the high summer sun but let in low winter sun, and use thermal mass (a tile floor, a masonry stove surround, water barrels) to soak up daytime heat and release it at night. None of this consumes a single watt-hour.
Off-Grid Heating Options
With the envelope tightened, you can size a heat source to a much smaller load. Here are the four realistic ways to heat off-grid, ranked roughly from least to most electrical dependence: wood, propane, diesel, and the heat-pump mini-split.
Wood Stoves (Sizing, Install & Code)
A wood stove is the default primary heat for serious off-grid homes, and for good reason. It needs zero electricity, the fuel can be free if you have trees, it keeps working in a multi-day storm when nothing else does, and a cast-iron or steel stove will outlive you. The trade-offs are real: hauling and splitting wood is labor, you must tend the fire, ash and creosote require maintenance, and a poorly installed stove is a genuine fire and carbon-monoxide hazard.
Sizing by square footage. The most common mistake is buying too big a stove. An oversized stove forces you to run it choked down with the air closed, which smolders, wastes wood, and cakes your chimney with creosote. Size to your insulated, sealed square footage using roughly 25-40 BTU per square foot per hour for cold climates and average insulation.
| Stove Class | BTU/hr Output | Heats (Avg Insulation) | Heats (Well Insulated) | Typical Firebox |
|---|---|---|---|---|
| Small | 25,000-40,000 | 500-900 sq ft | up to 1,200 sq ft | 0.8-1.5 cu ft |
| Medium | 40,000-65,000 | 900-1,600 sq ft | up to 2,000 sq ft | 1.5-2.5 cu ft |
| Large | 65,000-90,000+ | 1,600-2,800 sq ft | up to 3,500 sq ft | 2.5-4.0 cu ft |
Install basics. A safe wood stove install comes down to clearances, the hearth, and the chimney. Maintain the manufacturer's specified clearance to combustibles (typically 16-36 inches to unprotected walls; listed heat shields can reduce this). Set the stove on a non-combustible hearth pad that extends 16-18 inches in front of the loading door and 8-12 inches to the sides. Run a proper insulated Class A chimney that terminates at least 3 feet above the roof penetration and 2 feet above anything within 10 feet (the "3-2-10 rule"). Keep the flue diameter matched to the stove's collar. A straight, tall flue drafts better and creosotes less than one with multiple elbows.
Code notes. Wood stoves are governed by NFPA 211 and your local building code, and the unit should carry a UL or equivalent listing. Many jurisdictions require an EPA-certified stove (2020 NSPS standard) for new installs, which also burns far cleaner and more efficiently. A permit and an inspection are common requirements; insurance carriers frequently demand a professional install or a WETT/NFI inspection. Always run a working carbon-monoxide alarm in any space with a combustion appliance.
Propane Heaters (Direct-Vent vs Vent-Free)
Propane is the most flexible off-grid heat after wood. A gallon of propane holds about 91,500 BTU, a 20 lb cylinder holds roughly 4.6 gallons (about 430,000 BTU usable), and a 100 lb cylinder or a buried tank holds far more. The electrical draw is essentially nothing — a piezo igniter or a millivolt thermostat that runs off the pilot's own heat, or a tiny 12V valve. The critical decision is how the heater handles its combustion air and exhaust.
Direct-vent / sealed combustion. These heaters pull combustion air from outside through one pipe and exhaust outside through another, so the burn is completely sealed off from your indoor air. They add no moisture or CO to the room, which makes them the right choice for off-grid bedrooms and tight, well-insulated builds. Wall-mounted direct-vent units (such as the Williams or Empire lines) are a popular permanent cabin solution. The downside is they cost more and require a through-wall vent install.
Vent-free (ventless). These dump 99.9% of their heat — and all their combustion byproducts, including water vapor and carbon monoxide — directly into the room. They are cheaper, need no venting, and are convenient, but they are also the riskier option. They consume room oxygen, add humidity that can cause condensation and mold in a tight cabin, and require an oxygen-depletion sensor (ODS) plus cracked-window makeup air. Never run a vent-free heater in a bedroom or while sleeping, and never in a sealed space. Many jurisdictions restrict or ban them in bedrooms and bathrooms.
| Propane Heater Output | Burn Rate (full) | 20 lb Tank Runtime (full) | 24 hr Use (50% duty cycle) | Best Use |
|---|---|---|---|---|
| 9,000 BTU/hr | ~0.10 gal/hr | ~46 hrs | ~1.2 gal/day | Tiny home, small cabin |
| 18,000 BTU/hr | ~0.20 gal/hr | ~23 hrs | ~2.4 gal/day | 1-2 room cabin |
| 30,000 BTU/hr | ~0.33 gal/hr | ~14 hrs | ~4.0 gal/day | Whole small cabin |
One often-overlooked detail: in very cold weather a 20 lb cylinder can struggle to vaporize propane fast enough for a large heater, causing the flame to drop. For sustained cold-climate heating, use a larger cylinder or a manifolded pair so the liquid surface area can keep up with demand.
Diesel Air Heaters (The Van Favorite)
The diesel air heater (the Webasto/Espar design, plus the inexpensive Chinese clones) has quietly become the standard heat source for van life and small off-grid builds, and the reason is the numbers. It produces a lot of dry, vented heat for almost no electricity and a tiny amount of fuel, and it exhausts all combustion gases outside through a sealed circuit.
Actual electrical draw. On startup the glow plug pulls 8-12 amps at 12V for about 2-4 minutes to light the fuel. Once running, the unit settles to roughly 0.5-1.5 amps (6-18 watts) to power the combustion air fan and circulation fan. Over a full night that is only about 100-300 watt-hours of electricity — a load any 100Ah house battery shrugs off. This is why diesel heaters are the "van favorite": they keep you warm overnight while barely touching the battery your panels recharge by lunch.
| Diesel Heater Size | Heat Output | Fuel Burn (low-med) | Running Electric Draw | 24 hr Fuel Use |
|---|---|---|---|---|
| 2 kW | ~6,800 BTU/hr | 0.02-0.04 gal/hr | 6-12 W | ~0.5-0.9 gal |
| 5 kW | ~17,000 BTU/hr | 0.03-0.06 gal/hr | 8-18 W | ~0.7-1.4 gal |
| 8 kW | ~27,000 BTU/hr | 0.05-0.10 gal/hr | 10-22 W | ~1.2-2.4 gal |
For a van or a small cabin, a 2 kW unit is usually plenty; people often buy the 5 kW "because bigger" and then run it on the lowest setting, which can soot up the burner over time. Mount the fuel pump on a soft bracket to quiet its tick, route the exhaust well away from sleeping windows and any fresh-air intake, and run a CO alarm — the burn is sealed, but a cracked exhaust or a poorly routed muffler is a real hazard. For the full van build context, see our van life solar system guide.
Mini-Splits: The One Electric Exception
Here is where electricity finally earns its place in heating. A mini-split is an inverter-driven heat pump that moves heat rather than generating it, so it can deliver 2.5-4 BTU of heat for every BTU of electricity it consumes — a COP of 2.5-4. That is 3-4 times better than a resistance heater, and it makes electric heat finally defensible off-grid, provided you have the battery bank to feed it. The same unit reverses in summer to provide efficient cooling, so a single appliance covers both seasons.
What the specs mean. SEER and SEER2 rate cooling-season efficiency (higher is better; modern off-grid-friendly units are SEER2 18-28). HSPF rates heating-season efficiency. For off-grid purposes the number that matters most is the actual daily kWh the unit draws in your climate, because that is what your panels must replace and your battery must store overnight. The table below gives realistic daily consumption for a 9,000 BTU (3/4-ton) high-efficiency inverter mini-split; a 12,000 BTU unit roughly scales these figures up by 30-50%.
| Climate / Season | Running Draw | Daily kWh (9k BTU) | Daily kWh (12k BTU) | Usable Battery Needed (1-2 day buffer) |
|---|---|---|---|---|
| Mild cooling (75-85°F) | 300-500 W | 2.5-4 kWh | 3.5-6 kWh | 5-8 kWh |
| Hot cooling (95-105°F) | 500-800 W | 6-9 kWh | 8-12 kWh | 10-18 kWh |
| Mild heating (35-45°F) | 350-600 W | 3-5 kWh | 4-7 kWh | 6-10 kWh |
| Cold heating (10-25°F) | 700-1,200 W | 7-11 kWh | 9-14 kWh | 12-20 kWh |
What battery bank it requires. Take the daily kWh, figure how much of it runs overnight when there is no sun, and add a cloudy-day buffer. A 9,000 BTU unit sipping 4 kWh/day in a mild climate uses roughly 1.5-2 kWh overnight; for one to two days of autonomy you want about 5-8 kWh of usable storage, which is a 48V LiFePO4 bank of roughly 100-160Ah. Push into hot-summer or cold-winter operation and you are looking at 10-20 kWh of storage and a 2-4 kW array to recharge it. Cold-climate caveat: heat-pump COP falls as it gets colder, and below about 5-15°F (depending on the unit) a standard mini-split loses capacity and may switch to inefficient backup resistance heat — exactly when your solar production is also at its winter low. For deep-cold climates, keep a wood stove or propane heater as primary and treat the mini-split as shoulder-season comfort. Size the storage with the DIY solar battery bank guide and confirm amp-hours with the calculator below.
Off-Grid Cooling Options
Cooling is the summer mirror of the heating problem. You cannot "burn fuel" to make cold, so every real cooling option is either electric (a compressor) or relies on water evaporation. The good news is that the same heat-pump mini-split that warms you in winter cools you efficiently in summer, and in dry climates evaporative cooling can do the job for a fraction of the power.
Evaporative vs Air Conditioning
Evaporative ("swamp") coolers pull air through a wet pad; as the water evaporates it absorbs heat and drops the air temperature 15-25°F. They are astonishingly efficient — a unit cooling a room might draw only 50-150 watts versus 400-800 watts for a comparable air conditioner — because they are basically a fan plus a water pump. The catch is humidity. Evaporative cooling only works in dry air (relative humidity below roughly 40-50%); in a humid climate it does almost nothing except make the room muggier. They also add moisture and require a water supply, which is a consideration if your off-grid water is precious.
Air conditioning (window units, portable units, RV rooftop units, and mini-splits) uses a refrigerant compressor to actively pump heat outdoors. It works in any humidity and also dehumidifies, which is the only real option in the muggy Southeast or anywhere near the coast. The cost is power: even a small unit is a heavy off-grid load, and a compressor's startup surge demands a robust inverter. Inverter-driven mini-splits and DC-powered units are far more off-grid-friendly than a cheap on/off window box, because they modulate their draw instead of slamming on at full power every cycle.
| Cooling Method | Running Watts | Daily kWh (8 hr) | Works in Humidity? | Off-Grid Notes |
|---|---|---|---|---|
| Evaporative cooler | 50-150 W | 0.4-1.2 kWh | No (dry climates only) | Cheapest to run; needs water |
| 5,000-8,000 BTU window AC | 400-700 W | 3-6 kWh | Yes | High surge; needs robust inverter |
| Portable AC | 800-1,400 W | 5-10 kWh | Yes | Least efficient; avoid off-grid |
| 9,000 BTU inverter mini-split | 300-700 W | 2.5-6 kWh | Yes | Most efficient compressor cooling |
| 12V/DC rooftop or marine AC | 300-600 W (DC) | 2.5-5 kWh | Yes | No inverter loss; good for vans/boats |
Estimating Your Cooling Load
Sizing cooling starts with a rough BTU load, then converts to power. A common starting point is about 20 BTU per square foot of conditioned space, adjusted up for sun exposure, poor insulation, high ceilings, and the number of occupants and heat-producing appliances. A well-shaded, well-insulated 400 sq ft cabin might only need 6,000-8,000 BTU of cooling; a sun-baked, leaky 600 sq ft space could need 12,000-15,000 BTU.
To turn BTU into a daily energy number, divide the cooling BTU/hr by the unit's EER (BTU per watt; a decent inverter unit is EER 10-14) to get running watts, then multiply by the hours per day you will actually run it. Example: an 8,000 BTU mini-split at EER 12 draws about 667 watts; running it 8 hours a day is roughly 5.3 kWh/day. That number drives everything downstream — array size and battery size. Insulation and shade are once again your best friends here: every BTU of cooling load you eliminate with a roof overhang or a shade tree is a watt-hour you never have to store. Drop your numbers into the Load Calculator to see the array and battery your cooling plan implies, and read the full storage walkthrough in our battery bank guide.
Can I Run a Mini-Split Off-Grid?
Yes — a mini-split is the one electric heating and cooling option that genuinely works off-grid, as long as you build the battery bank to feed it. A 9,000 BTU inverter mini-split draws roughly 300-700 watts while running and consumes about 2.5-6 kWh per day in moderate climates, rising to 8-12 kWh per day in extreme heat or deep cold. To run that overnight and through a cloudy stretch you want a 48V LiFePO4 battery bank of about 5-10 kWh usable (more in harsh climates), paired with roughly 1,500-3,000 watts of solar to recharge it during the day. A 12,000 BTU unit roughly doubles the storage and array. The reason it works where a space heater does not is the heat pump's COP of 2.5-4: it moves several units of heat per unit of electricity instead of converting one-for-one. Plan for the worst-case season, derate lead-acid batteries to 50% depth of discharge, and confirm your amp-hours with the Battery Bank Calculator before you buy anything.
Is It Worth Heating With Electricity Off-Grid?
For resistance electric heat, almost never; for a heat-pump mini-split, often yes. A 1,500-watt electric space heater consumes 36 kWh in 24 hours, which would demand a 7-10 kW array and a 30+ kWh battery bank just to warm one room overnight — tens of thousands of dollars of equipment to do a job a $400 propane heater or a wood stove does for a fraction of the cost. That is the honest math the page opened with: converting electricity straight to heat is the single most expensive way to stay warm off-grid. The mini-split is the exception precisely because it does not convert; it moves heat at a COP of 2.5-4, so it sips a third to a quarter of the power. For primary heat in a cold climate, lead with fuel: a wood stove or a vented propane heater is dramatically cheaper per BTU and keeps working when the panels are buried in snow. Use electric heat (the mini-split) for shoulder-season comfort, mild climates, and the convenience of one appliance that also cools in summer.
For the bigger picture of sizing a complete system around these loads, our off-grid cabin solar system guide and tiny home solar system guide walk through panels, controllers, and wiring end to end, and the off-grid refrigeration guide covers the other always-on load that competes with HVAC for your battery capacity.
Frequently Asked Questions
Can I run a mini-split off-grid?
Yes, a mini-split is the one electric heating and cooling option that is genuinely practical off-grid, but only with the right battery bank. A 9,000 BTU (3/4-ton) inverter mini-split draws roughly 300-700 watts while running and consumes about 3-6 kWh per day in moderate climates, rising to 8-12 kWh per day in extreme heat or cold. To run it overnight you need a 48V LiFePO4 battery bank of at least 5-10 kWh of usable capacity, plus 1,500-3,000 watts of solar to recharge during the day. A 12,000 BTU unit roughly doubles those numbers. Use the Battery Bank Calculator to size storage for your specific daily kWh.
Is it worth heating an off-grid cabin with electricity?
For resistance electric heat (space heaters, baseboards), almost never. A 1,500-watt electric heater consumes 36 kWh in 24 hours, which would require a 7-10 kW solar array and a 30+ kWh battery bank just to run one room overnight — tens of thousands of dollars in equipment. The honest math is that converting electricity to heat is the most expensive way to stay warm off-grid. The exceptions are heat-pump mini-splits, which deliver 2.5-4 units of heat per unit of electricity (a COP of 2.5-4), making them 3-4x more efficient than resistance heat. For primary heat, wood, propane, and diesel are dramatically cheaper per BTU.
What size wood stove do I need for my cabin?
As a rough rule, you need about 30-40 BTU per square foot per hour for an average-insulation home in a cold climate, or 20-30 BTU/sq ft in a well-insulated, milder one. A small stove rated around 25,000-40,000 BTU heats roughly 500-1,000 sq ft, a medium stove of 45,000-65,000 BTU heats 1,000-1,800 sq ft, and a large stove of 65,000+ BTU heats 1,800-3,000 sq ft. Oversizing is a common mistake: a stove that is too big forces you to run it choked down, which produces creosote and smoke. Size to your insulated, sealed square footage, not your dream square footage.
How much electricity does a diesel heater use?
Very little, which is why diesel air heaters are the favorite for vans and small cabins. A 2-5 kW Chinese diesel heater draws 8-12 amps at 12V for about 2-4 minutes during glow-plug startup, then settles to roughly 0.5-1.5 amps (6-18 watts) while running. Over a full night it uses only about 100-300 watt-hours of electricity, which any modest 100Ah battery handles easily. The fuel side is the real cost: it burns roughly 0.03-0.06 gallons of diesel per hour on low to medium, or about 0.7-1.4 gallons in 24 hours of continuous running.
Are vent-free propane heaters safe indoors?
Vent-free (ventless) propane heaters are legal in many areas and have an oxygen-depletion sensor that shuts the unit off if oxygen falls too low, but they release all combustion byproducts, including water vapor and carbon monoxide, directly into the room. They must never be used in a bedroom or a tightly sealed space, require a cracked window for makeup air, and demand a working battery CO detector. Direct-vent and sealed-combustion propane heaters are far safer for off-grid sleeping spaces because they draw combustion air from outside and exhaust outside, keeping the burn completely separated from your breathing air.
Can I run air conditioning off-grid?
Yes, but cooling load is heavy, so you need either an efficient inverter mini-split or to lower your expectations. A small 5,000-8,000 BTU window or portable AC draws 400-700 watts and consumes 4-8 kWh per day, requiring roughly 1,500-2,500 watts of solar and 5-8 kWh of usable battery. A DC-powered RV rooftop or 12V/48V mini-split is more efficient. In dry climates an evaporative (swamp) cooler does the same comfort job on a fraction of the power, often 50-150 watts. In humid climates evaporative cooling fails and a compressor-based system is the only real option.
What is the most efficient off-grid heating method?
Measured by cost per usable BTU, a well-run wood stove is usually the cheapest, especially if you cut your own wood, followed by propane and diesel. Measured by electrical efficiency, a heat-pump mini-split is the most efficient electric option at a COP of 2.5-4. But the single most effective "heating" upgrade is not a heat source at all, it is insulation and air sealing. Raising walls from R-13 to R-21 and sealing air leaks can cut heating load by 30-50%, which shrinks every downstream system. Always insulate first, then size the heat source to the reduced load.
How big a battery bank do I need for a mini-split?
Size the battery to cover overnight runtime plus a cloudy-day buffer. A 9,000 BTU mini-split consuming 4 kWh per day uses roughly 1.5-2 kWh overnight. For one to two days of autonomy you want about 5-10 kWh of usable storage, which is a 48V bank of roughly 100-200Ah of LiFePO4. A 12,000 BTU unit in a hot or cold climate consuming 8-12 kWh per day needs 10-20 kWh of usable storage. Always size to your real measured daily kWh, derate lead-acid to 50% depth of discharge, and use the Battery Bank Calculator to confirm amp-hours at your system voltage.