Propane or electric? Answer wrong and you either haul a tank you cannot refill in February or watch your battery bank die trying to run a resistance heater. Every tiny house has to pick its fuel, and the choice ripples into tank size, electrical service, solar array, and monthly cost.
BTU per gallon, BTU per kilowatt-hour, and your actual appliances: this guide runs the full comparison in plain numbers. You will learn the efficiency factors that change the answer, how to size a propane tank for real usage, and how to compare monthly costs honestly. Pick your fuel with a calculator, not a hunch.
The Fuel Decision Shapes Everything
Every tiny house answers the same question: propane, electric, or both? The answer determines the tank size, the electrical service, the solar array, and the monthly costs. This guide does the fuel math — energy content, demand calculation, and tank sizing — so the decision is engineering, not guesswork.
1. Energy Content: The Common Currency
Compare fuels in BTU: propane: 91,500 BTU per gallon. Electricity: 3,412 BTU per kWh. One gallon of propane ≈ 26.8 kWh of electricity (before efficiency). Efficiency matters: a propane furnace at 90% AFUE delivers ~82,000 BTU/gallon; resistance electric is 100% efficient at the point of use (but the power plant wasn’t); a mini-split heat pump at COP 3.0 delivers ~10,200 BTU/kWh — 3× resistance heat. Cost comparison: at $3/gallon propane vs $0.15/kWh electricity: propane heat costs ~$36.60 per million BTU; resistance electric ~$44/million BTU; heat pump ~$14.70/million BTU. The heat pump wins on operating cost wherever electricity is available.
2. The Demand Audit: What Burns What
Typical tiny house loads: space heating: 5,000–15,000 BTU/hr in winter (the big one — 120,000–360,000 BTU/day in cold climates). Water heating: 30,000–40,000 BTU/day for two people (showers + dishes). Cooking: 10,000–20,000 BTU/day. Clothes drying: 20,000 BTU/load (if gas). Total propane demand (heat + hot water + cooking): 0.5–2 gallons/day in heating season, 0.2–0.5 gallons/day in summer. Electric equivalents: heating via mini-split 2–5 kWh/day (mild) to 10–20 kWh/day (cold); water heating 3–5 kWh/day; cooking 1–2 kWh/day.
3. Propane System: Tank Sizing
Tank options: 20-lb BBQ cylinders (4.6 gallons — the portable option; swap at any gas station), 30/40-lb RV cylinders (7–9.5 gallons — the tiny house standard pair), 100-lb cylinders (23.6 gallons — fewer refills), 120-gallon ASME tank (permanent — the homestead option). Sizing math: winter demand 1.5 gal/day × 30 days = 45 gallons/month → two 40-lb cylinders (19 gallons) last ~12 days; a 100-lb cylinder (23.6 gal) ~16 days; a 120-gallon tank (96 usable gallons — filled to 80%) ~64 days. The rule: size for the refill interval you tolerate (monthly refills = 100-lb+; seasonal = 120-gallon ASME). Placement: outside, ventilated compartment or open rack (propane sinks — never in a sealed basement; 10+ feet from ignition sources per code).
4. Propane Safety: The Non-Negotiables
Detector: propane detector mounted LOW (propane sinks — $30, hardwired with battery backup — the cheapest life insurance). Lines: black iron or CSST (corrugated stainless — flexible, DIY-friendly with proper fittings), pressure-tested at install (the pro soap-bubbles every joint — do the same). Regulator: two-stage (tank pressure to 11″ water column — the standard; protect it from weather). Shutoff: accessible main shutoff + per-appliance shutoffs (label them). Never: store spare cylinders inside (outside only), use unvented heaters as primary heat (the moisture and CO risk), or ignore the rotten-egg smell (leave, shut off gas outside if safe, call for help).
5. Electric System: Service and Load Sizing
All-electric tiny house loads: mini-split heating 1,000–2,000W running, water heater 1,500–4,500W, cooktop 1,800–3,600W, dryer 2,500–5,000W, plus baseline 500W. Peak concurrent: easily 8,000–12,000W — this is why all-electric houses need 50-amp service (12,000W capacity). Off-grid all-electric: the hard path — 15–25 kWh/day needs a 4–6 kW solar array and 30–45 kWh of batteries ($20,000–35,000 for the power system). The realistic off-grid electric: mini-split + efficient appliances on solar, with propane for water heating and cooking (the hybrid — see below).
6. The Hybrid: The Tiny House Standard
Most successful off-grid tiny houses run both: propane for: water heating (on-demand — the big win), cooking (instant, powerful, no electrical load), and backup space heat (a small propane furnace or wall heater for the coldest nights). Electric (solar) for: mini-split (primary heating/cooling — the efficiency king), lights, electronics, fridge, and small appliances. Why the hybrid wins: propane handles the energy-dense thermal loads (heating water and cooking need enormous energy — propane stores it densely), electricity handles everything else (solar is perfect for moderate loads). Typical setup: two 40-lb propane cylinders + 2–3 kW solar + 10–15 kWh batteries + 9k BTU mini-split. Monthly propane: $30–80. The hybrid is the engineering optimum for off-grid tiny living.
7. Costs: 10-Year Comparison
All-propane (heat + hot water + cooking): ~400–600 gallons/year × $3 = $1,200–1,800/year. All-electric (grid): ~6,000–9,000 kWh/year × $0.15 = $900–1,350/year (heat pump) or $2,000–3,000 (resistance). Hybrid off-grid: ~150–250 gallons propane ($450–750) + solar system amortized (~$800–1,200/year over 20 years) = $1,250–1,950/year with zero utility dependence. The verdict: grid-tied heat pump electric is cheapest where the grid exists; off-grid, the hybrid minimizes both cost and complexity. Pure resistance electric off-grid is the most expensive option by far.
Final Considerations
Do the demand audit, size the propane for your refill tolerance, size the electric for the peak concurrent load, default to the hybrid (propane for thermal loads, solar electric for the rest), and never skip the propane detector. Fuel choice is the invisible architecture of the tiny house — get the math right and comfort follows for decades.