Emergency Shelter Heating Calculator

Why emergency heating planning matters

When the power goes out in winter, the first 24-48 hours determine whether you stay warm or face hypothermia risk. Most people massively underestimate how much fuel they need to heat even a small space — and overestimate how long their backup supply will last.

The polar vortex outages of February 2021 in Texas killed over 200 people, many from hypothermia in heated homes that lost power for days. Similar events happen yearly across the US Northeast, Midwest, and Mountain West. Having a heating plan and adequate fuel is a survival issue, not a convenience.

The heat loss formula

The fundamental equation:

BTU per hour = Room volume (ft³) × Temperature difference (°F) × Infiltration factor

Where:

• Room volume: floor area × ceiling height
• Temperature difference: indoor target − outdoor temperature
• Infiltration factor: accounts for insulation quality and air leakage

Worked example: 200 sq ft room with 8-ft ceiling, 60°F target, 20°F outside, average insulation:

• Volume: 1,600 ft³
• ΔT: 40°F
• Infiltration: 0.25
• BTU/hr: 1,600 × 40 × 0.25 = 16,000 BTU/hr

That’s a substantial heat output — equivalent to running a typical kerosene heater at full power continuously.

Insulation factors

The infiltration factor varies dramatically with building quality:

Fuel energy density (after efficiency)

Different fuels have different usable energy after combustion efficiency:

A propane tank (20 lb / 4.7 gallons) provides about 343,000 BTU of usable heat — enough to run a 16,000 BTU/hr heater for about 21 hours.

Realistic fuel storage estimates

For a 7-day power outage at 20°F outside heating a 200 sq ft room to 60°F:

• Total heat needed: 16,000 BTU/hr × 24 hr × 7 days = 2,688,000 BTU

Note these are continuous heating estimates. With sleep-time temperature reduction (50°F at night with blankets), you can cut fuel use 30-40%.

Practical fuel storage considerations

Propane (20 lb tanks):

• Most accessible (exchange programs at every gas station)
• Each tank: ~4.7 gallons = ~343,000 BTU
• Indoor use requires extreme caution (CO risk)
• Outdoor storage required
• Tank inspection required every 12 years

Kerosene:

• High energy density
• Long shelf life with stabilizer (1-2 years)
• Requires kerosene heaters (Sengoku, Toyotomi)
• Less common in stores
• Indoor use requires ventilation

Firewood:

• Cheapest BTU per dollar for many regions
• Requires woodstove or fireplace
• Needs to be properly seasoned (6+ months drying)
• Indoor-friendly with adequate flue
• Long-term storage with proper protection

Wood pellets:

• Cleaner burning than logs
• Easier handling
• Requires pellet stove
• Susceptible to moisture damage
• Less common in some regions

Natural gas:

• Often continues working during electrical outages
• BUT requires electric thermostat for most furnaces
• Generator-powered furnace fan is the key
• No fuel storage required

The carbon monoxide reality

This is the single most important emergency heating safety issue:

Carbon monoxide (CO):

• Colorless, odorless gas produced by incomplete combustion
• Binds to hemoglobin 200x more strongly than oxygen
• Causes brain damage and death rapidly
• Kills 400+ Americans per year from heating equipment
• Symptoms: headache, dizziness, nausea, confusion, unconsciousness
• Detector required in any space with combustion heating

Sources of CO during emergencies:

• Propane/kerosene heaters used indoors
• Generators run in garages or near windows
• BBQ grills used indoors
• Gas stoves used as space heaters
• Charcoal indoors

Safety requirements:

• Battery-powered CO detector (not just smoke detector)
• Adequate ventilation (cracked window or vent)
• Never sleep with unvented combustion heater running
• Generators 25+ feet from any opening
• Never use grills indoors
• Heat one room only (not the whole house)

Shelter-in-place strategy

In severe emergencies, “drift to one room” — heat only a small space:

1. Select a small interior room (no exterior walls if possible)
2. Hang blankets over doors and windows
3. Block drafts at bottom of doors with rolled towels
4. Use small heater sized for the room
5. Sleep in shifts if using unvented heater (someone awake to monitor)

A 12 × 12 ft bedroom (1,152 ft³) at 60°F vs 20°F outside requires only 11,520 BTU/hr with average insulation — vastly less than trying to heat a whole house.

Temperature tolerance for survival

Humans survive at lower temperatures than most people realize:

• 65-70°F: comfortable
• 60-65°F: cool but fine with sweater
• 55-60°F: chilly; needs sweater and movement
• 50-55°F: cold; need multiple layers
• 45-50°F: very cold; risk of mild hypothermia at extended exposure
• 40-45°F: hypothermia risk if wet or inactive
• Below 40°F indoors: serious hypothermia risk

For survival, target 50-55°F minimum indoor temperature. Below this, sleeping risks become serious.

Multi-day power outage timeline

What to expect during prolonged outages:

Day 1: refrigerator items cold, residual heat in walls Day 2: refrigerator warming, freezer still working, residual heat fading Day 3: refrigerator failed, freezer thawing if not frozen solid, indoor temp dropping Day 4: indoor temp ≈ outdoor temp (without heating); food spoiling rapidly Day 7+: long-term emergency requirements

For most US locations, a 3-day outage is the planning threshold. Longer requires substantial fuel storage.

Generator vs heater trade-offs

For backup heat, two main strategies:

Direct heating (propane/kerosene/wood):

• Pros: simple, works without electricity, lower per-BTU cost
• Cons: CO risks, fuel storage logistics
• Best for: rural areas, frequent outages, prepared homeowners

Generator + electric heating (or generator + gas furnace fan):

• Pros: heats whole home, allows refrigeration and lights
• Cons: high fuel use, noise, generator costs ($500-$3000+)
• Best for: shorter outages, suburban homes, those with medical needs

Hybrid approach (most common): generator for essentials (fridge, lights, well pump) + direct heat for primary living space.

Insulation as preparation

Before storing fuel, improve your heat retention:

• Weather stripping doors and windows: $50-100 investment, dramatic difference
• Thermal curtains: blocks heat loss through windows
• Door snakes/draft stoppers: blocks gap at bottom of doors
• Window plastic film: $20-40 per window, reduces heat loss 25%+
• Pipe insulation: prevents frozen pipes
• Outlet/switch gaskets: small leaks adding up

Reducing your home’s heat loss before an emergency = stretching your fuel supply 30-50%.

Common emergency heating mistakes

1. Underestimating fuel needs: 1 day of fuel becomes 24 hours of fear
2. No CO detector: silent killer
3. Whole-house heating: wastes fuel during emergencies
4. Wet firewood: less heat, more smoke
5. Indoor charcoal grill: deadly CO production
6. Sealed room with combustion heater: CO accumulates
7. No backup plan: one method only
8. Old kerosene: degrades over 12-18 months
9. Propane outdoors in extreme cold: tanks freeze, lose pressure
10. No fire extinguisher: needed for any combustion heating

Bottom line

Heat needed (BTU/hr) = Volume × Temperature difference × Insulation factor. For a 200 sq ft room, 40°F temperature difference, average insulation: ~16,000 BTU/hr. Fuel storage for 7 days: 37 gallons propane, 22 gallons kerosene, or 1/4 cord of hardwood. ALWAYS use a battery-powered CO detector with combustion heating. CO from propane/kerosene heaters kills 400+ Americans yearly. Shelter-in-place to one room saves dramatic amounts of fuel. Improving home insulation before emergencies extends fuel supply 30-50%. Target indoor temperature of 50-55°F minimum for survival; comfort starts at 60-65°F. Generator + direct heat hybrid approach handles most emergency scenarios.