Heat Reflection

Part of Emergency Shelter

A fire alone wastes most of its heat into the sky. A fire wall bounces that energy back toward you, and heated rocks store it for hours after the flames die. Together they can make a basic shelter livable in freezing conditions.

The Problem With Open Fires

An open campfire radiates heat in all directions equally. Sitting next to one, you receive roughly 15-20% of its total heat output. The rest goes into the ground, the sky, and the air behind the fire. A simple reflector wall can redirect another 20-30% of that wasted energy toward your shelter, effectively doubling the heat you receive.

Fire Walls (Reflector Walls)

A fire wall is a vertical barrier placed on the far side of your fire, opposite your shelter. It reflects radiant heat back toward you.

Basic Log Fire Wall

The simplest and most effective design:

1. Drive two pairs of stakes into the ground about 90-120 cm (3-4 feet) apart, on the far side of your fire pit. Each pair should be about 15 cm (6 inches) apart, creating a channel for logs to stack between.

2. Stack green logs horizontally between the stake pairs. Use logs 8-15 cm (3-6 inches) in diameter. Stack them 60-90 cm (2-3 feet) high.

3. Angle the wall slightly — lean the top toward the fire by 10-15 degrees. This angles the reflected heat downward toward your sleeping position rather than over your head.

4. Wall width: At minimum, the wall should be as wide as your shelter opening. Wider is better — 120-180 cm (4-6 feet) is ideal.

Distance from fire: Place the wall 30-45 cm (12-18 inches) behind the fire. Too close and it burns; too far and reflection is weak.

Use Green Wood Only

Dry, dead wood for the reflector wall will eventually catch fire. Use freshly cut green logs. They will char on the fire-facing side but will not ignite. Replace charred logs every few days in a long-term camp.

Stone Fire Wall

Where rocks are available, a stone wall is more durable and actually stores heat:

1. Select dense, dry rocks: Granite, basalt, and sandstone work well. Avoid river rocks and any stone that has been submerged — trapped moisture can cause explosive fracturing when heated.

2. Build a dry-stack wall 60-90 cm (2-3 feet) high. Angle it slightly toward the fire.

3. Use flat stones for the face: Flat surfaces reflect heat more efficiently than rough, irregular surfaces.

4. Chink gaps with mud or clay: This prevents heat from passing through the wall and improves reflection.

Wall Type	Heat Reflection	Heat Storage	Durability	Build Time
Green log	Good	Low	Days	30-45 min
Dry stone	Good	High	Months	1-2 hours
Mud/clay on frame	Excellent	Medium	Weeks	2-3 hours
Stone + mud plaster	Excellent	High	Months	2-3 hours

Advanced: Parabolic Reflector Shape

Instead of a flat wall, curve the reflector slightly inward (concave toward the fire). This focuses reflected heat toward a specific point — your sleeping area. The curve does not need to be precise. Even a rough crescent shape, 150-180 cm (5-6 feet) wide and curving 20-30 cm (8-12 inches) inward at the center, significantly concentrates heat.

Rock Heat Sinks

Rocks absorb heat slowly and release it slowly. A heated rock continues radiating warmth for 4-8 hours after the fire dies. This is your overnight heating system.

Heated Rock Bed

This technique places heated rocks beneath your sleeping insulation:

1. Build your fire directly on the ground where you plan to sleep. Let it burn for 2-3 hours to heat the earth beneath.

2. While the fire burns, heat additional fist-to-head-sized rocks around the fire perimeter. Dense, dark rocks absorb heat best.

3. Rake away the fire and coals. Sweep the heated ground clean.

4. Place heated rocks in a single layer where your torso will rest (from shoulders to hips — warming your core matters most).

5. Cover with 8-10 cm (3-4 inches) of earth or sand, then add your normal ground insulation on top. The earth layer prevents burns and distributes heat evenly.

6. Lie down and sleep. The rocks will radiate warmth upward for 4-8 hours.

Rock Safety

• Never use river rocks or wet rocks near fire. Trapped water turns to steam and can shatter the rock violently.
• Test rocks before relying on them: Tap two rocks together firmly. A clear ring means solid and safe. A dull thud may indicate fracture planes or porosity.
• Always use a soil buffer between heated rocks and your body. Direct contact with fire-heated rock will burn skin.

Personal Heat Stones

For supplemental warmth during the night:

1. Heat smooth, dense stones (roughly fist-sized) at the fire’s edge for 30-60 minutes
2. Wrap each stone in multiple layers of cloth, grass, or bark
3. Place near your core: between thighs, against abdomen, or under armpits
4. Replace wrapping if it scorches — this means the stone is too hot for direct use
5. A well-heated stone stays warm for 2-4 hours

Long Fire (Sustained Heat Through the Night)

A long fire is an alternative to rock heat sinks when you need continuous warmth:

1. Find or cut two green logs at least 15 cm (6 inches) in diameter and 180-200 cm (6-7 feet) long
2. Lay them parallel with a 10-15 cm (4-6 inch) gap between them
3. Fill the gap with tinder and kindling, then light
4. The fire burns slowly along the length of the gap, consuming the inner faces of the logs
5. A well-built long fire burns 6-8 hours with minimal tending

Place your fire wall behind the long fire and sleep on the opposite side, 60-90 cm (2-3 feet) away.

Positioning: The Complete Thermal Setup

The optimal arrangement combines shelter, fire, and reflector:

        [WIND DIRECTION →]

   ┌─────────────────────┐
   │   SHELTER (low roof) │
   │   YOUR SLEEPING SPOT │
   └─────────────────────┘
          60-90 cm gap
   ═══════════════════════  ← Fire (long fire or standard)
          30-45 cm gap
   ███████████████████████  ← Fire wall / reflector

• The shelter opening faces the fire
• The fire wall is on the far side of the fire
• Wind hits the fire wall first (it acts as a windbreak too)
• Heat reflects off the wall, through the fire, and into your shelter
• The low shelter ceiling traps warm air at body level

Material Alternatives for Reflectors

If you have salvaged materials, these improve reflection significantly:

• Aluminum foil or emergency blankets: Reflect up to 95% of radiant heat. Attach to the inside of your fire wall or shelter ceiling.
• Sheet metal: Excellent reflector. Bend into a curve for focused heat.
• Wet mud plaster on a wall: Dries to a smooth surface that reflects heat better than rough wood or stone.
• Vehicle windshield sun shades: Designed specifically for heat reflection.

Key Takeaways

• A fire wall doubles the heat you receive from a campfire by reflecting wasted energy back toward you
• Angle the reflector wall 10-15 degrees toward the fire so heat directs downward to your sleeping level
• Rock heat sinks provide 4-8 hours of warmth after the fire dies — place heated rocks beneath a soil buffer under your bedding
• Never use river rocks or wet rocks near fire — trapped moisture causes explosive fracturing
• Position shelter, fire, and reflector wall in a line with wind hitting the reflector first