District Heating
District heating distributes hot water from a central source to multiple buildings through insulated underground pipes. It is one of the most efficient ways to heat a community — a single large, well-tended fire heats an entire village, replacing dozens of individual stoves and fireplaces. The technology has been used since Roman times (hypocaust systems), and modern district heating networks serve entire cities across Scandinavia, Russia, and Eastern Europe. For a post-collapse village of 30-150 people, it dramatically reduces total fuel consumption, fire risk, and labor.
Why District Heating
Efficiency Gains
Compared to individual household heating:
- Central boiler efficiency: 80-90% (large, well-designed, professionally operated)
- Individual stove efficiency: 40-70% (variable, often poorly operated)
- A village of 30 homes using individual wood stoves might burn 150 tonnes of wood per winter
- The same village on district heating might burn 80-100 tonnes — a 30-50% savings
- One skilled boiler operator replaces 30 households tending individual fires
Safety
- Eliminates 30 individual fire sources (the leading cause of structure fires)
- No smoke or CO risk inside individual homes
- No fuel storage at each house (reduces fire load)
- Children and elderly are safer without open flames in living spaces
System Architecture
Basic Layout
A district heating system consists of:
- Central plant: Where fuel is burned and water is heated
- Supply pipe: Carries hot water (70-90°C) from the plant to buildings
- Return pipe: Carries cooled water (40-60°C) from buildings back to the plant
- Building connections: Each building has a heat exchanger or direct connection to the loop
- Circulation pump: Moves water through the system (can be gravity-assisted with elevated tank)
Supply & Return Layout
Two-pipe system (standard):
- One supply pipe, one return pipe, running in parallel
- Buildings connect in parallel (each gets full supply temperature)
- Most flexible — each building is independent
Single-pipe loop (simpler):
- One pipe loops through all buildings in series
- Each building extracts heat, so temperature drops along the loop
- First building gets hottest water, last building gets coolest
- Only practical for small systems (5-10 buildings) with low heat extraction per building
Design Temperature
- Supply temperature: 70-90°C (higher for radiator heating, lower for underfloor)
- Return temperature: 40-60°C
- Temperature drop (delta-T): 20-30°C across each building’s heat exchanger
- Higher delta-T means smaller pipe sizes (less water flow needed) but requires larger heat exchangers
Central Heat Source
Wood-Fired Boiler
The most likely fuel source for a post-collapse village:
Design features:
- Fire tube boiler: Fire and hot gases pass through tubes surrounded by water. Simple construction, efficient heat transfer
- Water jacket: The firebox is surrounded by a water-filled jacket. As fire burns, water heats. Simplest design
- Thermal mass: Surround the boiler with brick or stone to store heat between fire sessions. A large masonry boiler can maintain output for hours after the fire dies
Construction:
- Build a firebox from firebrick (internal dimensions: 60 × 60 × 100 cm for a 30-building system)
- Surround with a water jacket made from welded steel plate (or adapt a large steel tank)
- Route exhaust gases through steel tubes passing through the water tank (increases heat extraction)
- Chimney creates draft for combustion air
- Feed water connections: cold return enters at the bottom, hot supply exits at the top
Sizing: Approximately 3-5 kW of thermal output per connected building (well-insulated small homes in temperate climate). A 30-home system needs 90-150 kW boiler capacity — achievable from a single large firebox burning 10-20 kg of wood per hour.
Multi-Source Integration
The central plant can accept heat from multiple sources:
- Biogas boiler: Supplemental burner using community biogas
- Solar thermal: Large collector array pre-heats return water before the boiler
- Concentrated solar: Parabolic trough directly heats the supply water in summer (may eliminate need for burning fuel in summer months)
- Waste heat: From workshops (forge, kiln, bakery) or future power generation
Distribution Network
Pipe Materials
| Material | Max Temp | Durability | Availability | Notes |
|---|---|---|---|---|
| Steel pipe | 200°C+ | 30-50 years | Salvage, wells, plumbing | Best for main trunks. Needs corrosion protection |
| Copper pipe | 200°C+ | 50+ years | Salvage from buildings | Expensive but excellent. Use for building connections |
| HDPE plastic | 80°C | 30+ years | Salvage from water/gas mains | Good for low-temp systems. Butt-fused joints |
| Clay pipe | 100°C | 100+ years | Can be manufactured | Traditional. Heavy, fragile, but fireproof and permanent |
| Wooden pipe (bored log) | 80°C | 10-20 years | Manufactured | Historical. Suitable for short-term or low-pressure |
Insulation
Pipe insulation is critical — without it, most heat is lost in transit:
- Minimum insulation thickness: 5 cm for short runs (<50 m), 10 cm for longer runs
- Materials: Fiberglass batting, mineral wool, rigid foam (salvaged building insulation), or packed straw in a wooden trough
- Moisture protection: Wrap insulation in plastic sheeting or a waterproof outer pipe. Wet insulation loses all effectiveness
Burial
- Bury pipes 60-100 cm deep (below frost line in cold climates)
- Lay supply and return pipes in the same trench, 15-30 cm apart
- Bed in sand or fine gravel (protects from rock damage)
- Mark the trench route for future access
Expansion
Water expands when heated. The system needs:
- An expansion tank at the highest point (open to atmosphere, or closed with an air cushion)
- Expansion loops in long pipe runs — a U-shaped detour that absorbs pipe expansion without stressing joints
- Air vents at high points to prevent air locks that block circulation
Building Connections
Heat Exchanger
Each building ideally has a heat exchanger separating the district loop from the building’s internal heating:
- Plate heat exchanger (if salvageable from HVAC equipment): Most efficient, compact
- Coil-in-tank: A coil of copper pipe from the district loop immersed in the building’s water tank. Simple and effective
- Direct connection (simplest): District water flows directly through the building’s radiators. Simpler but a leak in any building drains the whole system
Radiators & Underfloor Heating
- Radiators: Salvaged from buildings. Standard hot water radiators work perfectly. Mount below windows for best heat distribution
- Underfloor heating: Pipes embedded in a concrete or earthen floor. Lower water temperature needed (35-45°C). Most comfortable heating method. Must be installed during construction
Domestic Hot Water
District heating also provides domestic hot water (bathing, washing):
- A small heat exchanger or coil in an insulated tank at each building
- District water heats the domestic tank to 55-65°C
- This eliminates the need for individual water heating in each home
Operation
Fuel Consumption
For a village of 30 well-insulated homes in a temperate climate (heating season: October-April, ~200 days):
| Heat Source | Annual Fuel | Labor |
|---|---|---|
| Wood (coppiced hardwood) | 80-120 tonnes | 2-3 hours/day fire tending |
| Coal (if available) | 50-80 tonnes | 1-2 hours/day |
| Wood + solar thermal | 50-80 tonnes | 1-2 hours/day (summer free) |
| Biogas supplement | Reduces wood by 15-25% | Digester maintenance |
This wood can be sustainably supplied from 10-20 hectares of managed coppice.
Circulation
Water must circulate continuously when the system is operating:
- Gravity circulation (thermosiphon): If the boiler is lower than the buildings and piping is properly sloped, hot water rises naturally. Works for small systems (5-10 buildings) with short pipe runs
- Pump: For larger systems, a circulating pump is needed. A small electric pump (50-200 watts) driven by hydro or wind power. Or a mechanical pump driven by a waterwheel
Expanding the Network
District heating is inherently expandable:
- As the village grows, extend the pipe network to new buildings
- Upsize the boiler or add a second boiler when demand exceeds capacity
- Add seasonal thermal storage (underground tank — see heat-storage-systems) to bridge peak demand
See Also
- heat-storage-systems — Thermal storage for overnight and peak demand
- coppicing-fuel-management — Sustainable fuel supply for the boiler
- biogas-digesters — Supplemental heat source from waste
- solar-thermal-collectors — Free summer heating
- micro-hydro-turbine — Power for circulation pumps
Getting Started: Pilot System
Before committing to a full village network, build a pilot system connecting 3-5 adjacent buildings:
- Choose buildings close together (within 50 meters of the heat source) to minimize pipe runs
- Use a simple boiler: A large wood stove with a water jacket, or a 200-liter drum with a fire tube through it
- Run above-ground insulated pipes (temporary — faster to install and debug). Wrap with straw bundles and plastic sheeting
- Direct connection (no heat exchangers for the pilot — simpler)
- Gravity circulation if the boiler can be positioned lower than the buildings; otherwise a small 12V pump powered by a battery
The pilot system lets you:
- Measure actual heat loss per meter of pipe
- Determine how much fuel the boiler consumes per degree of supply temperature
- Test circulation rates and pressure drops
- Identify problems (air locks, expansion issues, leak points) before scaling up
- Build community buy-in — once people feel the warm radiators, support for the full system builds itself
Timeline: A pilot system for 3-5 buildings can be built in 2-3 weeks by a team of 4-6 people with basic plumbing skills. The full village system then takes 2-3 months of construction, primarily trenching and pipe laying.