Plumbing Your Tiny Home: Water In, Waste Out

Plumbing in a tiny home follows the same principles as conventional construction, just in a tighter package. The key challenge: routing pipes through minimal wall and floor cavities while maintaining proper slope on drains.

Water Supply System

Choosing Your Water Source

• City water connection: Most reliable. Use a standard hose bib with pressure regulator.
• Well water: Requires a pump and pressure tank.
• Water tank (mobile): 40-100 gallon fresh water tank for THOW builds.

Supply Line Materials

PEX tubing is the best choice for tiny homes:

• Flexible — routes through tight spaces easily
• Freeze-resistant — expands without bursting
• Easy connections — crimp or push-fit fittings, no soldering
• Color-coded — Red for hot, blue for cold

Installation Steps

1. Plan your layout — shortest runs possible from water heater to fixtures
2. Install a main shutoff valve at the water entry point
3. Run a cold manifold near the water heater
4. Branch to each fixture with individual shutoff valves
5. Insulate all hot water lines and any cold lines in exterior walls
6. Pressure test at 80 PSI for 30 minutes before closing walls

Drain-Waste-Vent (DWV) System

The Critical Rule: Gravity

Drain pipes must slope downward at 1/4" per foot. In a tiny home, this means careful planning to avoid conflicts with the trailer frame or floor joists.

Pipe Sizing

• Toilet drain: 3" PVC
• Shower/tub drain: 2" PVC
• Sink drain: 1.5" PVC
• Vent stack: 1.5" or 2" PVC through the roof

Venting Options

Every drain needs venting to prevent siphoning of the trap seal:

1. Traditional vent: Pipe through the roof (best but requires roof penetration)
2. Air Admittance Valve (AAV): Mechanical one-way valve under the sink (check local code — not accepted everywhere)
3. Studor vent: Brand name AAV, widely used in tiny homes

Hot Water Solutions

Option	Pros	Cons
Tankless electric	Compact, endless hot water	High amperage draw
Tankless propane	No electrical load, fast recovery	Requires gas line and venting
Small tank (6-10 gal)	Inexpensive, simple	Runs out quickly
Heat pump hybrid	Most efficient	Too large for most tiny homes
Woodstove water jacket	Free heat, dual-purpose	Seasonal, requires fire tending

For most tiny homes, a tankless propane unit offers the best balance of performance and space efficiency. For off-grid builds with a woodstove, read on — the hydrosyphon system below is a game-changer.

Hydrosyphon Shower System: Using Your Woodstove for Hot Water

If you're building off-grid and your woodstove is your primary heat source, a thermosyphon (hydrosyphon) hot water system gives you free hot water with zero electricity and zero pumps. This is one of the most elegant off-grid plumbing solutions that exists.

How Thermosyphon Works

The principle is simple: hot water rises, cold water sinks. By connecting a water coil inside or around your woodstove to an elevated storage tank, water circulates naturally without any pump.

1. Cold water sits in the bottom of an insulated storage tank mounted above the woodstove
2. A supply line runs from the tank bottom down to a heat exchanger coil in the woodstove firebox (or wrapped around the flue pipe)
3. The fire heats the water in the coil
4. Hot water naturally rises through a return line back to the top of the tank
5. This creates a continuous convection loop — no moving parts, no electricity

Critical Design Requirements

Tank placement: The bottom of your hot water tank must be at least 12-18 inches above the top of the woodstove heat exchanger. More height difference = stronger flow. This is the gravity that drives the entire system.

Pipe sizing: Use 3/4" copper or stainless steel for the circulation loop. Never use PEX near the woodstove — it will melt. The supply and return lines must be copper or stainless from the stove to at least 3 feet away, then you can transition to PEX.

No dips or traps in the loop: The pipe run from stove to tank must rise continuously. Any dip creates an air lock that kills circulation. Plan your route carefully.

Pressure relief is mandatory: Install a temperature and pressure (T&P) relief valve on the tank. Thermosyphon systems can overheat if the fire is very hot and no water is being drawn. A T&P valve prevents a dangerous pressure buildup. This is not optional — it is a critical safety component.

Building the Heat Exchanger

Option A — Firebox coil: Wrap 15-20 feet of 3/4" copper tubing into a flat coil and place it inside the firebox, against the back wall. This gives the most direct heat transfer. Use high-temperature stove cement to seal the pipe penetrations through the firebox wall.

Option B — Flue pipe wrap: Wrap copper tubing in a tight spiral around the first 3-4 feet of flue pipe above the stove. This is less efficient but easier to install and doesn't require modifying the firebox. Use hose clamps and high-temp silicone to secure the coil.

Tank Sizing and Insulation

• A 20-30 gallon tank is ideal for a tiny home thermosyphon system
• Use a stainless steel or glass-lined tank (never bare steel — it rusts)
• Insulate the tank heavily — minimum R-12 wrap. The better you insulate, the longer your hot water lasts after the fire dies
• Include a cold water inlet at the bottom (with a check valve) and a hot water outlet at the top

Shower Setup

With a well-designed thermosyphon and a 30-gallon tank, you can expect:

• Water temperatures of 110-140°F when the stove is running (use a thermostatic mixing valve to prevent scalding)
• Two full 8-minute showers from a full tank
• Hot water available 30-45 minutes after lighting the fire
• Water stays warm for 4-6 hours after the fire goes out (with good insulation)

Seasonal Considerations

The thermosyphon system is inherently seasonal — it works when you're running your woodstove. For summer hot water, pair it with one of these:

• A solar batch heater (black-painted tank in a glazed box) for sunny days
• A small propane tankless heater as a backup
• An outdoor solar shower bag for warm months

Composting Toilet Option

Eliminates the need for a black water drain entirely:

• No water usage for flushing
• No holding tank needed
• Legal in most areas when paired with an approved gray water system
• Requires regular maintenance and emptying

Gray Water Management

If you're off-grid or on a trailer, you'll need a gray water solution:

1. Portable gray water tank: 20-40 gallons, dump at an RV station
2. Gray water recycling: Filter and reuse for irrigation (check local laws)
3. Sewer connection: If on a permanent site, connect to municipal sewer or septic

Winterization

Tiny homes are especially vulnerable to frozen pipes:

• Insulate all supply lines, especially in the floor cavity
• Install heat tape on vulnerable runs
• Keep interior temps above 50°F
• Know how to drain the system completely for extended cold snaps