![[Pasted image 20250614094628.png]] # MVP Ground Hot Tub - Bare Minimum Build ## Goal Prove that a fire-heated ground hot tub works for under $400 ## Shopping List - **EPDM pond liner** (10'x10') - $200 (cheapest you can find) - **3/4" copper pipe** (50 feet) - $100 - **2 SharkBite copper-to-PEX adapters** - $25 - **3/4" PEX** (20 feet) - $20 - **Metal trash can or old drum** (for fire) - $0-30 - **Rocks** (from property) - $0 **Total: ~$345-375** ## Build Day 1 (4 hours) 1. **Dig hole**: 6' wide, 4' deep 2. **Shape rough bench**: 2.5' deep ledge 3. **Carve groove**: For pipe path down wall 4. **Smooth bottom**: Remove sharp rocks ## Build Day 2 (3 hours) 1. **Lay liner**: Just drop it in, press down 2. **Make coil**: Bend copper into spiral (trash can as form) 3. **Connect pipes**: - Copper to PEX at rim - PEX down groove to bottom - PEX for hot return near surface 4. **Weight edges**: Rocks around perimeter 5. **Fill**: Garden hose, 2-3 hours ## First Fire Test - Put coil in/around fire container - Light fire - Check if water circulates (feel for hot spot) - Monitor temp with kitchen thermometer - Should hit 100°F in 3-4 hours ## What You're Testing - Does thermosiphon actually work? - How much wood does it take? - How long to heat up? - Does it hold temperature? - Any leaks? ## If It Works Then invest in: - Better fire ring - Insulation cover - Nicer rocks - All the aesthetic stuff ## If It Doesn't Work You're only out $350 and a weekend of digging ## Bare Minimum Operation - Heat weekly to 160°F to kill bacteria - Drain after 1-2 weeks use - Refill as needed - Cover with tarp when not in use That's it. No frills. Just proving hot water can happen.