you will fail the Heath - Robertson award!
Your are playing the thermosyphon system.
- inlet cold is at bottom
- outlet hot should be at top [ hot water
- no part of the pipe work should be above the water level, it will not flow.
- 1/2 dia. may not allow the water to syphon up.
- 50 ft length may be too long.
- I have seen them with 11/2 inch pipe about 24ft long.
- I use 3/4 Copper as a booster for my hot water off the wood heater and a 6 fy head.