# Pipe Rail Heating

> Glossary term · [DutchGreenhouses glossary](/glossary.md)

Pipe rail heating is the floor-level circuit between crop rows that heats the greenhouse and doubles as rails for harvest trolleys. The 51 mm pipe — the “51’er” — was drawn for horticulture rather than taken from standard steel sizes, and dates to Jaap Zegwaard’s 1968 system.