Above ground, a 7,855-pipe organ is one of the great splendors of St. Patrick’s Cathedral on Fifth Avenue, the luminous church that will be the heart of the action in New York on St. Patrick’s Day. But hidden below the cathedral’s floor, a new system of pipes just as intricate is a source of equal pride.

A year ago, as part of its nearly $200 million renovation, St. Patrick’s Cathedral launched a state-of-the-art geothermal heating and cooling system to replace its system of steam radiators and 1960s-era air conditioning. Around the cathedral’s perimeter are now 10 wells as deep as 2,200 feet into the Manhattan bedrock, collecting groundwater that helps the church efficiently heat and cool. The cathedral now reaches six times deeper than its Gothic spires soar high.

The system’s thousands of feet of pipes and dozens of pumps are invisible to the five million visitors to the cathedral each year, and that was the point. The trustees of the 138-year-old building, the centerpiece of the Roman Catholic Archdiocese of New York, wanted the church to appear as it always has, even as it was going green.