The quick scoring rate of Redmond's runs from 50 to 100 was a surprise to a habitually defensive batsman.
"It definitely wasn't the plan, but sometimes things just click," he said. "I didn't even realise I scored it that quickly. You just have to give yourself a bit of time early on, and then you have the chance to bat for two or three hours.
"It always helps to spend time at the crease - gives you that bit of confidence."
It was Redmond's sixth century in first class cricket. After sharing century stands with his fellow opener Peter Fulton (57) and captain Brendon McCullum (72), Redmond (121) could afford a degree of satisfaction.
As for England, Redmond knows New Zealand are up against world-class opponents.
"They're great bowlers, who've played a lot of Test cricket," he added. "For a new guy like me coming through, you can't get caught up with that - you've just got to keep it simple and believe in yourself."
He needed great care over his first 50 at Wantage Road but then raced to three figures in only 64 more balls - hitting 19 fours and a six in all.
Northants change seamer Dave Wigley finished with flattering figures of four for 74 as the Kiwis ran out of steam late on.