"It's basically an accordion with a keyboard and a pump that you operate with your feet. These were very cheap and very easy to mass produce, and thousands of them were brought into New Zealand.
"In colonial times, if a family had an instrument, it was one of these. They were actually cheaper than a piano."
There is a date on the organ - 1906 - but Mr Newton said that wasn't necessarily accurate. He said it was typical of American reed organs that were produced between 1880 and around 1910.
He said the St Paul's organ would not need much work to be in good order again.
"It needs a good clean. There's been no moth damage to the velvet or the leather - that could have been very serious. Mice have eaten part of the wood, but the bellows are still intact."
Mr Newton travels the country restoring organs. He specialises in pipe organs, and has 80 scattered around the country that he maintains.
Since 2011, he's been doing a lot of recovery work on organs in Christchurch, including moving organs from earthquake-damaged churches into safe storage.
Huia Kirk from the church's restoration trust said the history of the organ in relation to the church was not known. She believed it was donated to the church in the 1970s.
"It's really on its last gasp, and hasn't been played for a long time. As far as we know, no maintenance has ever been done on it."
Ms Kirk said restoring the organ was part of a big programme of restoration happening at the church, which dates from 1937. The church fundraised for five years to make the restoration possible.
So far, leaks have been fixed, there's been a new roof, new wiring, an alarm and sprinkler system installed, piles checked and the exterior painted.
"Next year we want to repaint the interior, put in new fittings for the vestry and install new toilets," Ms Kirk said.