This story was updated at 2:02 p.m. to reflect corrected information from Unitil

Greater Portland’s natural gas supplier has filed a petition with the Maine Public Utilities Commission requesting approval to increase its distribution base rates.

Unitil Corp. said proposed rates would increase on average by $7.79 for a residential, nonheating customer, and $16.91 per month for a residential heating customer. For heating customers, this represents a 19.7 percent hike in annual heating costs.

An average home customer who heats with natural gas and uses 70,000 cubic feet a year now pays $1,060, according to Unitil.

Unitil said the last change in its gas distribution base rate for Maine customers occurred 28 years ago. Even if the company’s full request is approved by the PUC, rates will remain below 2008 levels, when supply costs were higher, the company said.

The increase would bring rates in line with current operating expenses and continuing investments in safety-related facilities and equipment, the company said. The new rates will help fund the recently begun effort to replace and upgrade more than 100 miles of pipe in Portland and Westbrook. The 14-year project, estimated to cost $60 million, will remove all cast-iron pipe from the local distribution system and modernize the system, allowing for further growth in the utilization of natural gas.

“Natural gas bills are currently at a five-year low for our customers, thanks to lower supply costs,” said Alec O’Meara, Unitil’s spokesman. “After this proposed rate increase occurs, natural gas will still remain a safe, highly affordable option for our customers when compared to other fuels.”

Hampton, N.H.-based Unitil bought Northern Utilities in 2008. It has 28,000 customers in Maine.