The company that pipes natural gas into Portland, Lewiston-Auburn and other parts of southern Maine is seeking a rate increase that would raise the average home’s bill by about $6.

Unitil Corp. says it needs the extra money to offset rising construction costs and other expenses related to distribution. The request isn’t linked to the cost of buying natural gas.

Unitil recently filed its request with the Maine Public Utilities Commission for a $4.6 million increase in its base rate — an increase of 6.3 percent in operating revenue.

If regulators approve the entire request, it will add $6 a month to a yearly home cost of $1,470. That’s the average bill for a home that uses gas for heat, cooking and hot water.

Unitil says that, compared with heating oil, natural gas will remain a good value.

“It’s fair to say that natural gas is roughly half the cost of oil to heat a home,” said Alec O’Meara, a company spokesman. “This rate case is not going to appreciably change that difference.”

Unitil last sought an increase to its base rate in 2011. Some of the money in the current request would go to the operational and safety-related upgrades the company is making in its distribution system.

Unitil is at work on a 14-year project to replace and improve 100 miles of gas lines in Portland and Westbrook — expected to cost at least $60 million.

Unitil has 28,000 gas customers in Maine, where demand for natural gas is growing.

Tux Turkel can be contacted at 791-6462 or at:

tturkel@pressherald.com