The blast last Monday forced drillers using the pipe to reduce output in the Marcellus and Utica shale in Pennsylvania, Ohio and West Virginia, the nation's biggest gas producing region, during the week before a polar vortex is expected to freeze the eastern half of the United States.

Total output in the Marcellus and Utica returned to 30 billion cubic feet per day (bcfd), the same as before the pipe blast, which cut production there by around 1 bcfd last week, according to financial data provider Refinitiv.

One billion cubic feet is enough gas for about 5 million U.S. homes for a day.

TETCO told customers in a notice late Sunday that it increased capacity on a couple of lines around the blast site, but could not say when it would restore full service through the area.

Those flows will help deliver much-needed fuel to utilities in the U.S. Midwest as temperatures plunge later this week, boosting gas demand to a forecast daily record high, according to Refinitiv data.

Before the Jan. 21 blast, which injured two people and damaged three homes near Summerfield in Noble County in southeastern Ohio, about 1.2 bcfd of gas was flowing south on TETCO from Ohio toward the Gulf of Mexico, according to Refinitiv.

After the explosion, however, TETCO started moving up to 0.3 bcfd of gas north into Kentucky and Ohio. But with southbound service restored through parts of the Ohio blast site, about 0.3 bcfd was expected to flow south on the pipeline on Monday.

Enbridge said the damaged section of 30-inch (76.2-cm) pipe was built in 1952-53.

The 9,029-mile (14,531-km) TETCO pipeline was designed to carry gas from the U.S. Gulf Coast and Texas to high-demand markets in the mid-Atlantic and Northeast, according to the company's website.

TETCO became bidirectional over the past five years, enabling it to also carry gas from the Marcellus and Utica shale, where production is growing rapidly, to markets in the U.S. Midwest and Gulf Coast.

(Reporting by Scott DiSavino; editing by Jonathan Oatis)