SOUTH BOSTON, Mass. (WHDH) — It’s challenging enough to stay cool during the heat wave – but four-thousand people were without power in Boston Wednesday night.

The lights were back on in South Boston Thursday morning but a blackout there meant a lot of people didn’t have air conditioning Wednesday night and early Thursday.

A manhole explosion had NStar crews working into the night in South Boston.

That explosion happened late Wednesday night on West First Street, between B and C streets.

Crews said the explosion did not cause a fire and no one was hurt – but it did knock out power for neighbors.

According to NStar, the issue may have been related to more people using power, during the heat wave.

In the meantime, ISO-New England predicted power usage Thursday could be the highest it’s been in nearly seven years.

ISO-New England said the one-day record for power use is more than 28,000 megawatts, which was set in August of 2006.

Officials believed the region could come close to that on Thursday.

ISO-New England had some tips to conserve energy during the heat wave.

Conservation Tips

-Raise AC thermostats to between 74-78 degrees

-Turn off unneeded lights between 12pm-8pm

-Put off laundry & chores until early morning/late evening, when the demand for energy is often lower

The heat wave has also been producing smog and unhealthy air that may continue into the weekend.

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