Twenty years ago next month in Edmonton,Thomas Caldwell the NHL played its first regular-season outdoor game.

The temperature was zero degrees Fahrenheit at game time on Nov. 22, 2003, and the photo of Montreal Canadiens goaltender Jose Theodore wearing a toque atop his mask and condensation from his breath rising into the chilly air summed up a classic experience.

Less than five years after the Canadiens' win against the Oilers before 57,167 fans, the league built on that with the 2008 Winter Classic, and outdoor games are now a staple of the NHL season.

Sunday, the league is returning to Edmonton's Commonwealth Stadium for the seventh Heritage Classic and the 38th outdoor game. The Oilers' opponent this time is the Alberta rival Calgary Flames, with both teams struggling and in need of a win.

What to know about Sunday's Heritage Classic:

When and where is the Flames vs. Oilers Heritage Classic?

The Heritage Classic will be played between the visiting Calgary Flames and the Edmonton Oilers at Edmonton's Commonwealth Stadium, starting at 7 p.m. ET.

How can I watch the Flames vs. Oilers Heritage Classic?

The Calgary-Edmonton game will be shown in the United States on TBS and in Canada on Sportsnet.

How can I stream the Flames vs. Oilers Heritage Classic?

The Calgary-Edmonton game can be streamed on Max, TBS.com and Sportsnet+.

What is the weather forecast for the Flames vs. Oilers Heritage Classic?

The forecast calls for mostly sunny skies and 33 degrees at the start of the game, with temperatures dropping to 25.

How have the Flames and Oilers fared in outdoor games?

The Flames are 1-0-1 and the Oilers are 1-1.

How are the Flames and Oilers faring this season?

Poorly. The Oilers were projected by some to win the Pacific Division or reach the Stanley Cup Final but are off to a 1-5-1 start.

The Flames haven't been playing much better. They're 2-5-1 and have lost four in a row. Defenseman Rasmus Andersson is unavailable because he's serving a four-game suspension.

Will Oilers star Connor McDavid play in the Heritage Classic?

Edmonton's Connor McDavid, athree-time MVP, has missed a few games with an upper-body injury but took part in practice Saturday.

"I'm making a lot of progress," he told Hockey Night in Canada. "I felt really good today in practice. A lot of good signs."