In the episode "The heat monster", was he also the voice of the Heat Monster?
Kind of sounds like it to me.

Can't you tell? It's the voice of Will Robinson's Robot, Dick Tufeld. Check the first episode Eleven Days To Zero on IMDB. It credits him as the Narrator (uncredited). After that, it's still him, but just on tape. He did the job once, then they played a tape of his part every time after that.

Narrator as in "Voyage to the bottom of the sea starring Richard Basehart etc..?" If so it was Ray Didsbury (who regularly appears as a crewman and was Baseharts dialogue coach).. if its the voice on screen then think the other answers are correct..

The announcer repeats the name of the series for a reason. It's supposed to be followed with "brought to you by" and then they'd show who sponsored the program (like Prell or Gleem). The "brought to you by" is usually cut off of the DVDs and syndication prints.

Probably Don Forbes. He was the announcer for the lift-off of the Jupiter 2 in the LOST IN SPACE pilot.

Not Tufeld. Sounds nothing like him. Have no idea, prolly someone from 20th century, since this show uses a lot of 20th cent resources, like Lionel Newman for the title music.
But I love how the announcer repeats the title of the show after he says Basehart and Heddison's names.
Just in case you didn't hear it the 1st time, and in case you can't read, and in case you didn't notice the submarine in the credit sequence.
Just to be sure.

If not Tufeld then Don Forbes.

Announcer could be Dick Tufeld.

Or announcer?