What recommendations are there in regards to using a fan/air conditioner/air circulator in the baby’s room to deal with the summer heat?

Red Nose has the following information in relation to dressing baby, particularly on hot days.

Dress your baby as you would dress yourself for the temperature of the room – comfortably warm, not too hot, not too cold.
In warmer weather, you can dress baby in a sleeveless and legless onesies, or just a nappy and singlet.
For cooler weather, a full suit will keep baby warm.

We don’t believe that it’s necessary to use a room temperature monitor, or to leave the heating or cooling on all night,
as long as baby is dressed appropriately for the temperature of the room – not too hot, not too cold.

An oscillating fan positioned away from the cot can help during the hotter months.
Fans circulate the air and also provide white noise for baby, which can help them sleep more soundly.
https://rednose.org.au/article/how-to-dress-baby-for-sleep