Over the whole year the average is about 24 to 25°C. These are averages for the month, so the middle of a summer day is hotter.
The hot months are also dry. The dry season runs from January to September, and the air is driest in June and July.
The heat shows on the electricity bill. It runs 500,000 to 2,000,000 VND a month, and the air conditioning decides almost all of it.