The boyband are the highest new entry, coming in at number five between Emma Watson and Adele. The singer rose ten places to sixth in this year's rankings.
One Direction are estimated to have earned a collected £26,330,000.
Harry Potter star Daniel Radcliffe retains his place at the top of the list, having earned an estimated £53.33 million
Heat editor Lucie Cave commented: "In these financially tough times it's good to know that at least somebody is rolling around on carpets woven from gold-plated £50 notes - which is why Heat is delighted to reveal our annual countdown of the richest British celebs under the age of 30.
"One Direction will be thrilled to hear that they've burst into Heat's Rich List as the highest new entry at number five.
"Like any popstars they'll be after the number one spot, of course, but if they keep going the way they have been, that might be a reality in 2013."
The full Heat Rich List 2012 for the under-30s
Copyright: PA Images Julien Behal/PA ArchiveThe top ten is as follows:
1. (1) Daniel Radcliffe - £53.33 million
2. (3) Robert Pattinson - £38.733 million
3. (2) Keira Knightley £32.7 million
4. (4) Emma Watson £26.533 million
5. (NE) One Direction £26.330 million
6. (16) Adele - £26.066 million
7. (5) Rupert Grint £23.466 million
8. (6) Leona Lewis £13.66 million
9. (7) Cheryl Cole £13.4 million
10. (8) Katie Melua £11.066 million
When bands only are considered, Girls Aloud collectively top the mini-list, followed by One Direction, JLS, The Saturdays and The Wanted.
In the US, the list is topped by the Olsen Twins, followed by Britney Spears, Lady GaGa, Justin Bieber and Miley Cyrus.
The full list appears in this week's Heat magazine, complete with special live augmented reality content, on sale now (Tuesday, October 23).