HEAT is basically always going to be a premium round variant (like APCR for many tanks) of a tank's shells. It'll have higher penetration than standard rounds.
It's similar to HE in that both shells are unable to go through destructible objects like fences. Additionally, both of these shell types benefit from the additional boost to penetration provided by Calibrated Shells when compared to the standard AP and APCR shell types. HEAT also doesn't lose penetration over distance like APCR and AP.
It struggles with spaced armor like HE and it can bounce like AP and APCR shells, doing 0 damage. It will not splash like HE.
I'll add that I often find premium rounds are worth the extra cost. Penning more shots per game can definitely turn a loss into a win. Just be smart about it, weigh the risks of aiming harder with doing less damage. Make sure you purchase them with credits, not gold, by pressing that button near the ammo selection indicators to switch currency types.
Edited by Ronin_23, 21 July 2020 - 08:23 PM.