It's common for all fast charging phones. Check your battery temperatures while charging, if its going beyond 45 C then I would suggest to visit Asus Service Center.
Its normal that it will heat while heating. Its not because of Intel processor. Its because of the fast charging technlogy that uses 9V-2A to charge the battery.
Its normal. Even the Samsung Note 4 with fast charging heats while charging.
Even 49 degrees while charging is fine. Don't worry.
Also dont use while charging as battery should not drain more that its charging. It will lead to heating.
Because of FAST Charging, the initial charging is done at 9V/2A current or up to 18W... for the first 60%.... this type of current will defiantly Heat up any Phone...
Also sometimes the Battery is being drained by some Power hungry APP... along with Charging.
Therefore.....
1) Charge it only Once DAY (at night when battery is between 1% to 10%) by continuously charging for 2 Hours till 100% and not charging after every 4-5 hours when battery drops to 40%-50%.
2) Close all the application before charging.
3) Avoid using phone while charging
4) Keep the phone Upside Down (Screen facing down) on a plain surface like Table etc. not on Bed or Clothed surface to expose the backside to air for cooling.