PITOT HEAT.......The Pitot Head is so positioned to enable dynamic pressure to show Indicated Air Speed. It does this by pressure variation within the instrument, the faster the greater pressure the higher IAS. Slowing down will reverse the effect.
Pitot heat is provided to ensure that the air within the pipes/instrument is unhampered by the restricyion that will result should icing occur. Static pressure port is either part of the Pitot Head or as a separate port elsewhere.
The pitot heat generally is unlikely to heat up all of the trapped air which is within the system and therefore unlikely to have any 'mechanical' effect upon the IAS reading. There are other effects which will effect the rading. Flying out of ballance, whether climbing or descending, accellerating or deaccellerating.
In your Flight Manual, in the Performance Section there will be a Airspeed Calibration Curve (level flight) chart which shows the relationship between IAS and Calibrated Airspeed(CAS). IAS corrected for position error equals CAS.
To my knowledge there are no charts or data for helicopters below 2835kg AUM which suggests that pitot heat has an effect in IAS.