How to Reduce Current Harmonics in SSR Phase Angle Control for 1000W Heater Load?

Hi, I have pure resistive heater load which consumes 1000W to deliver power to heat a liquid. To constantly generate 1000W at multiple voltages, I have implemented a Solid State Relay (SSR) based firing angle control mechanism to deliver AC supply to the heater. This circuit and logic is working fine. However, this method is leading to lot of current harmonics in the multiples of 50Hz and 60Hz which are its operating frequencies. How can I reduce the harmonics? I am performing a cycle by cycle phase angle control of the AC to deliver power to heater. I have used an SSR with built in snubber circuit. Also I have a line filter on the AC input line to reduce overall emissions. Operating voltage in my case is 100VAC to 240VAC and 16A current. Need ideas that can be implemented like soft start (with cycle by cycle control) or suppress harmonics. 

Arun phase angle control at high powers does generate a lot of interference and harmonics.  What you should consider is burst-fire power control which only lets complete half cycles through to the load.  You can still achieve pretty precise control with no problems with interference and harmonics.  There are ICs that can help you implement this, I'll try to find some circuits and post them.  This technique is also called Zero-Crossing control, as you only switch the load on and off when the voltage / current crosses zero.