I just developed that sensation also. I had a hip arthroscopy to fix a torn labrum in my hip 6 months ago, but then during the 3 months of crutches/cane/rehab developed a bulging disc in my lumbar spine. I had gained a bit of weight during all this and when the heat sensation started I became paranoid that my recent weight gain had led to Type II Diabetes (which is why Googling your symptoms may not always be a great idea). This was ruled out by my PCP, and when I went back to my physiatrist she said that the sensation, which had now also manifested in my knee, was almost definitely due to the bulging disc impinging on a nerve. Hope this helps.
It appears that the warmth feeling in my calf increases after meals. any reason?
It is unlikely, but you should also rule out a blood clot.
The warm sensation in the leg could be a transient symptom of nerve compression (neuropathy). The origin could be in the lumbar spine. You will also have to rule out vitamin deficiency.
Sometimes, it is as easy as changing the posture or altering certain exercises.