What causes a warming sensation on bottom of right foot?

Sometimes. This could be a nerve entrapment locally in the foot or even as high as the back. Sometimes this can come from a side effect of chemotherapy or systemic disease like diabetes...
Neuropathy... Neuropathy is defined as a problem with the nerves and this can include the sensory nerves that control the feet. This change in sensation can occur from something local like a compression of a nerve or along the nerve path from its root or from some systemic diseases, such as diabetes. If you are concerned, see a podiatrist.