Coolant leak?
 

I recently bought my brother's 86 RX7. Its a GLX, has 65k miles, sat in a garage for 14 years (he moved to Hawaii, left the car here in WI). Today, I changed all the belts out, and added coolant, because the add coolant alarm was going off. After putting all the new belts in, I took her out for a little spin. As I reached 6500 rpms, I noticed a burning sensation on my foot. Hot coolant, coming in from the what I assume is the air vent, came steadily dripping in. Only at high RPMs though. Any idea what that might be from?

The heater core is likely bad, along with the entire cooling system if its been sitting for 14 years. The cooling system needs a THOROUGH flush, than fresh coolant put in it

Was this happening on the drivers side or the passenger side? There are 2 holes on the firewall that go to the heater core and ac.

I was afraid it was the core, but I was hoping it was maybe just a hose. It's only on the driver side

the easiest way to get the heater core out is by taking the dash out, at least to me, and at that point you can follow your feet burning leak back to its true point of failure.