On straight heat, I have usually seen 86F+, although 87-90F is what I've used.
86F is the temp studies have found will kill ich using just heat, but I like to err a bit in case there is a cool spot in the tank or the thermostat is off. Add aearation and watch the fish behavior as oxygen levels will go down. If you see lots of gill movement or it staying at the surface it may not be handling the temps well or the aeration is inadequate.
Do not add medicines at that temperature level as it may be too much for the fish.