I was taught to apply Carb Heat when I reduce the RPM in my PA-28 to below 2000 rpm, so when I turn base and have reduced power to 1800 RPM that constitutes carb heat, if you dont reduce power to below 2000 rpm then I guess there is no need?
I would have thought that the more sensible option would be to apply it on final for the reasons Andy stated, there would be nothing worse than to screw up your approach and landing then needing full power if approaching stall etc only to find you have insufficient power due to carb icing, dont think this would go down well with the insurance companies
D.