Me too at first but I guess its not because VE offers a dimming version of their VE200. From what I've been reading, it seems proportional is still an on/off but it pulses it faster when more heat is needed and slower when less heat is needed. Where as dimming works like a lamp dimmer by lowering or raising voltage as needed. Now I might be wrong but this is what I've gathered from reading up on the VE dimming model and my Herpstats.