I've had a number of slow cookers in the past and all seem to be roughly the same in this regard:
- The outside of the unit is red hot to the touch when they're on
- The crock pot inside the unit can actually move around. It has maybe 0.5cm of clearance on all sides from the heating enclosure.
They're not chef-grade (if such slow cookers exist), but they're not cheap (~£50).
Is there a reason for this? It's frequently said that this is an energy-efficient way of cooking food (amongst many other benefits) and I don't doubt that, but the two observations above seem wasteful in any case.
If the crock pot fit snugly into the unit then you could have more conduction rather than only convection heating, and surely the unit also could have heat better-directed inwards and reduce the amount lost on the outside of the unit? Once you've done that, you reduce the energy input from the unit to prevent overheating, and save more money. The closest I found was this but thermal expansion of the ceramic crock pot is way below the clearance given, easily evidenced by just moving the pot around after hours on the High setting.
I appreciate that this question is a mix of physics and food, but I imagine there is a practical reason for this because it seems like such an obvious flaw on the energy efficiency side, yet it's across the market - I'm surely missing another consideration.