Carnot had a lot to say about theoretical efficiency WRT input and output temps. For example if I did the math in my head correctly, the peak Carnot heat engin

Carnot had a lot to say about theoretical efficiency WRT input and output temps. For example if I did the math in my head correctly, the peak Carnot heat engine efficiency of an oven cooling down would be 30%, dropping to 0% as it hit room temp. Only way to boost the theoretical Carnot limit would be to boost the temp... sear more steak, bake less bread, etc. So if pessimistically it took a tenth of a kilowatt hour to heat up a kitchen oven, you'd get maybe a hundredth of a KWH out of a cooling engine (the rest goes to waste heat). Its going to be hard to environmentally amortize the cost of the heat engine. Spending the resources on better insulation would have a much higher payoff. Similar problem with the structure, you could collect energy off the hydraulic door closer, but it would be way better for the environment overall to dial up the weather stripping and door insulation than to gather a watt or two.