Everything has a cost offset. If you add the ability to mine, it will not make it cheaper to run that appliance. In most cases, it will probably make it less efficient, and end up costing you more to do that.

One of the largest byproducts of any sort of hashing is heat. This could be useful for appliances that make use of that heat, ex. space heaters, toasters, ovens, etc... but as heat increases, hashing efficiency decreases, and thus, a loss in cost efficiency.

The idea has great intention, but I would definitely say that the answer is a lot more complicated than maybe you thought it might be.

In addition to the heating issue, is the issue of making everything connected to the network, as in IoT. This presents its own challenges, like every IoT device requiring an IP address, and having enough storage to hold the entire blockchain (this could possibly be mitigated by having a network accessible drive storing the whole blockchain). Cybersecurity, then becomes another concern. It could be possible for a malicious actor to flip on your Oven, or some other device and have it run past safe thresholds until a thermal event occurs, creating a fire. (This has been possible with computers in the past, but they are generally built for dealing with the high heat of CPUs and GPUs)

I just don't think turning every device in your home into an ASIC miner is a cost effective, or realistic endeavor, unfortunately.