Hot water heaters are doing this. You can buy a hybrid hot water heater for around $1200 from your local hardware store. The crazy upside is it acts as an air-conditioner for your garage, and the heat exhaust is used to keep the tank of water warm. They're loud, but it pays for itself in a few years.
I'm also surprised other homebuilders/designers haven't connected the a/c condenser heat exhaust to a centralized location for hot water tanks. I've seen a few people on YouTube do it however for their heated pools.
My parents have two of these in the attic of their new house. I went up there over the summer and it was noticeably cooler than the garage where the access is. This is in the summer in Texas.
They also put their HVAC into the attic and the entire house is insulated with spray foam, so the attic only a few degrees warmer than the house below it.
I need to ask them what the energy bills were but I imagine they were low enough to prevent complaint.
I'm also surprised other homebuilders/designers haven't connected the a/c condenser heat exhaust to a centralized location for hot water tanks. I've seen a few people on YouTube do it however for their heated pools.