Re: Water heater heat pump
The heat pump on the water heater works using the same principles as a heat pump used for home heating. Since they are able to extract heat from outside -- even when it's 40 degrees outside -- and heat air to above the ambient temperature inside the house, there's no reason a heat pump water heater can't do the same.
As for efficiency, that's a tough call, because even though it's cooling your house, the additional heat your furnace needs to produce really isn't wasted... that extra heat goes into heating the water. And since the heat pump cycle is typically more efficient than the electric resistance heat that's the other option on the water heater, your total energy bill may still be lower when you run it in heat pump mode. But I am not an expert in that, so your experience may be different.
Since mold can grow in the dust that collects on the condenser coils of the WH heat pump, I wouldn't use that water for human or animal consumption. However, it may be just fine for plants. The water is nearly mineral free (aside from anything that might wash out of the dust), so may be ideal for washing windows or other things that could be affected by the mineral content of tap water.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.