[[ I duct in from the attic so the water heater’s heat pump intake takes in warm air to improve the water heater’s efficiency]]
Excellent idea! We have a “Whole House Exhaust fan” which draws air from outside I. Through the windows, and up into the attic, which ends up cooling off the attic, but that is just wasting the “free heat” which could be used to help heat, or keep hot the water heater water (not so much in winter, but certainly in summer). The fan is great on cooler nights, (but sounds like being on a runway with jets taking off in all directions lol) but when humidity strikes, it isn’t much use even if it is a little cooler than inside ai.r - we usually run a small room ac in the ,iving room only, at the very worst of the Humidity (heat we can take, but the humidity is miserable when temp is over say 85-90 degrees-or so)
We end up having to run a dehumidifier in the cellar because of so much water in the air- can’t afford to run one upstairs plus ac, but the ac does act to draw moisture out of living room which is where we spend the majority of time., but sure would be nice to dehumidify the whole house efficiently- again, the heat we don’t mind so much- if it’s dry, not an issue, but the humidity is murder on us now.
I tried a “swamp cooler” where a fan blows air over ice, which cools the air, but it doesn’t remove moisture unfortunately and doesn’t work all that great.
With the var speed heat pump I also have a variable speed air handler for the home. What that means is my home heat pump and air handler are almost always running, but in low speed. So during the warm half of the year when I duct the cold air by-product from the water heater to the floor of the closet the water heater is in, where there's a new air handler for my home HVAC. No matter what time of day the water heater runs to heat the water tank (and produce free cold air), the home HVAC is always running to take in that free cold air and distribute it through the house.