Sounds to me like the duct work feeding the ceiling registers are not insulated and are chilled down sufficiently to condense water from the heated air. With my HP the temperature is too low to use an evaporator humidifier in the forced air, such as is common with gas and oil fired furnaces where the plenum temperatures run well over 100 degrees. But I understand you to say you have humidifiers in the heat pump air stream. Perhaps I misunderstand, and that may be all my fault, it is late and I opened this thread seeing no one had responded. I haven't given your post the careful reading needed I'm sure, but offer the above with the suggestion, by all means, lower you humidity setting.

You've probably never been in a home with properly sized ductwork. Don't feel bad, it's estimated that as much as 3/4 of the heating and cooling systems in the US are oversized. 2 stage and modulating furnaces are better, but I've lived in a home with both, and both can be very comfortable and the single stage equipment doesn't make it feel more dry that I can tell. BUt you are correct, multistage cna reduce the sense of dryness you might get with a less than ideal system. THe RH of hot air is lower than cooler air, but cool air can make things feel drafty. That's why radiant heat is popular. You essentially have very, very low air velocities and much of the heat energy is indirect infrared heat which make you feel warmer, similar to direct sunlight. Keep in mind too, that unless you have an outdoor rest control for hte boiler or to sped up or slow the circulator, most hydronic air handlers are single stage for heating. So the heat is no different than a furnace. Worse, as you reduce BTU's to the coil, the airflow speed is usually ocnstant, so air temps get cooler. My point being, that a properly designed and installed furnace won;t make it feel dry even if single stage. But yes, oversized furnaces and those with restricted airflow can. Vairble capacity will always make the system more comfortable, but it will cost more. Radiant heat overall is superior, but the installed cost is much, much higher. That's why it fell out of favor. Same reason drywall took over the market and plaster disapeared. ITs' primarily a matter of cost. It's also why stone and brick homes aren't built anymore and concrete homes are the minority.

I have managed to get this to work on my own pool and spa but it depends on daily run time. Having a slight overdraw or underdraw can be a problem if you are running 24/7. However, when I did this, it was only for 6 hours per day run time. Since the valves are in partial open for both suction and return, having a few inches of gain or loss per day in the spa is equalized during the period of time when the pump is off. With the pump off and a connected primed channel between the pool and spa, water will seek it's own level via siphoning and the water level in the spa and pool will equalize to the same level. As I said before, it requires some tweaking so you don't have too much under/over flow in the spa but you can get it to work. It works even better if you have a variable or low speed pump where you can run both on the lower speeds. But again, if you don't want to bother with this then just use the manual swap method.

One of 3 things. 1) The spa shell is leaking either at a crack or a fitting such as the edge of a drain or a jet. Not real likely but possible. Possible but not really likely. Would require emptying the spa and checking the edges for gaps and cracks. Finding them means verifying with either a dye pen syringe (had a 3" tube to reduce currents) or food coloring to check if the spacing are drawing in water. 2) Check valve flapper's gasket is out of shape or there is debris at the edge. Most likely. Empty the spa below the jets and remove the 8 screws so you can pry the top off and look. Use a #3 Phillips to keep from marring the screws. 3) The valve in front of the pump is leaking. Not likely since NeverLube valves tend to be pretty reliable. Requires lowering the spa to pool height and removing the 8 screws holding the top of the valve. I am assuming the equipment is above the water level and below (requires the pool and spa be plugged, drains too). I know the actuator is attached to the valve. Use a #3 Phillips to keep from marring the screws. Scott