I'd like the experts here to weigh in on this. I've been hearing a lot of claims about the better IAQ you get with geothermal systems. In my mind, a forced air system is still a forced air system, so I'm not sure if there is any validity to that claim. But I'm not an expert. If you feel one way or another, please post, and substantiate your position with the facts. Thanks! I really look forward to everyone's response on this!
I cannot think of any reason why a ground source unit would provide any better IAQ than a conventional heat pump, with one exception. The ground source unit has no need to defrost. So there will be no reverse cycle cooling calls in the heating season. Consequently, the risk of "dirty sock syndrome" could be reduced. But the dirty sock microbe doesn't visit every household. So it seems a stretch to make much of an issue about it.
On the other hand, if you are comparing ground source with a gas or oil fired forced air furnace, there are considerable differences. One that is seldom talked about is the compounds that can emit from heat exchangers. Some chemically sensitive individuals will have difficulty with the cutting oils and other chemicals evaporating in the air through the ductwork. It seems about 25% of the population are disposed to have such reactions (based primarily on hereidty). Of course any time you have a fire in the cave, it increases the risk of gas or oil leaks and combustion byproducts. CO will get you regardless of your DNA.
With very long run times the GS heat pump can clean the air better with wet coil than most filters. I took an air advice particulate counter to compare dry coils VS wet coil and wet coil was = to merv 8. I hear that GS HP do not need yearly cleaning I disagree. the coil still get dirty, filter still need to get cleaned/replaced, parts still need to be replaced - motors relays get pitted, go down, stick, drag. I find most GS heat pumps still need 2 hr yr "tune up" " cleaning" I do not put gages on but will cheak amp draw, SP, temps, stat and operation. Back to better IAQ over all yes only with better air flow and better filter.