It would be a good idea to take off the grates and check inside the air return vents and see how much trash the builder left in there. I was amazed at how much builders trash was left in our return vents.

Check under the air return area under the a/c-heat where the filter is placed. Again, ours was full of dirt/trash.

Cleaning ducts would have no effect on our air quality with that much trash/dirt in the return vents.

First, I don't think it has anything to do with the fact it's geothermal. I've lived in a home with geothermal for 11 years and homes with natural gas and electric previously. It is not any dirtier or cleaner.

Do you have an air cleaner on your unit? That can make a big difference. Do you change the filters regularly? It's important.

Do you have a whole house humidifier on the unit to use during cold months. The humidity levels could make a difference with the allergies.

rrah,

Agree with what you said
"First, I don't think it has anything to do with the fact it's geothermal. I've lived in a home with geothermal for 11 years and homes with natural gas and electric previously. It is not any dirtier or cleaner.
Do you have an air cleaner on your unit? That can make a big difference. Do you change the filters regularly? It's important.

Do you have a whole house humidifier on the unit to use during cold months. The humidity levels could make a difference with the allergies."

~ Air filters collects dust making it easier for us to clean and have a cleaner air to breath, for allergies and dry months it should be humidifier to keep the air moist and the other way around for cold season have a dehumidifier to help dry out your place