The IAQ can control humidity by either overcooling or through the DHM terminals on the EIM. The DHM terminals can either control a dedicated dehumidifier or a VS blower in the air handler. Either way, the IAQ has to be correctly programed, and the EIM DHM terminals have to be wired to the the air handler or dehumidifier properly. No bets on any of that having been done correctly. My new system is living proof that it can be done wrong. This thread reminds me that I need to correct it now that summer is nearly upon us. Even if the EIM is wired to the VS air handler correctly, the installer still has to program the IAQ for the correct brand. Rheem, for example, is different that most of the other makes. I recommend that you defend yourself by making sure you have all the relevant documentation on hand. You need at least five documents. 1. The VisionPro IAQ Operating Manual 69-1815EFS-06 2. VisionPro IAQ Total Home Comfort System 68-0287-1 3. Honeywell VisionPro Installation Guide 69-1816EFS 4. Honeywell VisionPro Installation Guide EIM 69-1823EFS-1 5. The installation/wiring diagram for your air handler. The four Honeywell IAQ documents are all different manuals, although there is some overlap. They are all available on line as PDFs. You will need to do a thorough Google search to get them all. The suffixes following the last dash appears to be the revision number. I would leave that out of the search. If you have a hard copy of any manual that covers the installer setup, use that instead of a download. Not all the downloads are current. If they didn't leave you one, demand it. Failing that, compare your PDF version with the actual settings on your IAQ. If the PDF is missing a setting or two, you have the old version. Lastly, you really need to learn all the programming of the IAQ, not just the owner part, but the installer part, too. There are far too many HVAC "pros" out there that don't have a clue on how to set one of these up properly. It's not just the dehumidification that you need to understand, but the AUX heat lockout settings as well. If not done just right, the IAQ will happily keep a very even temperature in your house by running the aux heat when you don't need it. That's how mine was left by the installers. Luckily, I spotted it before I got an astronomical power bill.

I doubt this is an issue for fresh air. There is a limit to how much fresh air you can bring in and it is much lower than the output of the air handler (most likely). So you have to use some recirculated air. Second, if there is something in your basement air that you don't want to breathe, then you have a problem independent of the setup. I am guessing the basement is unfinished? Air intakes are at the air handler all the time - I have a new house that is set up that way. So don't worry about that aspect. When I finished my basement, I found that I can meet all of my HVAC needs by just having a return there. It circulates the air enough to regulate humidity. I suspect the basement will get a little cold in the winter and I can increase the airflow but in the summer, closing the vents made the area perfectly comfortable. Hey - if it makes you feel better, I have a newer house with an expensive zoned system and they had to install an extra return in my master because of door slamming. When I have one zone calling for stage 2, there is more airflow than is comfortable. I have been building work arounds for the last 3 years. What I can say is that my bills are extremely low and after the work arounds, it is near perfect.

Well unfortunately there is more to making this work than merely just turning off zones. Carrier knows this which is why you have what you have. It's designed for less technical problems on the dealer end. Zone systems are a labor killer and as such you get what you pay for and in some cases of proprietary systems such as these what you pay for is mostly cumbersome nonsense that really doesn't work. Because infinity system is mostly a communicating type technology I doubt you would be able to get a new zone system to work with the system. Carrier knows that as well. AFAIK, the upper tier of any manufacturing brand is going to have these kinds of stipulations. Which is unfortunate. Things appear to be changing with Goodman manufactured brands, but I think it's still to early yet for me to say much more than that. Bosch brand is another that alleviate the communicating aspect. These 'communicate' in an entirely different fashion outside the control of the thermostat. I service the Katy, Texas area.

Given that you're renovating I would say it's a good time to do it. It can raise the costs dramatically depending on a myriad of factors. If what you have is flex duct / going back with flex duct the costs shouldn't be too extreme, but this can lead to boot replacement and vent replacement so that can increase costs further than just duct work alone. You should replace with at least R8 flex duct if you are going back with flex. This can pose challenges because circumference wise these ducts will be larger than what you have now most likely. By using a minimum R8 insulated flex duct, this will increase the efficiency of the system, marginally in most cases depending on climate. It also wouldn't be a bad idea to possibly add an additional new filtered return at a known hot spot / cool spot within the structure. (hot or cool --dead air space that might be getting trapped, by adding a filtered return to this spot it will aid in the comfort factor of the structure.)