We moved in a few months ago to a new construction home and had noticed very high humidity inside our house, sometimes about 70-80%. When moving in the builders explained to us about the fresh air ventilation system and so we first suspected this was part of the issue. Our home has this fresh air ventilation system installed and we first noticed it was set to "override" which meant it was constantly pulling in outside air and so we set it to "off" and noticed pretty quickly that the humidity became much lower in the range of 50-60% which is what we would expect. In experimenting we also then set the fresh air ventilation system to "on" and even with it set to "on" we noticed that the humidity would get too high over time since my understanding is that it pulls in outside air whenever the heating/cooling is running and a set amount of time per hour.
So, clearly the fresh air ventilation system was installed for a reason and it does not seem to make sense that the only way to have it be comfortable inside is to have it set to "off". I am definitely not an HVAC expert and in doing some research I saw that based on the documentation provided with our system it is a "Multi-Speed ECM" (Carrier model number 58SC0A/58SC1A) and what I understood from my brief research was that means that the fan speed is variable and the fan should run at a lower speed for a longer time in situations where the humidity is higher to remove more humidity. I have also seen some thermostats that specifically have settings to adjust for higher humidity and I assume they are doing this by controlling the fan speed? The thermostat that came with out house is this one and it does indicate the current indoor humidity on the display but as far as I can tell does not have any settings for actually adjusting anything to do with the humidity. This made me think that perhaps our thermostat could be part of the issue but I haven't been able to find a lot of information to support this idea.
Any suggestions/tips/ideas are appreciated!