In our three years in our home, we've dealt with varying degrees of humidity, using various techniques. The end result is that nothing has changed.
Here's the deal: in the summer, our house is about as humid as it is outside, which I would assume is pretty common. When we run our window AC units (one of which has a dehum. feature), the humidity reduces. We also run a dehumidifier 24/7 in our basement during the summer. It's not an overly humid basement, but we pull about 45 pints a day. The problem, however, is in the cold months. Starting in October, our basement unit begins drawing less water, but we also begin to notice the humidity more on our ground floor and second floor. At this point, we take the dehumidifier to our second floor and run it pretty steadily to reduce what is around a 75-85% humidity.
We do not have a range hood, but have a handyman scheduled to come and install an externally-venting on in the next month. We also run a 50 CFM vent in our small bathroom. My plan was to upgrade to 100+ CFM, but the rafters in my Cape Cod won't allow for a housing that is larger than 5 inches deep, and all larger units also are larger in size.
In terms of big spending, we've replaced our old, creaky windows with new, custom fit windows and also had a new roof and ridge vent installed, figuring that humidity rises with hot air and should, theoretically, vent the same way. I've been told to get a whole-house dehumidifier, but we run our heat through cast iron radiators, not forced air and therefore have no ductwork.
We've run into two isolated incidents of mold-growth on the surface of painted walls and want to avoid more widespread issues long-term.
Aside from just running exhaust fans in the bathroom and kitchen when showering/cooking and running the dehumidifier 24/7, what else can be done? Who should I seek out to help? Is this the job of an HVAC specialist?