I asked this question with different goals in mind in January, and I was given a great solution to part of my needs: the Chilipad. Now that I have lived through both heating and cooling seasons, I have learned a lot about what I would like. I had the option to add some heating/cooling zones during my new construction, but decided that the cost would never be recouped, and I would just go with a single zone for my 1950 SF 2 floor house. Now that I have lived in it, and had a number of house guests, I am wondering if it is possible to add some zones and de/humidification as well as some sort of fresh air (ERV?). In the winter it is too dry, and whole house humidification would be a god send. Also, in the spring, and I suspect again in the fall there are periods where it is not too hot, but it is too humid, and the only way I have to deal with this is to cool my house with the A/C. I am very humidity sensitive. The dry in the winter is fine for me, but many guests find it irritating. The humid times of year though lead me to cooling th house too cool for many people's comfort. Any thoughts on adding whole house humidification/de-humidification? Also, the house is very tight. The word from the energy star audit and other paperwork I have says I need to run my bathroom fans 14 hours per day every day to get adequate fresh air into the house. This seems like a huge waste of electricity, plus I hate the noise of the fans. Would an ERV be a reasonable way to bring in fresh air? I am really bad about keeping these fans on, and the air quality in my house definitely suffers. And finally, I currently have a single zone. I have sized the heatpump to provide adequate BTUs to condition the basement, though no vents currently operate in the basement. I would like to add a separate zone for the basement when I add the ductwork and venting in the basement, and would like to re-zone the main house so that the upstairs and downstairs are 2 separate zones. I had the 2-zone option at build time, and ran out of money, plus didn't think it would save any money on conditioning the house. I think it could however make it more comfortable, and I regret not doing this. Dies anyone have any idea if doing this as a retrofit is going to be financially feasible? I am looking for a new HVAC company, as the people who installed my system have been very unreliable so far as far as support and service. Some details about the system: It is a 5-Ton ClimateMaster Genesis open loop system and forced air heating and cooling. Any advice on where I might start looking into this? Cost effectiveness of the solution is important, but not the only guiding factor. thanks for any help.

Everything you describe is theoretically possible to deploy and doing so may be anywhere from moderately to massively disruptive / expensive.

My guess is that you'll need some sort of active humidification in winter, though an ERV will help moderate the cost.

Whole house dehu (Thermastor, Aprilaire) are possible as well, but not cheap to install or operate.

So much depends on specifics of your system that internet assistance is limited

Since you have a 5 ton single stage adding zones would have to be very carefully designed in. I like the idea of the whole house dehumidifier, though again with a 5 ton 1 stage I'd like to know a lot about load first.
Do you have a heat gain load?
J