1. Keep your heating and cooling system simple.
All you need for HVAC is a small gas furnace, a mid SEER a/c, and a whole house ventilating dehumidifier. In 10 years, when repairs are needed, they will be simple. This concept will allow you to maintain <55% relative humidity (RH) when the A/C is off and when the home is unoccupied with minimal electric usage.
2. Include fresh air ventilation to purge indoor pollutants and renew oxygen.
Provide 60-100 cfm (depending on the size of the house) of fresh air when occupied and to keep windows dry during cold weather.
3. Use a minimum of a MERV 11 air filter on the HVAC system to minimize allergens circulating throughout the house.
4. Keep the RH in your home <55% RH in the spring, summer and fall months.
This controls dust mites and mold along with keeping it very comfortable. Include an Ultra-Aire whole house dehumidifier for when the sensible cooling load is low and the outdoor dew points are +60^F. Dehumidifier will maintain 55% RH even with the a/c off. This reduces energy use significantly and makes the home healthy and comfortable.