If your friend really needs an ERV, the small amount of air leakage of the inlet/outlet ducts will be benefical. Most homes need very small amounts of supplemental fresh air during calm weather. More important is supplemental dehumidification when the wind blows or fresh ventilation is provided. Cloths drier/bathfans/kitchen hood all need make-up air function. My research shows fresh air from a ventilating dehumidifier is of more benefit to the home to avoid negative pressure in the home. The ventilating dehu also deals with the excessive moisture in the home during wet cool weather. The secret is to maintain <50%RH while providing minimum fresh air to purge indoor pollutants and facilitate the function of the clothes drier, bathfans, and kitchen hood. In a perfect world, you could have both ERV and whole house dehumidifier. If you can not afford both, get the ventilating whole house dehu to provide make-up air keep the home <50%RH.
Most do not understand the complexity of the problem.
Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
Use +Merv 10 air filter. -Don't forget the "Golden Rule"