I am having a 4000 sq foot, open concept, two storey house with basement custom built in Toronto, Canada. Due to health issues and an oversized wood-burning fireplace, air flow and quality is a serious concern. The plan is to install a premium humidifier, air clearer, hrv, and 90% EFF carrier furnace. The furnace the builder normally installs is a carrier 58MSA120, which is a one-pipe system. My research indicates that a one-pipe system is inappropriate because it uses inside air, and that I should get a two-pipe system. The builder and the sub-contractor disagree. Any advice would be greatly appreciated.