Broan claims that the HEPA filtration on its new Energy Star–qualified heat recovery ventilators (HRVs) and energy recovery ventilators (ERVs) will remove 99.97% of airborne bacteria and viruses. HRVs transfer heat from warm to cold ventilation streams; ERVs also transfer moisture. A compact, 70 cfm model is available for small homes and a larger, 140 cfm unit for average homes. Prices range from $760 to $1,800. Broan, 800.558.1711, broan.com