1968, 18-unit masonry building in Chicago: we tightened to 1.6 ACH50 and added R-12 exterior insulation, dropping EUI from about 78 to about 32 kBtu/sf-yr. Budget only covers either balanced HRVs or triple-glazed replacements this year — what’s been the bigger real-world win for comfort and energy in Climate Zone 5?
At 1.6 ACH50 in CZ5, I’d “go HRV first” — balanced ventilation will steady IAQ, humidity, and odors across units, and usually beats window swaps on $/comfort unless the existing glazing is truly awful. Quick check: what’s your mid‑winter indoor RH and are you getting sill condensation; if RH >35–40% or complaints are all perimeter‑chill, windows may jump the line. @OP think of HRVs as the building’s lungs — do you have a per‑unit plan or a central setup in mind?
HRVs were the bigger win for us in a 1970s brick 24‑unit in CZ5 — comfort complaints and winter RH swings dropped fast and gas use fell about 12%; we used small ducted per‑unit HRVs tied to bath/kitchen with a boost switch and kept the existing double panes. If you’ve got chronic condensation or street‑noise issues, target the worst window stack first; otherwise I’m with @taylor_k92 on balanced ventilation. Do you have a clean route for stale‑air runs without opening fire‑rated shafts?
I’m with @torres74 on HRVs, but here’s a quick tell from our 1967 brick 20‑unit: if closed‑door bedroom CO2 overnight is often >1200 ppm, running 15–20 cfm continuous with a bath‑light boost kept winter RH about 35–40% and killed odors fast. If your north/windward stack has frosty aluminum frames and draft complaints, do just that stack’s windows; otherwise HRV — do you have a clean riser path for the exhaust runs?