Intervention
HVAC systems
Also: air handling unit, mechanical ventilation system
Heating, ventilation and air-conditioning — the mechanical systems that condition and move air in buildings. Well designed and maintained, they deliver filtered outdoor air at a known rate; neglected, they recirculate stale air, harbour mould and become a pollutant source themselves.
Why it matters indoors
HVAC performance is the difference between a building that meets ventilation standards on paper and one that meets them in the room. Audits routinely find outdoor-air dampers closed to save energy, filters overdue, and rates far below design. Recirculation with high-grade filtration (MERV 13 or better) controls particles; only outdoor-air supply controls CO₂ and volatile compounds. Condensate trays and humid ductwork are recurrent mould sources.
What the studies report
| Linked to | Effect | Population | Study design | Source | Checked |
|---|---|---|---|---|---|
| Airborne bacteria | difference 40.05 (-55.52–-24.58) | — · hospital room | systematic review and meta-analysis of indoor bioaerosols in hospital rooms: culturable bacteria and fungi compared between rooms without a heating, ventilation and air conditioning system, rooms with a conventional system and rooms with an enhanced system, pooled with random-effects models and assessed with the Agency for Healthcare Research and Quality checklist | F-1407 Dai et al. A systematic review and meta-analysis of indoor bioaerosols … (2021) | machine |
| Carbon dioxide (CO₂) | mean 1117 | school students · classroom | monitoring of CO2, temperature and humidity in fifteen classrooms and locations of the ADNOC Schools in Abu Dhabi (5,090 students) before and after cleaning clogged air-conditioning filters and intake vents, with outdoor reference measurements | F-0401 Towards Healthy Levels of Carbon Dioxide in Schools of the N… (2021) | machine |
| Carbon dioxide (CO₂) | mean 1087 | schoolchildren · classroom | European school measurement campaign (SINPHONIE final report) | F-0040 SINPHONIE Schools Indoor Pollution and Health Observatory Ne… (2014) | machine |
| Carbon dioxide (CO₂) | — | students · classroom | continuous monitoring of Boston public school classrooms over a school year, 245 million measurements | F-0043 Ge Decision tools for schools using continuous indoor air quali… (2025) | machine |
Each row is one Finding — a sentence as printed in one study, recorded with its page in the Coridum Knowledge Base. Follow the Finding number for the exact wording and the citation. Checked says who verified the row: machine means every automatic check passed and the surrounding text was read; person means someone read the sentence in the document. Rows are re-checked by a person over time. The studies are curated in the Coridum Knowledge Base; the reading of them together is a Claim, shown separately.
How strong is the evidence
-
In classrooms, mechanical ventilation may lower indoor carbon dioxide: two independent measurement campaigns found lower concentrations where central mechanical ventilation was present than where it was not.
A Claim is Coridum reading the Findings together, not a quotation from one study — according to Coridum. The grade follows the study designs behind it: A is the strongest, D means a single study or a mechanism.
In the literature
- Gorlach et al. Indoor Air Quality and HVAC-Associated Microbiome: Predicted Antibiotic Resistance Functional Profiles in an Office Building—A Preliminary Study (2026). doi:10.3390/su18168236 CKB 1041
- Fast prediction for multi-parameters (concentration, temperature and humidity) of indoor environment towards the online control of HVAC system (2020). doi:10.1007/s12273-020-0709-z CKB 0866
- Spatiotemporal Mapping of Ultrafine Particle Fluxes in an Office HVAC System with a Diffusion Charger Sensor Array (2025). ACS EST Air. doi:10.1021/acsestair.4c00140 CKB 1136
Studies in the Coridum Knowledge Base in which this term is used. The definition follows standard usage in WHO, ISO and textbook sources; it is not quoted from these papers.
CKB = document number in the Coridum Knowledge Base, our curated library of peer-reviewed studies. Follow the DOI for the original paper.
Cite this page
Coridum Research. HVAC systems. Coridum Knowledge G-0088, 16 September 2026. https://coridum.com/k/G-0088/