CSLB C-20 HVAC ContractorVentilation and Air DistributionMedium
A newly renovated home has elevated indoor formaldehyde levels from off-gassing new cabinetry and flooring. Which strategy would most effectively reduce this indoor air quality concern?
- AIncrease the whole-house mechanical ventilation (outdoor air dilution) rate
- BInstall a UV-C light inside the return air duct
- CUpgrade the filter from MERV 8 to MERV 13
- DReduce duct leakage to improve system efficiency
Show answer & explanationAnswer & explanation
Correct answer: A. Increase the whole-house mechanical ventilation (outdoor air dilution) rate
Formaldehyde and other VOCs are gaseous pollutants that pass through standard particulate filters regardless of MERV rating; they are best controlled through source removal or increased outdoor air dilution ventilation, which reduces concentration by continually replacing indoor air with fresh outdoor air.
Why the other options are wrong
- B. UV-C lights are effective against biological growth (mold, bacteria) on coils, not gaseous VOC pollutants.
- C. MERV ratings measure particulate filtration efficiency and have no meaningful effect on gaseous VOC pollutants like formaldehyde.
- D. Reducing duct leakage improves energy efficiency but does not address indoor gaseous contaminant concentration.
VOC Dilution Ventilation
Gaseous indoor pollutants such as formaldehyde cannot be captured by particulate air filters; the most effective mitigation is increasing outdoor air ventilation to dilute contaminant concentrations.
- Filters (even high MERV) do not remove gases/VOCs
- Activated carbon media, not MERV filters, target gaseous pollutants
- Increased outdoor air ventilation is a primary dilution strategy per IAQ guidelines
Memory trick: 'Gases slip past filters — dilute them with fresh air.'