Off-Gassing: The Invisible Hazard in New Homes
A beautifully finished new home often conceals a hazard: chemicals volatilizing from construction materials and furniture. The main culprits:
Formaldehyde:
- Sources: MDF, plywood, adhesives, paint
- Dangerous level: > 0.1 ppm per WHO
- Peak off-gassing period: first 3-6 months
- Health effects: eye irritation, respiratory irritation, long-term cancer risk (IARC Class 1 carcinogen)
TVOC (Total Volatile Organic Compounds):
- Sources: wall paint, carpet, floor adhesives, new curtains, furniture
- Safe level: < 400 μg/m³ (WHO standard)
- Typical new-home levels: 1,000-5,000 μg/m³ in the first 3 months
PM2.5 from construction:
- Dust from cutting, drilling, and sanding
- Can persist in the home for several weeks
Off-Gas Timeline by Material
| Material | Peak off-gas | Duration |
|---|---|---|
| Oil paint | First 1-3 days | 1-2 weeks |
| Water-based paint | First 1-7 days | 3-4 weeks |
| MDF/Plywood | Months 1-2 | 3-6 months |
| Floor adhesive | Months 1-3 | 6-12 months |
| Carpet | Months 1-2 | 3-6 months |
| New furniture | Months 1-3 | 6-24 months |
New Home Ventilation Protocol: 4 Phases
Phase 1: Bake-Out (7-14 days before moving in) Run all air conditioners and fans simultaneously. Raise indoor temperature to 30-35°C for 8 hours per day to accelerate VOC vaporization. Then open windows and ERV to exhaust the released gases.
Phase 2: Aggressive Ventilation (months 1-3)
- Run ERV and exhaust fans 18-24 hours per day
- Check TVOC weekly
- If TVOC exceeds 500 μg/m³, continue ventilation — delay moving in
- Use HEPA H13 + activated carbon air purifier concurrently
Phase 3: Normal Ventilation (months 3-6)
- Reduce ventilation to 12-16 hours per day
- Continue monitoring TVOC and formaldehyde
- Targets: TVOC < 300 μg/m³, formaldehyde < 0.08 ppm
Phase 4: Maintenance Ventilation (after month 6)
- Standard ventilation schedule
- Monthly TVOC review
- Replace activated carbon filter every 3-6 months
TVOC Automation in Home Assistant
yaml
alias: "New Home VOC Ventilation Protocol"
trigger:
- platform: numeric_state
entity_id: sensor.living_room_tvoc
above: 400
action:
- service: fan.set_percentage
target:
entity_id: fan.whole_home_erv
data:
percentage: 100
- service: switch.turn_on
target:
entity_id: switch.all_exhaust_fans
- service: notify.mobile_app_owner
data:
title: "⚠️ TVOC High"
message: "TVOC: {{ states('sensor.living_room_tvoc') }} μg/m³ — Ventilation at maximum"
Recommended Sensors for New Homes
Formaldehyde sensors:
- Sensirion SFA30: 1,500-2,000 THB — high accuracy
- Winsen ZE08-CH2O: 800-1,200 THB — budget option
TVOC sensors:
- Sensirion SGP41: 1,200-1,500 THB (includes NOx)
- ams ENS160: 600-900 THB — good value
Recommended new-home sensor package:
- SCD41 (CO2) + SGP41 (TVOC/NOx) + SEN55 (PM2.5/PM10/RH/T)
- Total cost: ~5,000-7,000 THB
- Covers all critical IAQ indicators
