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Negative house pressure, backdrafting, infiltration

What is going on

Possible causes and checks for: negative house pressure, backdrafting, infiltration.

Likely causes

  • Combustion/exhaust appliances taking indoor air
  • Exhaust fans
  • No make-up air

Check in this order

  1. Dedicated fresh-air duct with thermostat-interlocked fan
  2. HRV/ERV
  3. Keep house slightly positive

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Source: General HVAC service practice — verify per model. Written in our own words; check the manual for your exact model.

For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.