Airflow & ducts: General tips (part 2 of 2)

Short, practical technician tips on airflow & ducts for general. Check each one against the manual for your exact model before acting.

Smoke detector placement near ducts

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High-velocity air defeats detectors; exposed horizontal run → hang detector under duct just behind grille; concealed ducts → detector far from grilles; never in corners.

Steam humidifiers for heat pumps / cool supply air

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Evaporative and atomizing types need warm duct air; steam type makes its own heat.

Thermal precipitation

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Dirt streaks around warm-air grilles/windows come from room air hitting cool surfaces, not from the ducts; insulation/storm windows reduce it.

VRF doesn't do humidity or fresh air by itself

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Add ductwork/air handler/ERV.

Wet-bulb needs airflow & shade

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Rapid air over the wick; shield from radiant heat (up to 15% error).

Whole-house fan free cooling

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Cool evening + warm house: open windows, run attic/whole-house fan instead of AC.

Zoned systems need 400 cfm/ton

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Across the coil regardless of how many dampers are closed → bypass (barometric or motorized) damper between supply and return; optional freezestat, supply/return sensors, outdoor reset.