Halloween graveyard fog fan CFM
Estimate a gentle assist-fan CFM for chilling and drifting Halloween graveyard fog across a yard path — not HVAC room air changes — for Prince William County haunts.
assist_CFM ≈ (path_ft × width_ft × fog_layer_ft × refresh_per_min) × gentle_factor
When to use
Use this when a fog chiller or ground fog needs a tiny push along a tombstone path without blasting fog upward.
Haunt forums warn that high CFM fans ruin low-lying fog.
Start with a gentle factor of 0.15–0.35; many yard setups only need a 50 mm PC fan (~10–30 CFM), not a box fan.
Tombstone walk length you want fog to cover.
Width of the fog ribbon.
Target ankle-to-knee layer depth.
How often you want to replace the layer volume.
Lower = quieter drift; higher = more push.
Worked example
Example defaults — volume = 20 × 4 × 1 = 80 ft³; × 0.5 refresh = 40 CFM raw; × 0.25 gentle → ~10 CFM.
That is PC-fan territory — not a shop blower. Aim fog exit at ground level behind stones.
If wind is already moving fog, reduce the factor further or skip the fan.
Limits / assumptions
Units: feet and CFM.
Assumptions: outdoor open air; fan assists chilled fog; no duct static pressure model.
Not a substitute: manufacturer fogger CFM marketing numbers or HVAC sizing.
Keep fans and foggers dry and away from walkways. Never enclose heaters; follow fluid and electrical ratings.
FAQ
Why so low vs fogger CFM labels?
Machine output CFM is burst volume; assist fans should barely nudge cooled fog.
Dry ice instead?
Use Halloween cauldron dry ice (lb) for pounds; this tool is for air assist only.
Hose to a manifold?
See fog hose run length for duct length; still keep assist CFM low.
Box fan OK?
Usually too strong outdoors — fog lifts and clears.