Halloween cauldron dry ice (lb)
Estimate dry-ice pounds for a fogging cauldron from runtime hours and burn rate for Prince William County porch parties.
lb = hours × lb_per_hour × cauldrons (+ storage_shrink%)
When to use
Use this for witch-cauldron fog effects where dry ice + warm water create rolling fog during trick-or-treat peaks.
Typical porch cauldrons burn about 5–10 lb/hour for continuous fog; pulsed refills use less. Buy close to event time.
Hours you will actively fog, not cooler storage time.
5–10 lb/h common for continuous porch fog.
Separate pots each needing ice.
Overnight cooler loss before the party.
Worked example
Example defaults — 3 h × 7 lb/h × 1 cauldron = 21 lb active.
With 20% storage shrink: buy about 26 lb (round to store pack sizes).
Add 1–2 lb every 10–15 minutes rather than dumping the whole block at once.
Second example: one input changed
From the defaults (Active fog hours = 3; Lb per hour (per cauldron) = 7; Cauldron count = 1; Storage shrink % = 20), the calculator shows:
Active dry ice: 21.0 lb
Buy with storage shrink: 25.2 lb
Approx. 10 lb blocks: 3 (round to what your supplier sells)
Now raise Active fog hours from 3 to 5 and keep the other entries. The result becomes:
Active dry ice: 35.0 lb
Buy with storage shrink: 42.0 lb
Approx. 10 lb blocks: 5 (round to what your supplier sells)
Comparing the two runs tells you how sensitive the answer is to that one measurement. If a small change in it swings the result a lot, measure it twice.
Limits / assumptions
Units: hours and pounds.
Assumptions: warm water kept topped up; outdoor or well-ventilated use; pellets preferred over huge blocks.
Not a substitute: venue CO₂ ventilation engineering or dry-ice supplier safety sheets.
Dry ice is extremely cold (−109°F). Use gloves/tongs; never seal in airtight containers; never ingest; ventilate enclosed porches.
FAQ
Hot vs warm water?
Hotter water = thicker fog, faster ice use.
Fog machine instead?
Use Fog machine runtime / low-lying mix tools.
Where to buy in PWC?
Grocery/ice suppliers near event day — call ahead for Halloween weekend.
Kids near the cauldron?
Barrier the pot; fog is cool CO₂ — keep clear of crawl spaces.