sump-pump-outage-planner

Use when a sump pump fails or the power goes out in a wet-basement house — estimates hours-to-critical water level from pit geometry and inflow rate, ranks response options by cost per hour of protection (battery backup vs generator vs water-powered), sizes a backup pump to actual inflow, and gives the failure-mode diagnostic tree (float stuck vs check valve vs impeller) with an emergency bailing plan.

Overview

A sump pump is the one appliance whose failure is measured in hours to flooded basement. When the power cuts out or the pump dies at 2 AM, you're not troubleshooting an appliance — you're racing water with a bucket. The math is simple and almost nobody has done it: pit diameter and depth give gallons-per-inch of rise; your soil's inflow rate (rainy-season night = worst case) gives inches-per-hour; division gives your countdown clock. That clock decides everything: whether a $150 battery backup is enough, whether you need a generator, whether you can sleep through the outage or bail every 90 minutes.

scripts/sump_outage.py computes the clock from five numbers you can measure with a tape and a bucket-timer, ranks backup options by honest protection hours, sizes the backup pump to your actual inflow, and walks the failure-mode tree (stuck float, frozen discharge, worn impeller, tripped breaker, failed check valve) so a 2 AM no-pump event gets the right first move instead of a panicky pump replacement that was actually a 4-cent zip-tie float repair.

When to Use

• Power outage with rain in the forecast and a sump in the basement.
• Pump running but water rising (mechanical failure diagnosis).
• Pre-purchase planning: battery backup vs generator vs water-powered backup for YOUR inflow rate.
• After a flood: figuring out why it happened before buying anything.
• Wet-season prep: testing the backup before you need it.

Don't use for: sewage ejector pumps (health hazard rules, different pump class), new-construction drainage design (inflow from soil engineering), or finished-basement active flooding >2 inches — that's emergency extraction, call pros.

How It Works

1. Pit geometry. Gallons per vertical inch = π × (diameter/2)² × 1 in / 231 in³. An 18-inch pit holds ~1.1 gal/inch; a 24-inch ~1.96. Usable rise = distance from resting water level to the floor lip or inlet that floods first (whichever is lower).
2. Inflow measurement. No instruments needed: during normal pump cycling, time how long the pump is OFF between cycles — water rose from "off" to "on" level during that time. Gallons/off-period ÷ gal-per-inch → inflow rate. Rainy-night multiplier 2–4× applied as worst case.
3. The clock. Hours-to-critical = usable gallons ÷ worst-case inflow. Verdict bands: >12 h = plan calmly; 4–12 h = backup essential, generator or battery sized accordingly; <4 h = high-risk pit, dual pumps + alarm mandatory.
4. Backup options ranked. Battery backup (40–80 Ah deep-cycle + 12 V backup pump): 6–15 h typical at moderate inflow. Generator: unlimited fuel-limited runtime, runs the main ⅓–½ HP pump (8–10 A surge ×3). Water-powered (municipal pressure): unlimited without power but uses ~1 gal city water per 2 gal pumped and needs 40+ PSI — worthless on a well. The script ranks by your clock.
5. Sizing check. Backup pump rated gph must exceed worst-case inflow × 1.5 or you're only slowing the flood. Table of typical 12 V backup (1,000–2,500 gph at 10 ft head) vs main (3,000–4,500).
6. Failure tree. Pump silent → breaker/GFCI, float (lift by hand: runs = stuck float, ~$15 fix), then power. Pump runs but water rises → check valve (short-cycling siphon), impeller worn, discharge frozen/blocked, air lock. Pump runs constantly → stuck-on float or inflow beyond capacity (that's a drainage problem, not a pump problem).

Using the Script

bash

# 18in pit, 14in usable rise, pump off-period 8 min measured, rainy night
python3 scripts/sump_outage.py --pit-diameter 18 --usable-rise-in 14 \
  --off-minutes 8 --on-off-gap-in 6 --storm-mult 3

# size a battery backup for an 8h outage target
python3 scripts/sump_outage.py --pit-diameter 18 --usable-rise-in 14 \
  --off-minutes 5 --on-off-gap-in 6 --battery-ah 75 --target-hours 8

# failure triage quick card
python3 scripts/sump_outage.py --triage

Outputs: gallons per inch, measured and worst-case inflow (gph), hours to critical, risk verdict band, backup option ranking with protection hours for your battery size, pump sizing check, and the 2 AM triage card.

Common Pitfalls

1. Measuring inflow on a dry day. A 40-minute off-period in August says nothing about April. Measure in wet season or apply the storm multiplier honestly.
2. Sizing backup by the main pump's rating. A backup needs to exceed INFLOW, not match the main pump. 2× your worst inflow is the target.
3. Forgetting GFCI trips. Most sump outlets are GFCI; a nuisance trip looks exactly like a dead pump. The triage tree checks it first because it's free.
4. Battery backup never tested. Deep-cycle batteries die in 2–4 years; the backup that "worked when installed" fails silently. Quarterly: unplug main, confirm backup cycles, plug back.
5. Check valve confusion. A failed check valve short-cycles the pump (water falls back, refills pit) — looks like "pump runs constantly but level never drops." $20 part, not a pump.
6. Discharge line freeze or blockage. Pump runs, pipe's full of ice or a crushed end: water has nowhere to go. Winter: discharge must slope away and exit above grade with an air gap.
7. Water-powered backup on a well. It needs municipal pressure; on a well it's a paperweight and the well pump is out in the same outage.

Verification Checklist

• Pit diameter + usable rise measured (tape, 5 minutes).
• Off-period timed during normal cycling; storm multiplier applied.
• Hours-to-critical computed and written on the pit lid.
• Backup pump gph ≥ 2× worst-case inflow.
• Backup tested by unplugging the main (quarterly, calendar it).
• Alarm (water sensor at critical-minus-2-inches) installed and loud enough to wake you.
• Generator/battery option chosen BEFORE the next outage, not during.