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Calculate required drain pipe size
South Carolina receives 49 inches of annual rainfall. Storm drainage capacity is important.
Climate Zone
3
Electricity
$0.13/kWh
Labor Costs
85% avg
Determine proper drain pipe size based on fixture load
South Carolina is in Climate Zone 3 - Warm-Humid/Warm-Dry (moderate heating and cooling). Homes here typically have higher cooling demands than heating.
Proper drain sizing considers several factors:
A full bathroom (toilet, sink, tub/shower) typically needs a 3-inch branch drain minimum. The toilet alone requires 3 inches. The sink can be 1.5 inches, and the shower 2 inches. These branch drains connect to larger main drains.
DFUs are a standardized measure of drainage load. One DFU equals about one cubic foot of water per minute. A lavatory sink is 1 DFU, a shower is 2 DFUs, a toilet is 3-4 DFUs. Add them up to determine pipe size.
No. Plumbing codes require a minimum 3-inch drain for toilets. This is non-negotiable and exists to prevent clogs and ensure proper waste removal.
Horizontal drains rely on gravity. Too little slope and waste moves too slowly, allowing solids to settle and clog. Too much slope and liquid outruns solids, leaving them behind. The standard 1/4 inch per foot creates optimal flow velocity.