Preventing Pipe Freezing by Flowing Water in South Carolina Homes

Quick Guide: Preventing Pipe Freezing in South Carolina Homes

Primary risk: Exposed or above-ground pipes
Low risk: Buried pipes (12 inches or deeper)
Common prevention method: Allowing a small, continuous water flow
Typical flow needed: Fractions of a gallon per hour
Key factors: Pipe material, insulation, air temperature, wind speed, exposed pipe length, and inlet water temperature
Best practice: Maintain flow for the entire freezing period and ensure outlets and drains remain open

Why Pipe Freezing Is a Concern in South Carolina Winters

Winters in South Carolina are not usually very severe. Most winter days see temperatures substantially above freezing, and when temperatures do drop, they seldom go below 20°F.

Occasionally, single-digit temperatures occur in South Carolina. One or two days of temperatures below freezing may also occur. These cold periods cause concern about freezing water pipes.

Which Water Pipes Are at Risk of Freezing in South Carolina

Understanding which pipes are most vulnerable helps homeowners focus protection efforts where they matter most.

Buried Water Pipes in South Carolina

There is little reason to be concerned about buried water pipes freezing in South Carolina. Most piping systems are buried 12 inches deep or more and will not freeze even during extended cold weather spells.

Frost Line Depth in South Carolina

The frost line depth for most of South Carolina is only a few inches; United Facilities Criteria UFC-3-310-01 (1) notes a frost penetration depth of 0 inches for four locations in South Carolina (Beaufort, Charleston, Columbia, Parris Island).

Other sources suggest a maximum frost depth of 4 inches in the state.

Piping systems buried 12 inches deep should never freeze in our state.

Why Above-Ground and Exposed Pipes Freeze First

Pipes located above ground, however, are a point of concern. The temperature of water in exposed piping can decrease rapidly during cold weather, leading to frozen or partially frozen pipes.

Most South Carolinians take care to insulate exposed or outdoor piping and faucets. This generally works well during mild freezing events (down to 20° F), and depending on the amount of insulation used, can work well even during colder events.

Piping inside structures and under homes is usually not insulated in South Carolina due to heat inadvertently provided by heating systems under the building or radiated into the crawl space from the floor above.

However, extended cold spells (two days or more) or single-digit temperatures may cause some pipes to freeze under homes, depending on pipe location (such as near an open crawlspace vent).

How Flowing Water Helps Prevent Pipe Freezing in South Carolina

One common method used to prevent pipes from freezing is to allow a very small flow of water to drip from a faucet continuously during a cold spell. This water movement allows a small amount of warmer water from the well or municipal water system to continuously enter the pipe, adding a bit of heat energy.

The question about this method has always been the same: How much water flow is enough to prevent freezing?

How Much Water Flow Is Enough to Prevent Pipe Freezing

The answer is, “It depends.” There is no single flow rate answer for every situation in South Carolina.

Consider the following factors:

• Pipe material
• Ambient temperature
• Wind speed (if any, depending on location)
• Exposed pipe length
• Amount of insulation on the pipe

The temperature of the water entering the pipe from the well or municipal water supply also has a large impact on the answer.

D. G. Stevenson presented a paper titled “Preventing exposed water pipes from freezing” (2) that provides equations and data necessary to determine water flow needs to prevent freezing in a variety of situations.

Tables of required flow rates for various situations can be generated from those equations for ease of use.

Water Inlet Temperature Assumptions for South Carolina

One of the requirements for the equations is the water temperature entering the pipe during flow. The United States Geological Survey (USGS) has a site titled “USGS Groundwater Historical Instantaneous Data for South Carolina” (3) that provides historical data on groundwater temperatures for decades.

The temperatures observed ranged from 20.8° to 21.3° C (69.4° to 70.3° F) for the sites measured on Hilton Head Island and Dafuskie Island on the South Carolina coast. Well water sources inland could reasonably be expected to be cooler.

Since no actual temperature data is available for inland (or mountain) well sites, an inlet temperature of 55° F was used for the calculations to err on the side of caution, realizing that many wells will have water cooler than the temperature measured on the coast.

Understanding the Flow Rate Tables

Tables 2 and 3 present two pipe sizes with different materials and ambient temperatures, providing a range of water flow rates to prevent freezing.

• Insulation values used: a thermal conductivity of 0.025 Btu/hr ft F
  (This is the ability of a substance to conduct heat. A smaller number indicates a better insulator.)
• Wind speed assumption: 5 mph
• Reason: Average South Carolina wind speeds are 2 to 3 mph; 5 mph errs on the side of caution

A pipe with no flow is also shown below each table, along with the time required for the pipe to fully freeze after the water in the pipe reaches 32° F. Wind speed has a large impact on these figures.

How to Measure a Small Faucet Flow Rate

Measuring water flow in sink 2 300 DPI.jpg
Bryan Smith, ©2026, Clemson Extension

The required flow rates provided are in gallons per hour (gph). One gallon per minute equals 60 gallons per hour. The flow rates provided are quite small. It does not take much water flow to prevent freezing.

The flow must be maintained for the entire time the temperature is below freezing; therefore, care must be taken to make sure that the faucet (especially an outside faucet) does not freeze at the outlet and block the flow, and that the drainage pipe or system does not close due to slowly freezing water continuously entering the drain and building an ice dam.

To measure a small water flow from your faucet:

1. Use a 3-ounce bathroom cup
2. Measure the time required to fill the cup with water
3. Compare to Table 1

Table 1. Faucet Flow Rate based on 3-ounce Cup Fill Times

How Much Water Is Used When Dripping Faucets to Prevent Pipe Freezing

One concern many have about this method is the amount of water used to prevent freezing. The flow rates are very low, so even if several faucets were left dripping for an extended period, the total water use would be minimal.

For example, consider a property with 4 faucets that need to be dripped to prevent freezing. If the faucets were allowed to drip for 10 hours and each faucet was set to flow 1 gallon per hour, the total amount of water used would be:

(4 faucets x 10 hours x 1 gallon per hour =) 40 gallons of water for the 10-hour period.

Normal household water use in South Carolina averages 120 to 150 gallons of water per day per person, so the amount used would be about one-third of that if another person “lived” in your home for a day (including laundry and showers).

If a well serves the property, the pump would turn on three times during the 10-hour period if no other water is used (typical “40-gallon” bladder tanks actually hold 13 gallons of water dispensed between pump turn-off and pump turn-on to maintain system pressure).

Adjusting Flow Rates for Different Pipe Lengths

The tables below provide flow rates based on a 20-foot section of exposed pipe. To find the necessary flow rate for a shorter (or longer) pipe section:

1. Divide the flow rate selected by 20
2. Multiply that number by the exposed pipe length in feet

For instance, if you have 8 feet of exposed 0.5-inch PVC pipe with 0.5-inch thick insulation, assuming a 5 mph wind and a 5° F temperature is predicted, use the corresponding flow rate for that situation (0.62 gph from Table 2), divide by 20, and multiply by 8:

For 8 feet of exposed, 0.5-inch PVC pipe with 0.5-inch thick insulation:

(0.62 gph / 20 ft) x 8 ft = 0.25 gph

Table 2. Flow Required to Prevent Freezing of 0.5-inch Pipe

Assumptions Used for Table 2:

• Water inlet temperature: 55° F
• Wind speed: 5 mph
• Exposed pipe length: 20 feet
• Insulation conductivity: 0.025 Btu/hr ft F
• Wind speed selected to err on the side of caution (average SC winds are 2–3 mph)

Time for pipe to freeze completely after water temperature reaches 32° F (no flow, 5 mph wind, 5° F ambient temperature, 0.5 inches insulation):

• PVC: 4.1 hours
• Galvanized Steel: 4.3 hours
• Copper: 2.9 hours

Table 3. Flow Required to Prevent Freezing of 0.75-inch Pipe

The following table provides the required flow rates to prevent freezing in a 0.75-inch pipe, under the same assumptions as in Table 2.

Time for pipe to freeze completely after water temperature reaches 32° F (no flow, 5 mph wind, 5° F ambient temperature, 0.5 inches insulation):

• PVC: 6.5 hours
• Galvanized Steel: 6.6 hours
• Copper: 5.0 hours

Special Considerations for Homes Using Private Wells to Prevent Pipe Freezing in South Carolina

Leaving water running to prevent pipes from freezing works well for both municipal and well systems. However, water does not flow in the piping between the well and the pressure tank unless the pump is running.

If the pump and pressure tank are in a well-insulated or heated building, this is not an issue.

However, if they are located in a poorly insulated location, such as under a decorative rock in the yard, the homeowner may want to allow enough water to flow to keep the pump turning on every few hours. This would help prevent pipe freezing between the pump and the pressure tank.

As previously noted, most 40-gallon pressure tanks hold 13 gallons of usable water; therefore, a flow rate of 6 gallons per hour may be useful in these situations.

Adding insulation and a safe heating system to the decorative rock would alleviate this need for water flow.