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How Sump Pumps Work

Choosing a Sump Pump
If your basement walls look like this, a sump pump might be a good idea.
If your basement walls look like this, a sump pump might be a good idea.
© iStockphoto/ Rob Broek

­Depending on the laws in your area, you may not need a sump pump. For example, if you've never had standing water in your basement and it's consistently warm and dry, a sump pump probably wouldn't do you much good. However, if the area under your house floods occasionally or feels damp and smells musty, there's a good chance y­ou have an issue with moisture entry. Along with other waterproofing steps, a sump pump would make your basement a healthier space and protect any possessions and appliances you store there.

One way you can check whether moisture is getting into your home through your basement floor or walls is by taping a 2-foot-square (61-centimeter-square) piece of plastic onto surface and leaving it in place for a day or two. If you're not sure where the moisture may be coming in, it's a good idea to do this in multiple spots. After a couple of days, check under the plastic -- if it's wet, you have a moisture problem.

The first step in dealing with basement moisture is to air it out and run a dehumidifier. Since most moisture that ends up in a basement comes from water draining around your foundation, check to see that your gutters and downspouts are in good repair and directing water at least 6 feet (1.8 meters) away from your foundation. In a couple of weeks, repeat your plastic sheet test -- if it shows moisture, a sump pump may be a good idea.

Since sump pumps have many options available, when choosing one, you need to make some decisions:

  • Manual or automatic: Although manually operated sump pumps are available and slightly less expensive, an automatic pump is far more convenient.
  • Horsepower: Sump pumps are commonly one-quarter to one-third horsepower. More powerful motors will pump more water, but you don't need to go overboard if your moisture problem is minor.
  • Head pressure: Head pressure is the height a pump can raise water. For example, a pump with head pressure of 12 feet (3.7 meters) can raise water to that height, minus about 10 percent for physical limitations like bends in pipes. The pump you choose must be able to lift water out of the sump pit and up to the outlet pipe.
  • Cord length: You n­eed to be able to plug a sump pump directly into a ground fault circuit interrupter (GFCI) outlet -- you shouldn't plug one into an extension cord.
  • Voltage: Most sump pumps for use in U.S. homes operate on standard 110-volt circuits. Pumps with 220 or 4690 volts are available but are more commonly used in industrial applications.
  • Backup and alarm systems: Choose the alarm notification and backup system that fits with your personal lifestyle.


Once you've figured out which pump you want, should you install it yourself or leave it to the pros? Find out how to choose on the next page.