There are many ways to clean a carpet. Some work better than others, depending on the condition of your carpet.

Hot Water Extraction

In the hot-water-extraction method (sometimes referred to as “steam cleaning”), hot liquid is sprayed under high pressure into carpet pile and immediately vacuumed back out along with suspended soils. The liquid usually is hot water containing a detergent, but may be just hot water if carpet contains a detergent residue from previous cleanings. Performed properly, this method can clean even heavily soiled carpets.

This type of cleaning can be performed with portable equipment or truck-mounted equipment. Truck-mounted equipment generally does a better job than is possible with portable equipment on heavily soiled carpets. The truck-mounted equipment allows the technician to heat water (either from the home’s water supply or truck-mounted tanks) to a high temperature, and spray and extract the cleaning solution at much higher pressures than possible with most portable equipment. The high pressure allows the process to penetrate relatively deeply into carpet pile.

Many of what seem to be truck-mounted units are simply portable units bolted to trucks, and they lack power. The most effective machines are powered by an engine in the truck, rather than the home’s electrical system.

Many companies that use hot-water-extraction machines enhance their effectiveness by spraying the carpet with a conditioner and then lightly agitating the carpet with brushes before cleaning. The conditioner acts as a degreasing agent, which helps remove dirt and grime, and also lubricates the carpet so that the hot-water-extraction wand doesn’t distort the pile.

Companies affiliated with the Chem-Dry brand use its cleaning method. For years, Chem-Dry used a modified bonnet method (see below), but most companies affiliated with it now use its hot-water-extraction method, which mixes in a carbonated solution that, in theory, requires less moisture to be effective.

Shampoo

Shampoos for carpets operate like laundry detergents. Some shampoos also contain chemicals to reduce odor, retard soiling, brighten colors, and speed drying. The shampoo is released onto the carpet through openings in a rotary brush. The rotary action converts the detergent into a foam and works it into the carpet. When the shampoo dries, it leaves dry particles that can be removed by a vacuum cleaner.

Unfortunately, many of the loosened dirt particles are never removed and simply work their way deeper into the pile. Using low-quality detergent, too much detergent, or overly concentrated detergent may cause a buildup of a sticky residue on carpet fibers. Repeated cleanings without proper extraction will overload the carpet with residues that may accelerate re-soiling.

Combined Shampoo and Hot Water Extraction

High-powered truck-mounted hot-water-extraction equipment usually cleans even heavily soiled carpet—especially when used after carpet has been treated with a conditioner—but this two-step method is rarely employed in residential work. The shampoo and hot-water-extraction process uses shampoo and rotary brushes to loosen dirt particles, followed by hot water extraction using water rather than a cleaning solution to remove the soil. Although some professional machines combine the shampoo and extraction methods, the two steps are usually separate, and therefore incur extra labor charges.

Foams

Foams are really just a form of shampoo. Professionals use machines that generate foam and agitate it on the carpet with brushes. Foams used mostly by homeowners are available in aerosol cans. Foams are applied in a thin layer, then rubbed in with a damp sponge. When dry, the residue is simply vacuumed away. The main advantage to do-it-yourself users is that foam contains very little moisture, making it unlikely to damage carpet by overwetting. But the low moisture content also means that not much soil is removed, so this method mostly results in only surface cleaning. Some foams are difficult to rinse out, even with multiple cleanings, and may interfere with later attempts to clean the carpet.

Bonnet

Originally designed for use on commercial carpeting, bonnet cleaning uses a round absorbent pad, or bonnet, attached to the bottom of a rotary floor machine. Detergent is sprayed onto the carpet; then the pad is rotated over the surface, removing soil that adheres to it. When one side of the pad is soiled, it is reversed; when both sides are soiled, the pad is rinsed.

The bonnet method shares many of the same limitations as shampooing—many loosened dirt particles are never removed and simply work their way deeper into the carpet pile; using low-quality detergent, too much detergent, or overly concentrated detergent may produce a build-up of sticky residue on carpet fibers. And since companies that use the bonnet method rarely utilize a rinse process, repeated cleanings can overload the carpet with residues that may accelerate re-soiling.

Absorbent Dry Compounds

Dry powdery compounds containing detergents or solvents can be sprinkled on carpet, worked into the pile by machine, then removed by a vacuum cleaner. The detergent or solvent dissolves the oily film on carpet fibers, freeing the soil to be vacuumed out along with the powder after about half an hour. Although usually less effective than other methods, dry compound cleaning has special applications.