Hot Water Extraction (HWE) is a method of carpet cleaning. It involves a combination of hot water and cleaning agents being injected into the fibers of a carpet at high pressure and all lifted soil being removed by a powerful vacuum. Hot water extraction requires water hot enough to clean effectively and deeply but not hot enough that it converts to steam. There’s usually visible steam during hot water extraction cleaning, but it’s just very hot water and not pure steam. Carpet manufacturers usually recommend cleaning their products with hot water extraction for effective stain removal.
When hot water extraction — the most common and effective method — is used to clean your carpets, high-pressure tools are used to propel a mixture of cleaning agents and hot water into your carpet. Though commonly called “steam cleaning”, no actual steam is involved in the HWE cleaning process apart from steam that may escape incidentally from hot water. This process helps to loosen the grime, dirt, debris, and soil that can lurk, often unseen, in your carpets. When the cleaning solution comes in contact with the carpet, it is 50 to 120 degrees Celsius, depending on the heat available from the cleaning unit. In a modern truck-mounted carpet cleaning machine, water can be heated under pressure to over 150 degrees Celsius, but after passing through high-pressure steel braided hose and several manifolds, the water loses much of its heat.
Hot water extraction carpet cleaning is easy to understand. First, a powerful machine heats water in the cleaning truck. Trained carpet cleaning experts use a professional hot water extraction cleaning machine to inject water and a cleaning solution into the carpet and remove dirt. The machine then extracts the solution and the hot water back out of the carpet so that it can dry quickly. While there is visible steam from the hot water, it is the water doing the cleaning, not the steam.
During the hot water extraction method, professionals usually apply a cleaning solution first to loosen and break up the soil. HWE begins with preconditioning using a pre-spray cleaner with typical alkalinity of 7 pH or above being applied to the soiled surface, followed by light agitation with a grooming or pile brush. Then they spray hot water onto the carpet fibers and extract it immediately to flush the fibers clean and remove soil and stains. For heavily soiled areas a Counter-Rotating Brush (CRB) can be used after the appropriate dwell time. Next, the surface is passed over several times with a cleaning wand or rotary extractor to thoroughly rinse out the preconditioner, using an acidic solution to reduce the pH of the carpet fibers back to a neutral state. In the next stage, the carpet is dried using a fan or carpet dryer. The final stage is resetting the carpet pile to remove any unsightly wand lines, commonly referred to as “shark teeth”, with a carpet groom or brush. Hot water extraction is the better choice for cleaning, and this is the method used by most professional carpet cleaners, even those that refer to their cleaning as “steam cleaning.”