Having your carpets cleaned is a chore that usually falls into the same category as spring cleaning: not very fun to do, but necessary, and should occur with approximately the same level of frequency. Most carpet owners, however, will only have their carpets cleaned once every few years (and some not even that). Carpet cleaning is not merely cosmetic. Having your carpet cleaned will revitalize your carpet and increase its lifespan. For optimal performance and duration, manufacturers recommend having your carpet cleaned at minimum every 12 - 18 months, depending on the amount of traffic in your home. In fact, many warranties stipulate this -- be sure to carefully read your warranty information.
While this recommendation holds true for all types of carpet, it is especially true in the case of nylon carpeting. Nylon contains a hydrogen molecule in its makeup -- this is the primary source of nylon's resiliency. When the fibers have been flattened down due to foot traffic, cleaning reactivates the hydrogen molecule, causing the fibers to literally bounce back. The cleaning will actually revive the carpet and enhance performance.
Hot Water Extraction
The primary method of carpet cleaning recommended by carpet manufacturers is hot water extraction -- more commonly (though slightly imprecisely) known as steam cleaning. In the hot water extraction method, hot water is essentially sprayed on the carpet and then sucked back into the machine, along with any dirt that was in the carpet. There is usually a cleaning solution added into the water to assist in the removal of stains. Technically speaking, true steam cleaning does not spray water on the carpet, but rather heats the water and uses the resulting steam to clean the fibers. However, today it is widely accepted that the term steam cleaning actually refers to hot water extraction, the most common cleaning process.
Professional cleaners may use either a truck-mounted unit or a portable machine. The portable machine has obvious benefits, such as being able to be used in apartment and condo buildings in units that would otherwise be beyond the reach of a truck-mounted unit's hose. However, truck-mounted units are more powerful than portable units, and should be used whenever possible for maximum efficiency.
There is also a plethora of do-it-yourself steam cleaning machines available for either rent or purchase. If your household is prone to spills or accidents that are difficult to clean, a small steam cleaner may be a worthwhile purchase to have on hand to tackle the resulting stains. However, for more general cleaning of your entire carpet surface, I highly recommend having a professional come to do it. There are too many variables with DIY machines -- the temperature of the water, the amount of cleaner to add, the exact method of use -- that present opportunities for things to go wrong.
Generally, DIY machines tend not to heat the water to the same high temperature as professional machines, which could result in less effective cleaning. In addition, these machines are not as powerful, which means that they are not able to extract as much of the water (and therefore dirt) from the carpet. When properly done, carpet should be only slightly damp after it has been thoroughly cleaned -- wet carpet indicates that the machine was not powerful enough to do the job effectively. If your carpet is very wet after cleaning, use fans to speed up the drying, and be sure to stay off it until it is dry. Do not replace the furniture before the carpet is completely dry.
If you do prefer to purchase a machine and clean your carpets yourself, be sure to read these tips on finding the best steam cleaner.
If you are concerned about the cost of having a professional come to clean your carpets, consider having only the traffic areas cleaned. This means that your big pieces of furniture, like the sofa, bed, etc., are left in place, and the cleaner simply goes around them. Not only do you not see the carpet under these large pieces of furniture, but it is not exposed to the air, light, and traffic the way the rest of your carpet is, so it makes sense that it does not require cleaning as often. (Of course, if you frequently move your furniture around, it would probably be best to have the entire surface cleaned.) Having only the traffic areas done should result in a cost savings over cleaning the entire area.