Hot water extraction
Hot water extraction is often called 'steam cleaning', although very little steam is involved. The carpet is first vacuumed and pre-treated with a cleaning solution that loosens oily soil. Then hot water (sometimes with a rinse agent) is sprayed into the pile under pressure and immediately extracted with powerful suction, carrying dirt and residue with it.
It's the method most carpet manufacturers recommend for deep cleaning, because it rinses dirt out rather than leaving it in the carpet. Truck-mounted machines, powered from a van outside, provide the most heat and suction; portable machines are used where vans can't park close, such as flats.
Low-moisture and encapsulation cleaning
Low-moisture methods use far less water. In encapsulation cleaning, a solution containing polymers is applied and worked into the carpet with a rotary or cylindrical brush machine. As it dries, the polymer surrounds dirt particles in brittle crystals that are vacuumed away. Bonnet cleaning uses a spinning pad to absorb surface soil.
These methods dry quickly – often under two hours – and are widely used in offices and hotels for regular interim cleaning. They're good at improving the appearance of traffic lanes but don't rinse out deep soil as thoroughly as extraction.
Dry compound cleaning
Dry compound (or dry powder) cleaning uses a slightly damp, absorbent powder that's brushed into the carpet by machine. It attracts dirt, then is vacuumed out. Drying time is minimal. It suits carpets that shouldn't be wet, such as some natural fibres, and areas that must be back in use immediately. Thorough vacuuming afterwards is essential to remove all the powder.
How they compare
A quick comparison of the three main approaches:
| Hot water extraction | Low-moisture / encapsulation | Dry compound | |
|---|---|---|---|
| Deep soil removal | Excellent | Good on surface soil | Moderate |
| Drying time | 2–6 hours typically | Under 2 hours | Almost none |
| Best for | Homes, heavily soiled carpets, end of tenancy | Offices, regular maintenance | Moisture-sensitive carpets, quick turnaround |
| Residue risk | Low if rinsed well | Low if vacuumed properly | Powder must be fully removed |
| Pet urine and odour | Good with specialist treatments | Limited | Limited |
General comparison. Results depend heavily on the operator's skill and equipment.
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Which method suits your carpet?
The carpet's fibre and use matter more than any general rule:
- Synthetic carpets (nylon, polypropylene, polyester) in homes: hot water extraction for a deep clean
- Wool and wool-rich carpets: hot water extraction with wool-safe products and careful temperature, or low-moisture
- Natural fibres such as sisal, jute and seagrass: dry compound or very low-moisture methods
- Office carpet tiles: low-moisture interim cleaning, with periodic extraction
- Heavily soiled or pet-affected carpets: hot water extraction with pre-treatment and odour treatment
Questions to ask a carpet cleaner
Ask which method they'll use and why, whether they pre-vacuum and pre-treat, how they deal with stains, what products they use on wool, and how long drying will take. A good carpet cleaner will explain the trade-offs rather than insisting one method is always best. Some carry both extraction and low-moisture equipment.
Be cautious of very cheap 'per room' offers that leave out pre-treatment or use weak equipment – carpets can end up over-wet and dirty again quickly. See how to compare cleaning quotes and carpet cleaning prices.
DIY machines vs professional extraction
Hired and home carpet washers work on the same principle as hot water extraction but with much less heat and suction. They can freshen carpets but often leave more water and detergent behind, which slows drying and can make carpets resoil faster. Our guide to cleaning carpets at home covers DIY machines in detail.
