You walk into a property after a tenant has left and you know immediately there is a problem. The carpets have been cleaned, the surfaces are clear, and yet the smell is still there. Cigarette smoke embedded into every surface. Pet odour that no amount of air freshener will touch. Sometimes it is harder to name but impossible to ignore.
For landlords, this is one of the most frustrating situations at a tenancy changeover. You can see the property is clean, but you know a prospective tenant walking in for a viewing will form an instant impression based on what they smell. And that impression is difficult to recover from.
Standard cleaning addresses what is on the surface. The problem with smoke, pet, and other persistent odours is that they are not on the surface. They are in it.
Why Persistent Odours Are So Difficult to Remove
When a property has been occupied by a smoker, for example, the tobacco compounds do not simply sit in the air and disappear when the tenant leaves. Over time, smoke particles deposit themselves into carpets, soft furnishings, curtains, wallpaper, plaster, and even the ceiling voids above. These embedded compounds continue releasing odour-causing molecules into the air long after the source has gone.
The same is true of pet odours. The compounds from pet urine, dander, and general occupation are made up of volatile organic compounds, the same class of airborne molecules that cause musty smells in damp buildings. They travel deep into absorbent materials and keep releasing over time.
Cleaning products, surface sprays, and deodorisers work by either removing surface residue or masking the smell with a stronger scent. Neither approach destroys the embedded molecules that are the actual source of the odour. The smell returns once the masking product fades, which is why many landlords find themselves going round in circles.
What Ozone Treatment Actually Is
Ozone is a gas that occurs naturally in the atmosphere. It is what gives the clean, fresh smell in the air after a thunderstorm. For professional odour removal, ozone is generated at higher concentrations using a specialist machine and introduced into a sealed space.
Ozone consists of three oxygen atoms bonded together. It is highly reactive, which means it does not stay stable for long. When ozone molecules come into contact with odour-causing compounds in the air or embedded in surfaces, they break those compounds down through a process called oxidation. The odour-causing molecule is chemically altered and its smell is destroyed at source.
This is what makes ozone treatment meaningfully different from masking products. It does not cover the smell. It chemically eliminates the compounds responsible for it, including those that have penetrated into materials well beyond the reach of any cleaning product or surface spray.
Ozone treatment of this kind is standard practice in fire and flood restoration, used routinely by insurance companies and restoration contractors to remove smoke odour after fire damage. The same approach has been adopted by hotel chains, vehicle hire companies, and letting agents across Europe as a reliable method for resetting a space to odour-neutral before a new occupancy begins.
Why a Tenancy Changeover Is the Ideal Window
Professional ozone treatment requires the property to be completely vacant. People, pets, and plants must be out of the building during the process. This is a straightforward safety consideration: at the concentrations used for odour removal, ozone should not be breathed in, and the space must be thoroughly ventilated before anyone re-enters.
This is not a drawback for landlords. It is actually why tenancy changeover is the perfect moment to use it. The property is vacant, the previous tenant has left, and the clock is running on finding a new one. Ozone treatment can typically be completed within a day, including the necessary airing-out period afterwards. It adds minimal time to the changeover process and leaves no chemical residue.
The result is a property that smells genuinely neutral. Not freshened up, not masked with a plug-in diffuser, but actually reset. For viewings, that makes a real difference. Prospective tenants make quick, often unconscious judgements about a property based on how it smells the moment they walk through the door.
What the Process Looks Like in Practice
A professional ozone treatment visit typically starts with an assessment of the property and the nature of the odour problem. This helps determine the concentration and duration of treatment required, as a heavy smoker’s property over several years requires a different approach to a property with a general pet smell from a shorter tenancy.
The ozone generator is placed in the property, which is then sealed. Treatment runs for a set period depending on the size and condition of the space. Once the cycle is complete, the property is ventilated, and ozone levels are confirmed to have returned to normal background levels before the space is re-entered.
The process is clean, leaves no residue, and requires no preparation of surfaces or materials beyond ensuring the property is empty.
Getting the Most Out of It
Ozone treatment works best when the property has first been thoroughly cleaned. The reason is straightforward. Ozone destroys odour-causing molecules in the air and those absorbed into materials. If there is still significant physical residue on surfaces, such as nicotine deposits on walls or urine residue in carpets, those surfaces will continue to off-gas odour compounds after treatment.
A good clean first, then an ozone treatment, gives the best results. In cases of heavy contamination, a follow-up assessment after the first treatment can confirm whether a second cycle is needed.
For carpets, curtains, and soft furnishings that have absorbed years of smoke, replacement is sometimes the most practical answer regardless of what treatment approach is used. A specialist assessment beforehand can help landlords understand what is worth treating and what has reached the end of its useful life, saving money on treatment that will only partially work.
When Ozone Treatment Is Worth Considering
For landlords, the clearest use cases are properties where a tenant has smoked indoors, properties with significant pet occupation, and any changeover where the smell is noticeably affecting how the property presents. It is also worth considering for properties that have been empty for an extended period and have developed a stale, musty quality that makes viewings feel flat.
It is a cost-effective, practical solution that fits neatly into the changeover window and requires very little from the landlord beyond booking it in. For a property that is otherwise in good condition but let down by how it smells, it is often the single most impactful thing that can be done before the next tenant moves in.