Where a flueless gas heater may be used, how big the room and vent must be, and why the oxygen depletion sensor is a backstop, not ventilation.
The room does the flue's job
A flueless heater has no flue, so all its products of combustion, including water vapour and carbon dioxide, go straight into the room. Ventilation has to dilute and remove them. The room must meet the particular heater’s size and ventilation requirements. Some fixed flueless fires are specified for secondary heating, while some portable LPG cabinet models can provide the main room heat. Follow the model’s instructions and turn a portable cabinet heater off before sleep or leaving the property.
Sizing check (a room that is not an internal space)
For a flueless gas space heater covered by the general Approved Document J room rule, check 0.045 kW net per cubic metre, then the permanent vent for input above 2.7 kW. This worked room is 6.0 m × 5.0 m × 2.5 m, has no door direct to outside and is not an internal space; the heater is rated 3.2 kW net.
- Room volume: 6.0 × 5.0 × 2.5 = 75 m³.
- Maximum rating: 75 × 0.045 = 3.375 kW, so 3.2 kW is within the limit.
- Input above 2.7 kW: 3.2 − 2.7 = 0.5 kW; 0.5 × 5,500 = 2,750 mm².
- Permanent vent: 10,000 + 2,750 = 12,750 mm², which is 127.5 cm².
- An openable window is needed as well.
For this room, keep the calculated permanent vent clear and provide controllable ventilation to outside. Approved Document J has a direct-to-outside-door exception to the permanent vent in this category. Its table also directs LPG space heaters conforming to BS EN 449 to BS 5440-2, so do not apply this worked figure to every portable cabinet heater; check that model’s instructions and the applicable guidance.
Room and use limits
A portable LPG cabinet heater must not be used in a bedroom or bathroom. Keep the room ventilated and within the maker’s size limits; switch it off before sleep or leaving home. Change its cylinder in a well-ventilated place away from ignition sources and hot surfaces.
A fixed flueless fire has different siting rules. Only a room-sealed gas appliance may be newly fitted in a bath or shower room. For a bedroom, first check the statutory heat-input and safety-control conditions, then the particular fire’s instructions: one model may qualify while another rules it out. Having an atmosphere-sensing device does not let you ignore the room, ventilation or model limits.
The atmosphere-sensing device
On a flueless heater the oxygen depletion sensor (ODS) is the principal automatic safeguard against falling room oxygen. It is a backstop, not a substitute for ventilation. Repeated shutdowns need investigation: inadequate air supply is one possibility, but a draught disturbing the pilot or an appliance fault can also extinguish it. Never bypass the device or keep resetting the heater; leave it out of use until the cause has been found and corrected. Do not use a heater whose safeguard is missing or not working. A room-sealed heater does not rely on an ODS to monitor room oxygen because its sound combustion circuit draws outside air. That does not remove the need to check its case and flue for leaks.
Warning signs
Excess condensation can accompany heavy flueless use and inadequate ventilation. Recurring headaches are a separate, urgent warning of possible CO exposure, though they do not tell you the cause. Get everyone outside into fresh air, obtain prompt medical advice and stop the suspect heater if safe. Stay outside until advised it is safe to return, and leave the heater off until its safety has been assessed. Severe symptoms need emergency medical help.