HTR1 revision notes
Fires and wall heaters — flueing, spillage testing and atmosphere-sensing safety.
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BS 5871: Hearth Sizing, Spillage & Atmosphere Sensing
- Gas fire and space-heater safety checksThe core safety checks for gas fires and heaters: flue and air supply, hearth and clearances, commissioning and user handover.
- Gas fire fuel beds, radiants and coalsWhy coals, radiants and fuel beds must match the maker's layout exactly, and how to judge the flame picture that results.
- Gas fire hearths and shielding: Approved Document JWhen a gas fire needs a hearth, how far the hearth extends, why its edges are marked, and how nearby combustible fabric is shielded.
- Oxygen depletion sensors (ODS) and atmosphere sensing on flueless gas firesHow a pilot ODS shuts off the gas as room oxygen falls, where one is required, and why it must never be bypassed.
Space-Heater Flueing and Spillage Testing
- Gas fire closure plate and catchment space checksChecks for the closure plate and debris catchment space behind an inset gas fire, including the minimum catchment size.
- Gas fire flue sizes, liners and fluepipes: Approved Document JMinimum flue sizes for gas fires, fluepipe sizing and clearance, how a flexible liner is fitted, and when a debris collection space is needed.
- Spillage test for an open-flued gas fireThe order and conditions for flue-flow and spillage tests on an open-flued gas fire, and what a failed result means.
Heater Types, Hearths and Carbon Monoxide Risk
- DFE fires: air vents and approved flue combinationsWhen a decorative fuel effect fire needs a permanent air vent and how it is sized, and which appliance, flue box and flue combinations may be used.
- Flueless heaters and the atmosphere-sensing deviceWhere 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.
- Heater types and where carbon monoxide risk comes fromHow flue type and heat delivery differ between gas heaters, where carbon monoxide risk comes from, and the signs to act on.
Use the appliance type to organise HTR1 revision
Identify whether the scenario describes an open-flued, room-sealed or flueless heater. Then connect that design to its air supply, combustion-product route and safety controls. Do not transfer a rule from one heater type to another just because both appliances heat a room.
Study the HTR1 guide alongside flue flow and spillage testing. For a ventilation calculation, first establish which rule applies to the stated appliance and location; the open-flued ventilation calculator explains the limits of its room calculation.
In-depth guides for this module
Longer walkthroughs that sit alongside the revision notes.
HTR1 revision guide: gas fires, space heaters and their flues
HTR1 revolves around fire types, the chimney behind them and proving the room and flue can live safely with the appliance.
Flame supervision device explained: what an FSD does and how it fails
An FSD detects flame and controls the gas supply if flame is not established or is lost.
More Gas modules
Every module has its own revision notes and question bank.