Low-level free area

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BS 6644:2011 — gas-fired hot water boilers, 70 kW to 1.8 MW net. kW is net heat input.

Figures

Room type

Appliance type

Draught diverter

Only changes mechanical Table 7. Natural high/low rates are the same either way.

Total net heat input (kW)

All gas boilers in the room, net. Individual boilers ≤ 70 kW still count if the total is over 70 kW.

Air supply

How often it runs

Enclosure vents communicate with

Building air change rate

Heated-space volume (m³)

Used only for mechanical heated-space: 0.5 air changes per hour.

Result

Notes

Guidance only — not a substitute for the standard

Figures are from BS 6644:2011 clause 6.9 for gas-fired hot water boilers of 70 kW to 1.8 MW net. You must still apply the current published standard, manufacturer’s instructions, and competence. Other heat-emitting plant in the room needs extra ventilation.

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