Air Brick Size

[Steve Lowe]

Hi,

Got the plumber in today installing a gas fire and he says the air brick is too small.

The fire's specifications says it needs 144 cm2 of ventilation.

I fitted a Screwfix single brick air brick which measures 22.9 cm x

6.5 cm

I make that 148.85 cm2

The Screwfix book say's its freeflow is 6500 mm2 (yes mm2) which would make it 65 cm2 which is a massive difference

How is the difference between physical area and free flow calculated ?

Regards

Steve.

- Steve Lowe

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[John]

Surely it isn't entirely "hole".

[Steve Lowe]

No - but why is there such a difference between 65cm2 and 148.85cm2 allowing for the internal fins etc surely wouldn't make that much difference

- Steve Lowe

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[Ed Sirett]

The air brick is more brick than air.

[dennis]

Welcome to the world of aerodynamics.. after a bit of training you will be an expert in skin effects and other things that reduce airflow. You may even understand why things like zalman heat sinks are such a poor design from the point of view of cooling. ;-)

[Steve Lowe]

Ah the good old zalman heat sink !!! - does the water stay warmer longer ?

Anyway - have found a 215 x 130mm airbrick with a 148 cm2 freeflow that will do the job.

The fire manufacturers say that a 215 x 65mm airbrick is OK - if they put that in writing then that solves one problem but from a safety / correct use point of view not too good.

Cheers

- Steve Lowe

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[Chris J Dixon]

I remember having a problem at the natural gas changeover. They told me that there was insufficient boiler ventilation. The builders had actually put a suitable air brick into the back of the sink cabinet, then fitted the sink so that it oversailed the cabinet at the front by enough to give adequate free area. This arrangement was dismissed as "adventitious ventilation" and they insisted I add another air brick.

Chris