warm air unit compartment ventilation

8 Oct 2003
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United Kingdom
Just wondering how everyone is now classifying the ventilation on these boilers?. Suppose I have a j & s in a cupboard ventilated to the adjacent room, the vents are 50% undersized with no vent to outside. Combustion air is fed in via a vent in the loft into the return air duct and sized correctly with vents in the loft to outside all ok. Corgi say that all open flued appliances with compartment ventilation less than 90% is at risk. How do you guys classify this?
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I've only come across a warm air units taking combustion air via the return air duct on slot fix installations.

I would imagine the compartment ventillation would be the same regardless of the air intake posistion. Anything less than 90% is now At Risk.

When using return air ventillation the duct position/damper/and size requirement are given in the manual. The warm air outlet on the plenum to the room where the warm air unit is located must also be fixed open (and not user adjustable).

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