Back Boiler Ventilation - Blocking ?

[KJR]

I have a gas back boiler in the chimney in the lounge. There is a "large" ventilator, approx. 15cm diam., in the front wall of the lounge which I assume provides ventilation for the back boiler. The problem with this ventilator is that it points in the direction of the the prevailing wind and, at this time of year, provides a chilly blast into the lounge.

What I would like to do is place a barrier, outside, about 15cm in front of the ventilator to stop the direct blast of air coming in.

Would this be OK?

TIA.

KJR.

[Ed Sirett]

The likely area of the vent will be at least 75 sq. cm. I suspect that modififying an approved vent for a gas appliance is strictly speaking off limits. However if the barrier is at least 5cm (my opinion) from the vent then I don't see that it will do any harm (or have that much effect).