Filling in cut out for vents in living room flooring

[baby_belling]

Hi I used to have back boiler fitted and have since got a combi so no fire in the living room. I am now decorating and have removed the once mandatory ventilation grills in the flooring adjacent to each side on the chimney breasts with an intention to close them. the only problem is that under the grills there is a cutout approx 3cm by 15cm in the flooring. I want to know if it is possible to fill these in with a type of filler without having to replace the floorboards as i am just carpeting over the flooring. (not a fan of laminate sorry)

 

[Burnerman]

I wouldn't want to fill that sort of area - the filler wouldn't go off for ages anyway.
Cut a timber slip to the required size, but slightly plane a taper on the edges of the slip so when you bash it home, it grips tight. Add some PVA glue first. Fill any small irregularities with polyfilla or similar.
John

 

[foxhole]

You will need to cut a timber to fit under the floorboards and screw in from each end , then infill with timber or once carpet is laid you may put your heel thru.