I live in a council house built around 1960's and in the kitchen there are two vents in the wall to the outside.These were originally what they called larder vents,with a new kitchen having been fitted these vents are now redundant but unfortunately they were never sealed.The result is we now get icy blasts of air filling the kitchen and costing a fortune to heat.Could someone please advise me to the best way to seal these old vents without chiselling the wallis there some type of sealant I could use? (The kitchen is now ventilated by an extract fan)