If you have misty windows this means the seals have failed, a double-glazed unit is made up of two pieces of glass a spacer bar and a butyl or polysulphide seal which is applied around the edges with a hot melt machine during the manufacturing process.
Misty windows are unsightly and have a cloudy appearance which is caused when minerals build up on the internal surfaces of the failed double glazed unit. The minerals build up over a period of time when the condensation inside double glazing units forms and dries out many times.
There are many companies that offer a repair service or sell repair kits. The way these services work is they drill a hole through your spacer bar and either blow warm air through the unit to remove the condensation or insert silica crystals which absorb moisture. They then seal up the hole they drilled and put the unit back in.
The problem with this approach is they are not fixing the overall issue which is a broken seal so over 12 months or so the moisture starts to build back up and the problem has returned. We use brand new units and offer a 5-year warranty on everything we replace.
If you have failed units then they are not performing as they should, failed units have a higher convection rate so therefore lose more heat and cost more money. There are lots of options when it comes to replacement units but it basically comes down to A, B or C energy efficiency.
Building regulations mean C rated windows are an absolute must but just by having B rated glazing the average home would save around £155 year. We replace all failed units like for like but we do offer units as an upgrade with A or B rated glass for all existing windows.