Double glazed units

[pcooper]

I am hoping to change some of my Double glazed units as they
have steamed up but how do I now what thickness they are. looking around the units in my house I can find what look like three different
thicknesses and what is the best way to measure the size I don't want to order one that is too big

 

[Brutal]

How old is the double glazing?

 

[JonB]

Take the offending panel out & measure it.

 

[big-all]

if its an opener and not to heavy get some help and take the whole lot in to your d/glazers

 

[conservatoryTV]

Open your window and measure the frame width (inside to outside). Then measure the distance from the inside of the glass to the inside of the frame. Then measure from the outside of the glass to the outside of the frame and take those two measurements away from the overall width to give you the sealed unit size.

It's not perfect and you need to be careful. The most likely sealed unit cavities are 4-12-4 (20mm overall), 4-16-4(24mm) or 4-20-4 (28mm).