New windows, argon, krypton

[Si 330]

Trying to get an idea of how much more these energy efficient windows are over a normal double glazed sealed unit.

[J500ANT]

I say you buy one, you get one free

http://www.youtube.com/watch?v=acfMKefzqEo

[Simpo Two]

Apparently, you'll need planning pemission, building regs, building control, a FENSA certificate, an EPA certificate, a GCSE certificate, your driving licence and birth certificate. And you have to send £20 to somewhere. Your home will be reposessed if you do not do all of these. All certificates must be renewed every year and inspected by a certified inspector (call out fee £200 + VAT)

Frankly mate I'd leave the windows as they are

[Mart-1]

initially better thermal performance, slightly, but over time the gas particles in the cavity migrate out through the seals (relative molecule size allows this)

so it's not worth paying too much premium for gas-filled units

you're better off spending the money on other low energy products around the house