Re: Re: Insulating old windows
That type of window, at this stage, is probably a rare beast! Worthy of retention.
You could investigate having the single glazed panes replaced with a very thin double glazing (but as thick as the steel frame will allow). There is a Scottish company that does double glazed units with gap down to between 3mm gap specifically for ‘heritage’ windows (google slimlite). This would help but may not do a huge amount for the overall thermal efficieny of the window as a whole, as the steel elements will still suck the heat out!
The other (probably better/cheaper) option is to look at a secondary glazing system internally.