The glass is held in by clips (for metal) or glazier points (for wood), the putty seals the glass only, it does not hold it in place.

I don't know how to post an image file here, but the first casement window on this website will give you some ideal of the metal window I'm talking about.
http://www.nps.gov/history/hps/tps/briefs/brief13.htm

I understand that there should be glazier point to hold the glass on the frame, but in my case, there were no glazier point or metal glazing bead used, and only the glazing or putting compound was used to seal and hold the glass. In fact after take off some of the old putting, I see the metal frame's grid muntins have holes for inserting clips to hold the glass. I believe only the vertical grid muntins have hole, which are above the top surface of the 0.5" low E insulated glass; the horizontal grids are less thick, and have no glazing holes.
Btw, I found a company provides this kind of service: replace the old single pane with double pane glass: Bi-glass in Boston, and I'm in California.

I had these metal casements in a house built in 1938, in NY. I saw no reason to maintain the "architectural integrety" of these units what so ever. Our weather might be a bit more harsh then in California and these windows were horrible. Frost on the inside, condensation would run down the metal and lay on the sill. Every year one or two panes would crack and have to be replaced. And yes, there were no mechanical fasteners to hold the glass in, only glazing putty.
I'm at a real loss why you would have spent any money on them. To retrofit high performance glass in a low performance frame make no economic sense.
Ron

Ron- Thank you for the advice about how bad a steel frame window is. But why companies still make new products and people still used them: http://www.torrancesteelwindow.com/gallery.asp

Yes, steel frame is less efficient than the new no character vinyl replacement window, but I don't see why it causes broken glass as you said. About condensation, maybe due to the old low efficient glasses caused the interior areas near the window becametoo cold, including the frame? What if with the low E IG glass installed, the areas will be much warmer, and there's no condensation.

Btw, the original frame doesn't have weather seals at all, and air leakage is the big problem for those old metal frame. I have looked at the new casement window, and I will buy and install the same seals on mine.

Sapote

Thank you for your advices, Oberon. I total agree that the saving from heating bill may not add up to the cost of the new low E glass, but I try to save the heating energy, and live in a more comfortable house. Also, I'm not in the process of choosing a new window; I try to improve my existing ones. Sure we know the steel frame is not efficient, but the frame only covers a small surface of the total window area. In this case, I still think most of the heat is lost through the single pane glass cells. Further more, using the low E IG will reduce the glare and solar heat into the house during summer. I don't think keeping the old 1/8" single pane glass is a wise choice, considering the labor required to re-glazing (putting) the glass cells. Yes, replacing them with Low E IG will cost money, but I think the new glass will save big in heating energy.
What about coating the metal frame with a sort of thermal insulating material?
I'm more concern about issues relate to installing the modern thicker IG into the 1930 frame.

Sapote

For those who is facing the the question of restore the old steel window or replace with replacement window, should read this artical:
The repair and thermal upgrading of historic steel windows
http://www.oldhouseweb.com/stories/Detailed/12281.shtml

For thermal efficiency, the article pointed out this fact:
"(3) One measure of energy efficiency is the U-value (the number of BTUs per hour transferred through a square foot of material). The lower the U-value, the better the performance. According to ASHRAE HANDBOOK 1977 Fundamentals, the U-value of historic rolled steel sash with single glazing is 1.3. Adding storm windows to the existing units or reglazing with 5/8" insulating glass produces a U-value of .69. These methods of weatherizing historic steel windows compare favorably with rolled steel replacement alternatives: with factory installed 1" insulating glass (.67 U-value); with added thermal break construction and factory finish coatings (.62 U-value)."

I think in addition to replace the single pane glass with low E IG, adding weather stripping will ensure to get the U factor less than 0.69, which cut the thermal loss to half.

Sapote

Hi sapote,

I also agree that restoring these windows is much better than replacing. They are architectually unique and should remain as part of the home.

In your environment, and based on your concerns about "reduce the glare and solar heat into the house during summer", you should be more concerned about Solar Heat Gain Coefficient or SHGC than about U-factor.

Note that in the article that you referenced they were talking about 5/8" or 1" insulating glass. How much space do you actually have for an IG unit? The thinner the airspace between the lites, the less effieicnt the IG unit.
But, as I said, you should not worry about U-factor so that is less of a concern.

The way to block direct solar heat thru your windows is by installing a LowE coating - as you have found from your research. But, not all LowE coatings are the same. You need a Low Solar Heat Gain or LSHG coating applied to the #2 surface of the IG.

The LowE coatings with the best perfomance numbers at blocking heat and glare are generally tinted coatings -
not tinted glass, that is a different material - but tinted LowE coatings.

But, if you don't want tinted windows (glass or coatings), then you will want to investigate the newest LSHG coatings on the market which have 3 layers of silver in the coating. One example is Cardinal's LoE366. I mention Cardinal's coating because it was the first of the triple-silver coatings on the market and it is the most likely coating that you will find for the residential market.

Again, U-factor is not the issue in your situation - although you will get some improvement by changing to and IG unit versus single pane, it won't be nearly as much as you might be expecting - SHGC is the more important issue with your situation. You can significantly improve your SHGC numbers by installing an IG with a LSHG LowE coating.

Would indoor storm windows help?

Hopefully they were able to do something with their windows after 10 years........

Your best bet is to start a new post with your question as opposed to hoping for help on a 10 year old post. Honestly there are very helpful people here who will be happy to help that will not be bothered with 10 yr old posts.