Make sure whatever company you use knows that they are doing.

The most expensive part of that style window is the glass and I would be far more inclined to replace the entirety of the unit rather than just the glass.

Many of these palladians have frame rot and are sagging. Be sure to check that prior to committing to the repair of that unit vs. full replacement.

By the time you figure in the costs to do the equipment set up (scaffolding), manufacture the glass, install the unit, etc.....I would have to imagine that the cost for the full window replacement is extremely close in price and possibly cheaper.

I can say for certainty as I have never seen one quoted out as just a glass replacement, but it can't be cheap. From a labor standpoint, it is probably more difficult to work with that window from a glass standpoint as compared to a full replacement.

I would inquire as to whether or not the glass will be tempered. In applications such as these (huge windows), most companies will temper the window for both strength and safety (imagine being under that window if it ever breaks...it could be lethal).

replacement ease and cost will also be determined by the type of material the unit is made from and whether or not the unit is sash or direct set but WoW is right on in that the logistics will probably cost more than the glass itself and depending on the material quality and age of the unit it may be not much more expensive to replace the entire unit.

If I can play the part of the contrarian "one more time"....(don't hold your breath).....How old is the window? Is the glass still under warranty? Is there any kind of a grill pattern? (if so, is it Simulated divided lite, grills between the glass, or a wood interior grill?) Or is it just clear glass. Depending on the exterior of your home (brick, siding, stucco?) glass replacement may be the cheaper way to go. And if your glass is still under warranty, you may be able to get the glass for free and only be responsible for the labor. With regard to the heating coefficient, depending on the the proximity of other windows, now would be a good time to make a change in the type of glass you have if you want to change the heating, cooling, insulating aspects of that window (of course, changing it would mean that warranty won't cover any upgrades). The variety of Lo E Glass types out there offer a lot of options in that regard. Do you know the brand of window you have? Is it a vinyl window, an aluminum clad exterior/wood interior, or even wood exterior and interior window?

First, thanks to everyone for weighing in. While I'm not totally lost, I appreciate your much needed help.
Windowshopper, my house is 23 years old. Don't know who made the windows. The original window is double pane with grids. Trim is wood. There are also 2 sidelights, but they haven't fogged. The house has aluminum siding.
I had the windows on the back of house replaced last fall. Made a huge difference. I plan to replace the frontside soon. The original windows are wood, double paned with grids. Love em, but they are very inefficient.
Hope this add'l information helps.

Here is a link that might be useful:

First, thanks to everyone for weighing in. While I'm not totally lost, I appreciate your much needed help.
Windowshopper, my house is 23 years old. Don't know who made the windows. The original window is double pane with grids. Trim is wood. There are also 2 sidelights, but they haven't fogged. The house has aluminum siding.
I had the windows on the back of house replaced last fall. Made a huge difference. I plan to replace the frontside soon. The original windows are wood, double paned with grids. Love em, but they are very inefficient.
Hope this add'l information helps.

Here is a link that might be useful:

Okay, looking at the picture on the link you sent and knowing that the flanker windows have no problems, and assuming that the grills are wood removable grills, here is the bottom line.

The bottom line is that IMHO replacing the glass only in the center unit is your cheapest option in the short run. The next cheapest option is to take this opportunity and replace all three pieces of glass (the center and the flankers) with a higher grade of Lo E glass (lo E 366 comes to mind) NOW while you have the contractor or glass company out there (the idea being to get the best bang for your labor buck now while you have to have work done anyway). The higher grade of Lo E will help with the heat gain (unfortunately in both Summer and Winter months...so consider carefully)as well as increasing insulating values. You need to also be aware that Lo E also tints the glass, and many times it really can be noticeable, particularly if it is near windows that have a different kind of lo E (or no lo E glass). The best scenario, if you are planning to replace the entire window in the near future anyway, is to live with the seal failure until you are ready to bite the bullet on the whole thing being replaced. If the window is still in good shape, then unless your Palladian window is up in the clouds, glass replacement is probably your best bet. Whatever you decide....I wish you luck.

I agree with windowshoppers advice, the labor in getting set up with scaffolding and interior protection will probably cost more than the glass and labor to change it so you definitely need to consider carefully