For the low-E... well if you want you can get storm windows made with it. I have been cautioned though that in storms you have to be excruciatingly careful as finger smudges wont clean off the coating without some nasty solvent, whereas in an insulated unit they can put the coating on the inside to avoid that pitfall.
The other thing about old windows and storms... I think a lot of people are used to windows that are not properly weatherstripped and the crappy aluminum triple track storms from the 60s/70s (that I'm dealing with) that dont seal well. If you tighten up the window a lot of those issues with frosting go away. You can do that on the primary window very easily and cheaply ( a couple dollars/window) with v-vinyl weatherstrip and a good modern storm like the Harvey s can be rather cheap ($100-$150/window) and seal nearly airtight.
The replacement window marketing "save $$$$$$ 50% on your heating bill" is a slight of hand that relies on two faulty assumptions they know must people will never check.
- They compare a modern triple glazed, argon low-E (R2.5 or R3) window to an old single pane window with no weatherstrip and no storm (R-1 if you are lucky)
- The "50%" savings is a savings of heat lost through the windows only. If you look at a typical old house like mine, windows account for maybe 10 or 15% of the total heat loss of the house. So the real savings is 50% x 10% = 5% !!
Ask a window manufacturer to show you a lifetime cost comparison of a replacement unit vs a storm and prove the savings. I bet they cant, as most replacements will fail before they reach payback. An example:
Lets say a single pane window = R1, a single pane with "good" storm = R2, and triple pane fancy replacement = R3
In my house I have 14 windows that are double hung single pane with old triple tracks. Lets be generous and say they are only R1.5 as I know they dont seal perfectly, and lets also be generous and call the windows 15% of my heat loss. In round numbers lets call my yearly heating bill $1000 of natural gas (its less than that due to wood).
Example 1:
replace all my windows with real wood divided lite triple glazed units. What am I looking at? $500 per or more. So I'm invested at least $7000 into windows. That will cut my heat loss 50% through the windows so 50% x 15% = 7.5% reduction x $1000 = $75 a year saved.
payback period = $7000 / $75 =
93 years
And in reality, my payback period is actually never, because we all know these replacement windows wont last 93 years before seals fail or some plastic part of the track mechanism breaks that's out of production and cant be replaced.
Example 2:
replace all my storm windows with airtight Harvey tru channels to bring the windows up to R2. At an average of $125 per I'm invested $1750. That will cut my heat loss 25% through the windows so 25% x 15% = 3.75% reduction x $1000 = $37.50 a year saved.
payback period = $1750/37.50 =
46 years
Even this is not worth it financially in my lifetime, but I may do it to improve the looks of the windows and cut down on condensation and road noise.
Even if I heated with oil and my fuel costs doubles I'm still looking at paybacks of 47 years and 23 years. And the numbers are worse if I take a loan and finance the new windows. And this is only my direct cost, we are not considering the life-cycle cost including disposing my old windows.
Compare that to the blown in insulation job I did for under $1000 that will pay back in under 5 years!
Good reading on windows:
(broken link removed to http://www.oldhouseguy.com/windows.php)
http://mysite.verizon.net/vze7aq8e/sitebuildercontent/sitebuilderfiles/about_old_windows.pdf
http://mysite.verizon.net/vze7aq8e/homewindowrestorationwork/index.html
many many many more:
http://historichomeworks.com/forum/viewtopic.php?t=1600&sid=d3b02090df4d0f491fec373ed87d5090