Replacement windows, Low E or not?

[Jay Y.]

Hi all, 

I have a property built in 1980 with original windows that are definitely showing it's age.  I met with a window contractor (America's Best Choice) and the guy presented me the option of getting windows that meet Low E.  I'd like to get people's opinion here whether they think I should or not.  Tenant pays all utilities and I'm replace 15 windows.

Thanks!

[Jim Adrian]

Always go with low e coating on the #2 of glass.   Argon gas is optional as some say the gas leaks out over time.  In general never go cheap on windows as this is one thing in a home that seems to get replaces once in every 30-50 yrs.  You need a product that will last/perform. This is the biggest area where a house will lose/gain heat/cold pending the season and make your hvac system work harder.  I like double hung over single hung windows for cleaning reasons.  I like fiberglass over vinyl any day of the week.  Fiberglass is more stable than vinyl.  Look for thermally broken windows.

The other thing to look at is the glass performance.  This is more important than the window frame.  Look at  % of visible light (higher the more natural)  35% to 45% is a good target number.  Winter and Summer U-value (this is the inverse of the R-value of insulation), the lower the better. A good target is 0.26 to 0.32, lower the better.  Example 0.26 u-value is 3.8 R-value and we put R-15 in the walls typically.  Lastly the Shading Coefficient, target around 0.30, again lower the better.   That is Glass 101 for ya!  There are other values in glass but then it gets complicated.

The lower the glass numbers the more it will cost. But will reduce the utilities allowing the tenant to have money to pay rent.   I believe this is one area where you pay for what you get.

This link has more info on glass and is one of the largest glass mfrs.  Your local shop probably gets their glass from here.  http://www.viracon.com/page/insulating