Most (not all) windows with low e have a greenish tint when you look at them from certian angles, an easy way to see it is to lower the top sash so you're looking through both sashes at the same time. If your windows were custom made alot of manufacturers put warranty stickers on the frame, most times they hide it above the top sash. If you can find one there will be the manufacture's name and a series of numbers. They can put that number in their computer and have all the specs of that window, from the sizes of the sashes, the contractor who ordered them, 1 lock or 2, and if they have low e glazing and argon gas.

here is a quick way to see if your
windows have a low e coating..
take a cigarette lighter & light it.
hold it up next to the glass.
if the flame is the same color @ the
lighter, the reflection in the first
pane of glass, and the second pane of
glass, it is clear glass.
if the flame is more yellow than orange on one of
the reflective panes, you have a low e tint.
(this was my test before the purchase of a light
meter to actually measure the amt of light entering)
cold climates should have a low e coating on
the outer of the inside pane
hot climates should have the low e coating on
the inside of the outer pane.
cold climate location is to reflect heat back into
the house, hot climate location to reflect heat
out of house.
some glass mfgs put window glass composition
on the glass on the lower corner..
hope this helps..

neat trick energy rater!

thanks fusion866!
It served me well for several years
before the light meter purchase.

What she (ERLA) said - great answer btw.

ERLA, have you ever used a laser IGU thickness measurement gauge? They are rather pricy, but an excellent tool if you need to know the IGU airspace and they will also identify the LowE coating and which lite has it.

No Oberon I haven't used that toy!

Tell me why the IGU airspace is something
that we need to know..

Easiest way to identify if it has Low-e, is if the silver trim inbetween the glass has a date stamp on it, if it's after 2002, then the windows will have low-e, as this is standard regulations now (UK). Also another way to determine low-e is look at a bathroom window with patterned glass, if the patterned glass is on the outside, then this has low-e as the coating needs to be on the inside pane which is smooth..Again (UK) Climate conditions