Dear Jeff

I live in Alaska and am going to replace the windows in my home with Low E Argon gas filled glass. I am getting different advice as to which side of the glass should be on the outside.

Bob Yerger
Bob:

I am tempted to give you a smart answer like they tell the guys installing sod on new lawns – put the green side up!. You put the outside side of any window facing the outside! Unless you are just buying glass panels, all window frames are made with interior trim for looks and exterior trim to keep out rain and drafts, and this determines which side faces out.

You will find that Low-Emissivity glass (Low E) means there is a coating on the glass or by lowering the iron content in the glass itself that helps reduce thermal heat transfer by increasing the “U” factor of the window. If this is done by a coating, it is usually applied to the interior glass and since it “reflects” thermal heat it makes no difference from which direction this heat is coming. In other words, it will reduce thermal heat passing through the glass from the outside to inside without reducing solar radiation passing through the glass, and it will reduce thermal heat on the inside from passing through to the outside which would be a heat loss.

I think you will find the Argon-gas filled space between the two layers of glass provides far more heat loss reduction and going with a larger “gap” will improve the energy performance over a “thinner” window assembly. Just for the record, they also make 3-layer thermal windows for very cold locations but remember that each layer you add will reduce the solar heat gain.

Hope this helps,

Jeff Yago

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