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I’m building a home in northern Virginia, climate zone 4

blueskye | Posted in Energy Efficiency and Durability on

I’m building a home in northern Virginia, climate zone 4. Most of the windows are to the open south, and we plan to shade them for solar access in winter and solar screening in summer. However, it’s not practical to shade some of the windows.

I plan to use high solar heat gain for the basement (and exposed concrete floor), and low solar heat gain for the second floor that will have enough heat anyway — and probably some mixture on the first floor with the master bedroom and living areas.

My question is: From both outside and inside, will low solar heat gain and high solar heat gain windows appear obviously different if they are (1) in the same plane and (2) adjacent? Thanks!

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  1. GBA Editor
    Martin Holladay | | #1

    There is no single answer to your question. Most observers can't tell the difference between these two types of glazing (high solar gain and low solar gain), even when the two types of glazing are in the same room.

    On the other hand, some people can tell the difference, because they have sharp eyes. Does it matter? That's hard to say. I suppose only you can answer the question.

  2. jackofalltrades777 | | #2

    Angle of the sun, exterior roof overhangs, room lighting, window curtains and shades, etc., all of these will play a role in how the light appears. What are the VLT or Visible Light Transmittance numbers on the windows?

  3. blueskye | | #3

    Thanks, Martin - and good points, Peter! I am interested in appearance both from inside and from outside.

    I'm not locked in yet, but it looks like we are going with Andersen Eagle windows with this range of performance:
    U-factor SHGC VT
    Low-E4 SmartSun 0.29 0.19 0.44
    Low-E4 (Standard) 0.30 0.29 0.49
    Low-E4 PassiveSun 0.30 0.47 0.53

    We may go for lower U-factors if there are still $ in the budget, but the VT still appears to be in this range.

  4. jackofalltrades777 | | #4


    Those VT #'s are very close and it would be almost impossible to tell the difference in the window visible light transmittance. The SHGC is how much solar heat gain comes into the home from the sun, not how much visible light comes in, that is what the VT# is about.

  5. blueskye | | #5

    Thank you, Peter -

    I also wonder if the LSHG windows would be a lot more mirror-like than the HSHG windows from the outside.

  6. jackofalltrades777 | | #6


    On the outside the lower SHGC windows will have some type of film on the window to reject the solar gain. This is factory applied and referred to as "Low-E" most of the time.

    So yes, I agree, the lower the SHGC the more likely it will have a mirror like finish on the outside to reject the solar gain.

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