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Community and Q&A

Solar Heat Gain: Marvin vs. Andersen Windows

MaineAmanda | Posted in General Questions on

I’m in Climate Zone 6A (Maine), building 734 sq ft with south-facing clerestory windows.

I’m down to Andersen A-Series or Marvin Elevate for the building, neither of which has high SHGC, and wondering about special glazing on just the south-facing clerestory windows for passive heating (I want it toasty!).

Any thoughts on what glazing to request for Andersen A-Series or Marvin Elevate for south-facing clerestory windows? Or what SHGC to shoot for?

The “standard” options so far are:
Marvin Elevate double-pane: SHGC 0.30; U-factor 0.27
Andersen A-Series double-pane: SHGC 0.26; U-factor 0.27

It looks like “standard” Andersen A-Series are Low E-4, whereas Marvin is Low E-2, and both have alternative glazing (for $). Is Low E-1 enough?

I understand that Low E-4 can create the coolest interior surface which could increase air circulation (don’t want). Moreover I want to take advantage of winter sun to heat the space. I’m okay with double-pane for the clerestory windows because people won’t be physically close to them…I prioritized triple-pane in window seats and a kitchen window where human bodies will be physically close.

A couple of other notes:
– The clerestory windows are 3×3 feet each and 3 of 5 clerestory will be awnings to let out summer heat.
– Heating is heat pump in each space + backup wood stove for outages + “booster” heat because this is a yoga space that I want to keep toasty.

Thank you! All advice welcome!

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  1. [email protected] | | #1

    Andersen's Low-E4 and Marvin's LowE-2 are the same coating, Cardinal's LoE2-272, which is a moderate solar gain coating.

    Edit - Heatlock is Andersen’s name for i89 surface 4 coating. Low-E4, as Andersen uses it, is not referring to i89 surface 4 coating, in any way, unless it’s specifically called Low-E4 with Heatlock.

    Both companies offer Cardinal's LoE-180 as an option. LoE-180 offers the best combination of high solar gain, maximum VT, and lowest U factor performance of any coating on the market.

    Here is a link to a very recent discussion about LoE-180 and other passive solar coating and performance options.

    Edit - I noticed that you did reply in the other thread after I responded here.

  2. Expert Member
    Akos | | #2

    Amanda, for my clerestory windows I went with clear plus hard coat low E glass on #3 (I can't remember which exact one but very lightly tinted).

    My advice is similar to the one in the thread Greg linked to. Don't worry about SHGC, get the windows with the lowest U factor your budget allows. There are too many days with minimal sun plus nights in the winter are long, on those days you loose more through the windows than you gain from the sun.

    The cold I was referring to is from radiation loss on clear cold nights, you feel the universe trying to suck the heat out of the house. I don't get that feeling from any of the triple panes in the rest of the house. During the day with any minimal sun there is heat gain through the windows, unless there is a big snow storm, it always feels quite comfortable.

  3. MaineAmanda | | #3

    Thank you both!

    Akos, I think your point about days with minimal sun is valid, and I need to consider heat loss on those days.

    I'm still a little stuck on these, now considering the "downdraft" potential that higher solar gain might bring...Not sure if I'm interpreting things correctly, but it sounds like LoE-180 may generate more convective currents than the standard LoE-270, all else equal.

    In a room with a peaked ceiling like that - Maybe 13' at peak where the windows are vs. 8' on the other side - Can you see any value in windows that may produce greater air flow? For example could that help unstick the warm air that gets trapped up there?

    Thank you!

    1. Expert Member
      Akos | | #4


      It is not necessarily about downdraft potential of a specific window coating but about chasing SHGC at the cost of U value. My place would have been just about as energy efficient, a bit less prone to overheating on very sunny winter days and a bit more comfortable on clear cold nights if I would have gone with the same triple panes everywhere instead of chasing the ~3% energy efficiency improvement from the double pane high SHGC units.

      I have an operable section in the clerestory windows which I open a fair bit during the shoulder season and occasionally in the winter after a very sunny day. This used to be accessed from a ladder, which was a pain. I recently moved the operable unit so it is by the staircase to the loft for easy access and find that I use it now even more. Great way to get extra airflow and a very quick way to air out the house.

      If you are putting an operable section, I would definitely plan for an easy way open and close it. Some operable skylights come in a landscape orientation and can be installed on a vertical surface. Not cheap, but you can order these with a convenient remote control.

  4. ThirtyWest | | #5

    This is not a flame reply. But I hate my Andersen's. Yes A series. I would rate them as functional garbage. Several leaks that they have had a hard time fixing and horrific customer service. Andersen will blame the install every time. I am in Maine too and wish I had gone with Marvin's. Oh, well. If you do happen to go with the Andersens and want a white window make sure you get the white that you want. there is more than one shade.

    1. Patrick_OSullivan | | #6

      Just as another anecdote, I have A series casement, awning, and fixed windows and haven't had any issues for the year they've been installed.

      1. ThirtyWest | | #7

        Glad you've had good luck with yours. Maybe they have fixed some of the issues. Mine are 4 years old. Just out of curiosity, do yours have the brown glob of glue on the outside frame where the window are put together?

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