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What to choose between Sun-Tek ISFG 2549 skylight or Kennedy 4622ISFG skylight for a tile roof?

vileparle_2 | Posted in General Questions on

Roofer was supposed to put Kennedy 4622 ISFG skylight but brought in Sun-Tek ISFG 2549. Is one way better than other or we will be fine with the either one of them?

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    You're going to have to look at the specifications to compare these skylights. Call up the manufacturer and ask a few questions.

    1. It looks like the Sun-Tek skylights are rated for high wind areas. Is that what you want or need?

    2. Assuming that both skylights are made of glass, not plastic -- and it looks like they are -- then the two most important specifications are U-factor and solar-heat-gain coefficient (SHGC). You want both of these numbers to be as low as possible. If the Sun-Tek skylight has a higher U-factor and a higher SHGC than the Kennedy skylight, then you got an inferior product.

    -- Martin Holladay

  2. Expert Member
    Dana Dorsett | | #2

    It's not universally true that lower U & lower SGHC = better product when it comes to skylights. To know which one is going to result in lower annual energy consumption it's useful to simulate it in the context of your actual house, based on your sit'es location, skylight orientation, and shading factors. (In my case when I looked into repacing the higher-U higher SGHC skylight that the house came with, simulations showed it lowered the peak cooling load slightly, but increased the total energy use due to the reduced shoulder season solar gain.

  3. GBA Editor
    Martin Holladay | | #3

    Dana,
    You're right. Here was my logic: The question concerns a tile roof, so it's probably a house in Florida, Arizona, or California.

    -- Martin Holladay

  4. Expert Member
    Dana Dorsett | | #4

    While that may be correct, it's not good to assume. I have relatives living in a tile roofed house in rain-soaked cloudy western WA in a location with 10 months of heating season (!), and know of a few tile roofed houses less than 5 minutes drive from my snowy central MA home too. Tile roofs are everywhere, even where they don't necessarily make the most sense from a climate perspective.

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