There’s money to be saved with selecting your high performance windows without significantly impacting energy performance.
With regards to energy, window design in Florida means keeping solar heat gain out High performance windows achieve this by applying a low emissivity coating (low-E) to the inner glass pane of a double pane system to reflect the sun’s rays back outdoors. This principle is rated with a value known as the solar heat gain coefficient (SHGC). The lower the SHGC the better the glass is at shading from direct rays of sunlight. The other thermal characteristic associated with windows is the insulating property of the glass, known as the U-value. ( It is of lesser importance in Florida because the energy loss associated with solar transmittance is a much greater factor). The lower U-value, the better insulating qualities of the glass.
When it comes to selecting the right SHGC for your project, there is no simple rule to guide you, but here’s my three recommendations aimed at putting the most money back into your pocket without seriously effecting the energy performance of the home:
- In Florida, you will need high performance glass on the east and west facing glass. Use windows with a low SHGC (0.25 or less).
- For south facing windows- if there’s no roof overhang directly above your windows – you will need the same high performance SHGC on south-facing windows (0.25 or less). With a typical roof overhang of 18” not more than 2 feet above the window, the low-e window SHGC for southern facing windows can be increased to 0.3 (Note: Because the angle of incident sun rays on the south-facing windows is always high in the sky, it doesn’t take mush southern facing overhang to block out much of the summer sun on that side.)
- Use double pane, lower grade low-e coating on the north side (SHGC of 0.33 or less). The north side does not see direct rays of sun light, so a premium low-e coating to the glass will have very little solar reflective performance. Go with the lower performing low-e coating.
Price comparing a typical 3050 high performance, energy star double hung, vinyl window (SHGC=.20) with a same size lower performing energy star window (SHGC=0.29) and find a savings of about $50-75. Multiply that savings by the number of windows facing north and it begins to add up.