Question

Does anyone have experience with Earthwise vinyl windows? We're building on a budget and our builder suggests their triple-glazed product.

Asked by Lisa Carey-Moore
Baldwinsville, NY

We are in Syracuse, NY, and have a 2800 sq ft design with a mixture of fixed and operable windows planned. Earthwise triple glazing only comes in double hung. It's an NFRC-certified window with a U of .25. I can't find any information re: SHGC or Visible Transmittance. Any feedback on this product or a comparably priced product would be appreciated.

Answer

Florian Speier

Answered by Florian Speier

San Francisco, CA

Zeitgeist Sustainable Residential Design

January 13, 2011

Lisa,

I agree that finding performance data on windows is not always easy. There are two ways to obtain this information online.

  • One is from the manufacturer’s website, but you will typically need to click yourself into the “architects” section of the website to get the full performance reports.
  • The second source of performance data is the National Fenestration Rating Council's (NFRC) website

Manufacturer's website.  In the case of Earthwise, you can get their performance data here for new construction.

But clicking on the testing report reveals that Earthwise has submitted your windows for testing with a myriad of glazing products, so we would need the exact model number and glazing variant to get a good answer.

NFRC.  An alternative way of searching is directly on the National Fenestration Rating Council (NFRC) website, but again we would need the model number for a precise answer.

The NFRC website provides simple-to-read results tables like the one here, which may be the Earthwise product you're considering.

Using SHGC and light transmission data 

Checking the NFRC data for Earthwise products, we can match for a window with a U-value of 0.25 BTU/hr/sqft as you mentioned, the products seem to have:

  • SHGC (solar heat gain coefficient) of 0.26 and
  • visible light transmission of about 0.46.

I have written a number of articles on the subject of U-value and SHGC on GreenHomeGuide.com if you want to read more in-depth about optimal values for these.  Check my Q&As for details:

In a nutshell, I am a strong proponent of getting a window with a U-value as low as possible, since this is beneficial in any climatic condition, but retaining an SHGC as high as possible to maximize solar gain in winter.

Limiting potential overheating in summer is much better controlled independently from the window, by something that can differentiate between summer and winter, such as shutters, overhangs or deciduous trees. If your project is new construction, you can incorporate any of these solutions.

Regarding vinyl

This being a green building website, I would like to mention that vinyl windows are not a green choice. It is a fairly toxic manufacturing process, and while many vinyl windows now claim to be recyclable, the fact is that it is difficult and hardly anyone does so.

In respect to their materials as well as their lifecycles, there is an interesting study published on the Chartered Institution of Building Services Engineers (CIBSE) website which you can read here. On the material PVC, which is what vinyl windows are made from, they have this to say:

“The production of PVC is also an energy-intensive process (70 MJ/kg) and produces many poisonous pollutants such as hydrocarbons, dioxins, vinyl chloride, phthalates and heavy metals required for processing...PVC decomposes very slowly and as a waste product it contains environmentally dangerous substances that can seep out into soil and groundwater.”

Additionally, their study finds that vinyl windows do not last as long as (well cared for) wood windows, and especially not as long as aluminum-clad wood windows (which require hardly any maintenance). I am well aware that wood and aluminum-clad windows are more expensive, but I would strongly suggest to at least consider them.

Other resources for windows

Regarding window selection in general, the magazine Fine Homebuilding recently published an excellent article about energy efficient windows in their September 2010 issue.

  • The article is not online, but your local library will have the copy available.
  • The basic findings of the article are that the best windows come from Europe, but they also found several American suppliers that get close in performance, although often by sacrificing the SHGC.

Over the years I have grown partial to European windows, and have since turned my belief in these products into a business. For projects for my clients I always source European windows through my company www.breezepanel.com, and it always results in better windows that cost less than if we had bought them locally. One drawback is longer lead times, but with proper planning this is usually not a problem, especially in new construction.

If you are looking for truly energy efficient windows, the Fine Homebuilding article referenced above is a great start. It lists and discusses seven of the best North American window products as well as importers of European windows.


For more information:

For more on vinyl windows, read Elizabeth DiSalvo's Q&A "Is there one brand of vinyl windows that is more energy efficient and reliable?"

Tagged In: energy efficient window, solar gain

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