Low-E-2 , low-E-3 , and no-E glass for heating climate
I’m replacing a 60*37 double pane picture window that’s failed for the second time. The Marvin salesperson is telling me my choices are Low-e 2 or “for compliance with recent Title 24 requirements” Low-e 3. Marvin wants $980 for the 2 or a bit more for the 3.
Now I thought 2 and 3 referred to which glass surface the low-E coating was applied to, which has to do with climate. (See also https://www.greenbuildingadvisor.com/blogs/dept/musings/all-about-glazing-options ). And thus I’m confused by terminology. I see elsewhere 2 and 3 refer to how many layers of metal, but 3 makes no sense as one of those layers must be on the exposed glass surface.
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So, the question is, what terms should I use to order the best glass for this condition:
- A house with no air conditioning, and no need for it due (Berkeley CA)
- Northwest facing window getting almost no direct sun except near sunset.
- Picture window, where coatings other than perhaps anti-glare, are undesirable.
I’d rather have a nice clear picture window, than minimal energy savings. I’d rather have something durable, over the need to landfill the window for a fourth time.
Is there a online shop that will sell a high SHGC Low-E picture glass panel I can adapt to this window, bypassing Marvin?
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Replies
Bryce,
Each time you add another low-e coating to a surface of an IGU, you improve the R-value of the resulting window.
The glass surfaces of a double-pane IGU (insulated glazing unit) are numbered 1 through 4, with surface #1 being the exterior-facing surface of the exterior pane, surface #2 being the interior-facing surface of the exterior pane, surface #3 being the exterior-facing surface of the interior pane, and surface #4 being the interior-facing surface of the interior pane.
When a low-e coating is installed on surface #3 or surface #4, it can be either a so-called soft-coat low-e coating (also known as a sputtered coating) or a hard-coat low-e coating (also known as a pyrolytic coating). A soft-coat low-e coating is easily damaged.
For surface #4, only a hard-coat low-e (a pyrolitic coating) is possible. A hard-coat low-e coating is durable and survives touching and wiping.
A conventional low-e double-pane window has one low-e coating (on either surface #3 or surface #4).
A low-e 2 window has low-e coatings on two surfaces, chosen among surfaces #2, 3, or 4.
A low-e 3 window (for example, one with Cardinal LoE3-366) has low-e coatings on three surfaces (surface #2, #3, and #4).
Surface 4 coatings are a relatively new development. If you search GBA for "surface 4 coating" you will get links to earlier discussion of the topic.
Bryce,
Here are links to earlier discussions:
Surface 4 low-e... condensation issues?
Surface 4 low-e... condensation issues? Follow-up questions.
Can Cardinal LoE 180 be applied to both surface #2 and #3 of an IGU?
Comfort Problems Related to Radiation (Comments)
Rating Windows for Condensation Resistance (Comments)
Hello Martin~
In my country, surface 4 applied low e coating is not actually popularized.
Is it worth using a surface 4 low-e? instead of a three pane glass? Not in the theory but in an actual application. In the states, there are a quite numbers of references applied with surface 4 low-e?
Pyrolitic / hard coat low-E on surface #4 isn't a huge cost adder, and brings the performance of the glass pretty close to triple-pane performance. The condensation risk issue only comes up in MUCH colder climates than Berkeley.
Cardinal's LoE180 (surface #2) + i89 (surface #4) has fairly high solar gain, almost twice that of typical U0.32 single low-E units(!), and can raise the cooling load substantially if it's a large unshaded west facing window. (They have other low-E coatings for surface #2 to quell that gain, if needed.) The northwest facing aspect will help keep the gain bounded at sunset by the amount of heat reflected due to the oblique incident angle, but know that it'll be higher gain than the glass it's replacing. With argon fill that glass is in the ~U0.20 range, varying a bit depending on the inter-pane spacing. It comes in at least 2 thicknesses.
Before you commit to Marvin's quote, consider calling a glass shop and ask what they would charge. I paid less for my Alpen triple glazed 40x60 unit with special trim application and interior wood veneer.. It seems you are beyond any guarantee Marvin might have offered so using a local glazier might be much less costly. Even considering labor costs the quote seems high.
As Roger says above, Marvin's quote is quite high. Last fall i bought 3 IGUs at 70X38" for $18.04 / sqft - so about 1/3rd the cost of your quote (plus ~$20 for silicone glazing compound and spacer blocks). My existing window frames (which had single glazing before) limited my retrofit IGUs to a total thickness of 3/4", so these used 3/16" glass and a 3/8" spacer, with argon fill and SolarBan60 low-e. You take a small hit using a 3/8" spacer vs a 1/2" spacer, but that is what fit.
2nd point: when choosing a low-e coating, really pay attention to the specs and model your exact orientation. There is a trade-off between the Solar Gain coefficient and the window U-factor - so if you go with a coating with a high-solar-gain coefficient, the window U-factor will be slightly higher (i.e., worse) than coatings with lower-solar-gain coefficients.
-> My windows get less than 30 minutes of somewhat blocked sun in the early morning, the rest of the time they are fully shaded, so for these windows i went with solarban 60 - which has a low solar gain coefficient, but the lowest U-factor of the coatings i could choose from. If the windows were southern facing and got more sun, i would have gone with a coating with a higher Solar coefficient (but the trade off would be a higher U factor)
Installation isnt all that challenging. Finding someone who will place an order with and IGU manufacturer is a bit tough, but my homebuilder can order from SIGCO directly.