Condensation Resistance Now a Critical Rating?
I have always been an advocate of using performance ratings to aid in selecting a good window. If you have spoken to more than one window sales rep, you probably know why. Misinformation, shady tactics, and high pressure are all too common in this industry, and third party certified ratings serve as a way to cut through the salesmanship and compare replacement windows objectively. Unfortunately for you the consumer, things just got more confusing in that area.
Enter Energy Star Version 6
Much like U-Factor and solar heat gain, condensation resistance is a rating certified by the NFRC. In the past, this rating has moved nearly linearly with U factor in most cases, as it generally improves as the thermal performance of a window improves.
Whether you are aware or not, there are some MAJOR changes taking place in this area, and it has to do with the new 2016 Energy Star requirements for the Northern Zone, which call for a .27 U-Factor. To clarify, this rating only applies to the Northern Zone.
Other zones still use ratings that are more easily achieved, and still effective for those areas. On the plus side, .27 is a darn good U-Factor for double pane glass, and for the most part, to this point, only good to excellent windows have achieved that rating. The problem of course, is that there are A LOT of middling to poor performing windows on the market that could not hit that number. That is of course without utilizing glass technology that has side effects.
The standby in this area is a heavy coat (or more than one) of low-e, often 366 glass or comparable. This results in a pretty dark window that cuts a bit too much solar gain for many homes in colder climates. The newest, and potentially more harmful option is a surface 4 low-e coating. This is a coating of low-e that is applied directly to the surface of glass that you can touch from the interior of your home. You might think that this would be cause for concern with scratching and durability, however, these concerns are largely unfounded. The larger issue is how this rating affects condensation resistance, particularly since the region of the country in question struggles with window condensation issues as is.
To very simply describe what low coatings do, they reflect heat. By placing this coating on the interior surface, you effectively keep that pane of glass and the airspace behind it from warming. Colder glass= MORE CONDENSATION when all other conditions are equal. The condensation rating drops precipitously, by nearly 10 points in many cases. Ratings in the upper 50’s and 60’s are dropping down into the 40’s in some products with the surface 4 low e coating. While there are ways to mitigate the amount of moisture in your home to compensate, many homes in the Northern region have enough of a challenge doing that without injecting this additional difficulty into the equation.
What is the Solution?
Well, there are a few things that you can do actually. One, buy a double pane window that achieves a .27 or better without this coating. Incidentally, if you combine this with a good air leakage rating under .05 or so, you can be assured of getting a pretty darn good window. Two, buy triple pane glass, which in the Northern region should be given strong consideration anyway. Three, forego buying an Energy Star rated window in favor of one that will actually be better suited to your needs and budget. Personally I’d opt for option one or two, however, option three is better than unknowingly installing windows that may end up looking like a shower door in your home. This issue is particularly important for wood interior windows, as interior condensation is one of the leading causes of damage that I see to wood windows installed in the last 30 years.
Location is Key
One final thing to clarify, is that both the Energy Star rating in question, as well as the gravity of condensation as an issue are fairly unique to the Northern Zone and colder climates. This coating is not inappropriate in other regions, and in fact, is excellent technology when applied correctly.
In addition, it should be noted that Energy Star HAS proposed an equivalent certification where a lesser U-Factor can still qualify provided that the difference is made up by a higher SHGC. Unfortunately, those trade-offs are still somewhat challenging to achieve, and nobody wants to advertise a less efficient U-Factor since that is the number one rating that consumers use to compare.
Ultimately, the moral of the story is buyer beware. Do your homework when making a purchase of this magnitude. On the plus side, you are HERE, so that’s a great start!
Brandon Erdmann is the owner of HomeSealed Exteriors in Milwaukee, WI. He’s a window installation expert, a supporter of this site and an all around great guy. If you’re in the Milwaukee area and you’re thinking about new windows you should give Brandon a ring. You’ll be glad you did.
We are unable to buy .27 Energy Star windows in Alaska. What is the next best option? And, why are we not able to buy them here in the Northern Region?
I would bet that you are able to get windows at least that efficient. I was just in Alaska, went to the Iditarod start downtown and the restart out on the lake in Willow. Had a fantastic time. Anyway, the windows in the house we stayed in seemed very efficient although it was rather warm then. I believe Alpine Windows has a distributor up your way and I bet they have windows that exceed those ratings.
Check out these good little guys. They were ready to run!
where can I purchase the double pane, sealed windows to replace the leaking windows? I don’t want to buy the entire casement nor do I want to replace the entire window unit, just the broken-sealed glass units (like your video at the summer cabin). Can’t seem to find a place to purchase.
I don’t know of any national chains that offer insulated glass units, but you can usually find a glass repair shop that will sell you sealed units. You can also look for places that offer custom shower enclosures as they typically do all kinds of glass projects. Hope that helps!
Bad idea. The new glass warranty is totally dependant on the frame it goes into. A compromised frame probably led to your fogging/seal failure and it will do the same to your new sealed glass (which is why a compromised frame voids the warranty on the new glass). Replacing only the glass is as senseless as replacing pistons & gaskets on a cracked engine block!
I don’t know if that’s necessary true. I replaced a seal failure in my house several years ago and it’s still looking great. It’s the most popular video on our YouTube channel. I agree that replacing the glass isn’t always the best move, but I don’t know that the frame caused the seal failure.
I have a new home in Denver area built in 2021. Engineered wood floors and vinyl double pane windows. Window manufacturer did not indicate condensation resistance on product, although U-value shown as 0.3(+/-) depending on size. Floor manufacturer recommends 30% humidity for warranty. My windows start to show condensation on inside surface at around 20% to 25% relative humidity in the Colorado winter below 10 degree F outside. We typically keep the house at around 72 degrees F.
What condensation resistance performance should I expect from my windows? Do I have an installation issue? Should I consider replacing my two-year-old window system?
Well, 0.30 is not a very good U-Factor, but that’s not surprising since most builders use cheaper new construction windows. A more efficient window would have a higher condensation resistance rating and would increase the humidity level at which you’d see condensation. But, I don’t know how critical that really is.
I don’t know that I necessarily go out and replace windows that are decent just to get the humidity from 20 or 25% to 30%. The floor manufacturer might suggest 30%, but I doubt it’s required for anything. If so, that might change the calculation. I would guess the flooring manufacturer says something like that more to cover themselves rather than because it’s really required for the floor to avoid problems.
You might start by asking them if there is some minimum humidity below which you’d lose any warranty or anything like that. If there’s not any actual requirement (different than a suggestion) then I don’t think I’d lose any sleep over it.