Note that the exact formulation of plastic makes a big difference in UV resistance. One PVC can fall apart (edit: after years of UV exposure) while another holds up well.

Posted By jonr on 02 Dec 2012 09:38 AM
Note that the exact formulation of plastic makes a big difference in UV resistance. One PVC can fall apart while another holds up well.

Then I assume you dont use PVC pipes for your plumbing runs since PVC falls apart. What do you use? Cast iron? Im currently standing in Home Depot and I see PVC being used for conduit, plumbing, sewer lines, etc.

Posted By Lbear on 02 Dec 2012 03:14 AM

1 - As far as the published air rating for the Marvin fiberglass windows, Marvin Ultrex rating is the bare code minimum at 0.30. ...snip... Why install leaky windows in the first place?

Just as I suspected, you have no information about leakage rates for Marvin windows, or any of the other brands that you label as "leaky." Building codes in the U.S. generally require windows to meet a minimum standard for leakage rates less than 0.3 cfm/sq ft @ 75 Pa (yes, there are units associated with that value), and most window manufacturers say that their leakage rates meet that standard, but they do not provide actual leakage rates, which may or may not be much lower than this value.

How leaky is the worst case of 0.3 cfm/sq ft? Assume a 40' x 50' (2000 sq ft) home with 8' ceilings and 18% of the wall area with windows. That would be 259 sq ft of windows. If they leaked at the maximum of the spec of 0.3 cfm/sq ft at 75 Pa, correct to 50 Pa assuming a linear relationship, and the overall window leakage at 50 Pa would be only 52 cfm. If we assume the 2000 sq ft house was recently built, we would expect the overall leakage rate would be 3 or 4 air changes per hour (ACH), or roughly 800 cfm to 1067 cfm. The window leakage would be 6.5% to 8.7% of the total leakage, not really too "leaky" as you have contended.

Now these windows would not be suitable for a PassivHaus, but many of us believe that a pretty good house (PGH) is a more practical solution than a PassivHaus, spending any extra money on generating our own power rather than trying to meet arbitrary PassivHaus goals.

2 - DP Ratings are more than a window simply experiencing a catastrophic "blowing out" in a hurricane or high-wind storm. DP Ratings show the entire quality and strength of a window. A higher DP value indicates a windows ability to withstand greater wind, water and structural loads. ...snip...Even without the rain, a simple 30MPH wind can cause a DP30 rated window to leak air, irregardless of its AI rating.

So while a DP30 rated window is rated that it will not fail structurally up to 110MPH winds. It is only rated for wind driven rain events up to 40MPH and that is not considering positive and negative pressures that are found throughout a homes wall area. That means it most likely will leak air and rain when the outside wind is at 30MPH or greater.

According to a post by oberon at http://ths.gardenweb.com/forums/load/windows/msg0809090610559.html, this is NOT true. In this post, oberon, who I think works in the industry and seems very knowledgeable about window testing, states (the bolding is mine):

Air, water, structural is a three part test that determines much about a window's overall performance. Air infiltration is the first phase, water penetration is next, and structural is the third part of the test.

Windows are tested for air infiltration simulating a 25mph wind or a 1.56PSF pressure load - air infiltration is treated separately from both water infiltration and structural and it is independent of the design pressure of the unit. Said again - the air infiltration rate in a window is not based on the design pressure rating of the unit.

Both water penetration and structural testing, on the other hand, are based on the window DP rating. Water infiltration is tested at 15% of the design pressure and structural is tested at 150% of DP rating.

What this means is that a window with a DP30 is tested for water infiltration at 4.5psf (15% of 30psf) while a window with a DP40 is tested at 6psf (15% of 40).

A window with a DP30 rating should be able to keep out rain when its driven by 42mph winds and a window with a DP40 should be able to keep out rain when driven by 49mph winds...so while water infiltration is DP related - and air infiltration is not - the nature of air and water infiltration is different.

The structural rating of a window is as much about the glass as it is about the frame and sash system. In order to get a higher DP rating the window manufacturer has to consider the thickness and possible heat-strengthening (or tempering) of the glass as well as the use of higher-end hardware and good quality sealants in the frame and sash system. But, interestingly, there is nothing in the structural rating that specifically requires that the unit be air-tight.

A window can leak air like a sieve and still achieve an excellent DP rating. Likewise a window that is sealed tightly can have a lower DP rating but excellent air infiltration numbers. Obviously there are also many units that have both excellent air infiltration numbers and a satisfactory DP rating (relating to both structural strength and water infiltration).

By the way, I did look at your video link and concluded that the fellow making the video was going to be unhappy with any windows he puts in since he was trying to maintain too high an indoor humidity for the outside temperature and the window frame temperature. A 45% relative humidity at 70 F corresponds to a partial pressure for water of 1.12 kPa. The window frame is obviously below freezing, and the vapor pressure of water at 32 F is 0.61 kPa. So he has simply set up a water vapor pump to carry water from room air and deposit it on the window frame.

Posted By Lbear on 02 Dec 2012 01:16 PM

Posted By jonr on 02 Dec 2012 09:38 AM
Note that the exact formulation of plastic makes a big difference in UV resistance. One PVC can fall apart while another holds up well.

Then I assume you dont use PVC pipes for your plumbing runs since PVC falls apart. What do you use? Cast iron? Im currently standing in Home Depot and I see PVC being used for conduit, plumbing, sewer lines, etc.

Next time you are at Home Depot, note that some of the PVC, usually gray in color, is marked as being suitable for use in the presence of UV. jonr's statement is certainly true. Some plastic trash bags are purposely made to degrade with UV exposure. I had a windsurfing board made of vinyl (or some type of plastic) that came apart after a year or two in the sun.

Posted By Lee Dodge on 02 Dec 2012 02:43 PM

Just as I suspected, you have no information about leakage rates for Marvin windows, or any of the other brands that you label as "leaky." Building codes in the U.S. generally require windows to meet a minimum standard for leakage rates less than 0.3 cfm/sq ft @ 75 Pa (yes, there are units associated with that value), and most window manufacturers say that their leakage rates meet that standard, but they do not provide actual leakage rates, which may or may not be much lower than this value.

How leaky is the worst case of 0.3 cfm/sq ft? Assume a 40' x 50' (2000 sq ft) home with 8' ceilings and 18% of the wall area with windows. That would be 259 sq ft of windows. If they leaked at the maximum of the spec of 0.3 cfm/sq ft at 75 Pa, correct to 50 Pa assuming a linear relationship, and the overall window leakage at 50 Pa would be only 52 cfm. If we assume the 2000 sq ft house was recently built, we would expect the overall leakage rate would be 3 or 4 air changes per hour (ACH), or roughly 800 cfm to 1067 cfm. The window leakage would be 6.5% to 8.7% of the total leakage, not really too "leaky" as you have contended.

Now these windows would not be suitable for a PassivHaus, but many of us believe that a pretty good house (PGH) is a more practical solution than a PassivHaus, spending any extra money on generating our own power rather than trying to meet arbitrary PassivHaus goals.

A window can leak air like a sieve and still achieve an excellent DP rating. Likewise a window that is sealed tightly can have a lower DP rating but excellent air infiltration numbers. Obviously there are also many units that have both excellent air infiltration numbers and a satisfactory DP rating (relating to both structural strength and water infiltration).

By the way, I did look at your video link and concluded that the fellow making the video was going to be unhappy with any windows he puts in since he was trying to maintain too high an indoor humidity for the outside temperature and the window frame temperature. A 45% relative humidity at 70 F corresponds to a partial pressure for water of 1.12 kPa. The window frame is obviously below freezing, and the vapor pressure of water at 32 F is 0.61 kPa. So he has simply set up a water vapor pump to carry water from room air and deposit it on the window frame.

I clearly stated that Marvin advertises their Ultrex windows Air Infiltration rate as 0.30 cfm or less. That is their official number as per Marvin.

Now let me get this straight, you are going on record making the statement that windows with air leakage rates of 0.30 cfm or in your example 6%-9% of the total air leakage (259 sqft windows - 2000 sqft home) is insignificant and a sound energy building practice. Wow, you developed a website that talks about energy efficiency and you dissect ever single avenue to get the home as tight and as energy efficient as possible. You now do a 180 and claim that having air tight windows is basically overrated and windows that leak air at 0.30 cfm are sound practice to developing an energy efficient home.

Regarding DB ratings, what I had stated does not contradict your source from the Garden Web.com blog. I stated in my post that AI is NOT related to DB ratings. They are measured/tested in different ways. The Marvin fiberglass gets poor AI ratings and poor DB ratings. So the bold quotes you used don't even apply because the window leaks air and achieves low DP ratings. A double whammy. I don't understand on how you believe a window that gets 0.30 cfm AI ratings and DB30 ratings is a better engineered window than a window that gets 0.03 cfm AI ratings and DB70 ratings.

Regarding humidity levels. Ideal winter levels would be below 40% but 45% should NOT be causing his window problems. In his video he explains that it is only the Marvin fiberglass windows that are having these problems & the problem began after he installed the windows in 2009. Also, if you do a search and read other forums, you will see that the Marvin Ultrex are having this similar problem. Most people are blaming the air leakage on the windows for the problem.

What happens when cold exterior air hits warm interior air?

Posted By Lee Dodge on 02 Dec 2012 05:48 PM

Next time you are at Home Depot, note that some of the PVC, usually gray in color, is marked as being suitable for use in the presence of UV. jonr's statement is certainly true. Some plastic trash bags are purposely made to degrade with UV exposure. I had a windsurfing board made of vinyl (or some type of plastic) that came apart after a year or two in the sun.

I understand the vinyl/PVC is not the most UV resistant material out there. At the same time one has to acknowledge that not all PVC is created the same. When comparing PVC windows, I am not considering U.S made PVC windows. They are not even on the same page as European and Canadian PVC windows. Look at the profile of a Euro/Canadian PVC window and compare that to a typical U.S. made PVC.

Regarding fiberglass, I agree that fiberglass windows are a very good choice. Although no U.S. made fiberglass window can compare to a Canadian made fiberglass window. They have been utilizing fiberglass windows for much longer and have better engineered fiberglass windows over what U.S manufacturers currently make. Maybe that will change one day in the future but for now one has to go and buy Canadian if they want the best fiberglass window.

If a manufacturer can make a fiberglass window that performs as well as Intus PVC: VT .70, SHGC .58, U-value .15, and a have a 0.03 cfm air leakage rate, DP70 rated, triple pane Guardian glazing. All while costing around $35 - $40 per square foot of window area, delivered. I will be a fiberglass man. If I had won the Powerball, I would buy the top of the line Canadian fiberglass windows but since money is not unlimited, I am sticking with Intus PVC since they are the best bang for buck out there.

Posted By Lbear on 02 Dec 2012 07:35 PM
I clearly stated that Marvin advertises their Ultrex windows Air Infiltration rate as 0.30 cfm or less.

What you actually said was, "As far as the published air rating for the Marvin fiberglass windows, Marvin Ultrex rating is the bare code minimum at 0.30." There is no mention of "or less." Big difference, and something that you need to acknowledge.

Now let me get this straight, you are going on record making the statement that windows with air leakage rates of 0.30 cfm or in your example 6%-9% of the total air leakage (259 sqft windows - 2000 sqft home) is insignificant and a sound energy building practice.

I did not use the words "insignificant and a sound energy building practice." I just gave the percentage of the overall house leakage for the worst case leakage rate, and said that it did not seem too leaky relative to overall house leakage for current building practice.

Regarding DB ratings, what I had stated does not contradict your source from the Garden Web.com blog. I stated in my post that AI is NOT related to DB ratings.

What you actually said was, "So while a DP30 rated window is rated that it will not fail structurally up to 110MPH winds. It is only rated for wind driven rain events up to 40MPH and that is not considering positive and negative pressures that are found throughout a homes wall area. That means it most likely will leak air and rain when the outside wind is at 30MPH or greater."

So first you say that air infiltration is related to DP rating (i.e., a DP30 window will leak a lot of air), and now you realize that it is not.

The Marvin fiberglass gets poor AI ratings and poor DB ratings.

You do not know what the air infiltration rating is, since Marvin has not provided that test result.

Regarding humidity levels. Ideal winter levels would be below 40% but 45% should NOT be causing his window [condensation] problems.

Please do not ask me to explain to you how water vapor condensation works. I provided the partial pressures for the water vapor at the two temperatures of interest clearing showing the driving force for condensation, so I already did the hard part for you.

Posted By Lee Dodge on 02 Dec 2012 08:28 PM

I did not use the words "insignificant and a sound energy building practice." I just gave the percentage of the overall house leakage for the worst case leakage rate, and said that it did not seem too leaky relative to overall house leakage for current building practice.

Please do not ask me to explain to you how water vapor condensation works. I provided the partial pressures for the water vapor at the two temperatures of interest clearing showing the driving force for condensation, so I already did the hard part for you.

For the third and final time, Marvins AI rating is 0.30 cfm or less ( < 0.30cfm). That is according to Marvins Performance Test sheet (AAMA/WDMA/CSA). In other words the windows don't perform that well in terms of AI so they don't post the exact number. I'm pretty sure if they achieved AI ratings of 0.20 or less, they would post the results. If they achieved 0.03 - 0.20 cfm they would be broadcasting it all over the place.

I did notice that they now have optional DP40 and DP50 ratings available for this series. I don't know how much more $$ that would cost but at least they do offer better DP ratings over the DP30.

Why would the condensation freeze on the inside/interior portion of the window frames? I've experienced condensation on windows during winter and NEVER had the water freeze on the interior window frame portion. I don't understand why you are not willing to admit that the problem is beyond high humidity levels and condensation. Why would the water freeze on the inside? The reason it would freeze is because the windows are letting in the outside air and the frigid outside air is making the water freeze. This then is an issue of windows that leak a lot of air.

Wind driven rain is rain that is being forced into the home through the window by means of wind speed. Your post made it quite clear that you believed the air leakage on the windows was not that important. Your position is in opposition by the majority of energy efficient building techniques. Nobody would dismiss air leakage in windows as an insignificant number. Post your statement on GBA and you will see that they will oppose your statement/position.

We will have to agree to disagree...

Using numbers I consider reasonable, I get ~5% of the total house air infiltration caused by good windows*. Last time I did the calculation for the heating cost of air infiltration on a new (.2 ACH nat) house, it was $60/year. So 5% of that is $3/year. I won't be spending too much on tighter windows (ie, better than good).

* - http://commercial.marvin.com/commercial-performance-testing/

We all know lower leakage rate windows are better than higher leakage rate windows for energy conservation. But as jonr says, you have to do some calculations to see if any extra cost associated with the lower leakage rate windows are worth it. Unfortunately, leakage rates for windows made in the U.S. are not easily available (as far as I can tell), in contrast to, for example, U-values, that are available on the NFRC website. So it sometimes takes some guesswork to estimate the effect of leakage on heat losses and the resulting costs.

Is R-20 ceiling insulation better than R-5? Yes, four times better. Is upgrading to R-20 ceiling insulation worth the cost? Yes, almost always. Is R-240 ceiling insulation better than R-60? Yes, four times better. Is upgrading from R-60 to R-240 worth it? No, almost never.

We need window data other than, "these windows are leaky" to make intelligent decisions.

Posted By Lee Dodge on 03 Dec 2012 11:36 AM
We all know lower leakage rate windows are better than higher leakage rate windows for energy conservation. But as jonr says, you have to do some calculations to see if any extra cost associated with the lower leakage rate windows are worth it. Unfortunately, leakage rates for windows made in the U.S. are not easily available (as far as I can tell), in contrast to, for example, U-values, that are available on the NFRC website. So it sometimes takes some guesswork to estimate the effect of leakage on heat losses and the resulting costs.

Is R-20 ceiling insulation better than R-5? Yes, four times better. Is upgrading to R-20 ceiling insulation worth the cost? Yes, almost always. Is R-240 ceiling insulation better than R-60? Yes, four times better. Is upgrading from R-60 to R-240 worth it? No, almost never.

We need window data other than, "these windows are leaky" to make intelligent decisions.

Air leakage in windows is more than a simple one dimensional issue of air leaking into and out of the home via the window. Currently the NFRC does not require window manufacturers to list their AI Ratings on the windows. That is a shame because many windows are poorly designed and leak a lot of air. The consumer has no idea how much air the window leaks. Sit next to a window that has a 0.30 cfm rating on a cold breezy winter day and you will feel the cold air draft coming in.

Let's step back and find out HOW they test for AI Ratings:

" The test window is installed on a large wall. On one side, a vacuum is of 75 pascals (1.57 psf) is applied. This corresponds to approximately a 25 mph wind blowing perpendicularly to the window. Flow meters measure the rate of air leakage. This is divided by the total window area to get a reading (in the U.S) in cfm/ft2 to the nearest tenth (i.e., a test value of 0.17 would be given a rating of 0.2). The best possible rating by the NFRC is 0.1, as they will not round to 0. AAMA does record to 0.01 cfm" 

So what happens when the wind blows ABOVE 25MPH? Of course that window will experience greater air leakage. It's not like the window gets better with increased wind loads. It gets worse. Poor window Air Infiltration ratings becomes a greater percentage of total energy loss as the window’s U-factor becomes higher. This is where the AI rating becomes multi-dimensional. It's no longer simply an air leak issue. Now you have a U-Factor increase in the window. So that window U-Value of 0.30 now becomes a 0.35 or 0.40+, depending on the outside wind speed and temperature.

In addition when the window is leaking air when it's 65F outside will not have the same impact as that window leaking 15F outside air. Therefore, the AI Rating is not a simple one dimensional issue. In real world performance the leaky window will contribute to much higher energy costs for the homeowner.


 because the
energy loss through heat transfer is reduced. Low air infiltration is critical for a passive solar house,
where energy losses must be kept to the absolute minimum. For these houses, casement or Tilt & Turn
windows are the only proper choices, for the reasons stated below.
Are some

Posted By jonr on 03 Dec 2012 10:36 AM

Using numbers I consider reasonable, I get ~5% of the total house air infiltration caused by good windows*. Last time I did the calculation for the heating cost of air infiltration on a new (.2 ACH nat) house, it was $60/year. So 5% of that is $3/year. I won't be spending too much on tighter windows.

* - http://commercial.marvin.com/commercial-performance-testing/

Your analysis is flawed in so many ways that it is ridiculous and it doesn't deserve a response. Congrats on your decision to buy leaky windows!

Who would have thought that people are now promoting leaky windows as sound energy methods on GBT. According to you, buying leaky windows will only cost you $3 more a year.

Good grief, I now can see WHY people stop posting on this forum because of nonsense posts like yours. I can see why GBA is the place to discuss things like this because people like JonR would get laughed off the GBA site for saying such ridiculous statements.

Lbear-

It is time for you to present some actual results for estimated energy savings and cost savings for a lower leakage window versus a "standard" window with worst case leakage of 0.3 cfm/sq ft. Use constant U-factor so that the difference is limited to the infiltration difference. That will allow us to see how much money is saved on a yearly basis that can be applied to a potential extra cost for the lower leakage window. According to my analysis presented above for an 2000 sq ft house with 18% of the wall area in windows, the potential savings look to be fairly small. Please present your numerical results.

According to you, buying leaky windows will only cost you $3 more a year.

Still amusing yourself with things people didn't say. Post your $ numbers or go away.