Letters: March/April 2010

March/April 2010
A version of this article appears in the March/April 2010 issue of Home Energy Magazine.
Click here to read more letters.

Fiberglass Not Filter Glass

I would like to comment on the Bill Lucas letter on insulating cathedral ceilings that appeared in the Nov/Dec ’09 issue of Home Energy (“Insulating Cathedral Ceilings,” p. 3). In his letter Bill refers to fiberglass as “filter glass.” But fiberglass batts are not intended to provide air sealing. Fiberglass batts are very good at filling cavities in order to prevent convection with minimal conductivity. Tests conducted by Johns Manville and others show that overall R-values of walls, floors, or ceilings insulated with fiberglass batts and properly air sealed perform as expected based on the stated R-value of the batts and book values for the R-values of the other components.

Since in most cathedral ceiling and sidewall retrofit applications, it is not possible to air seal the cavities in the same way as a new home, we would agree that you want to use a product that offers both thermal and air resistance benefits.
Tests have shown that JM Spider installed without adhesive has better air resistance properties than cellulose for dense-packing walls or other areas of a home. JM Spider is a specifically designed loose-fill fiberglass for sidewall and constrained attic space installations. The size of the JM Spider fiber is significantly smaller than loose-fill fiberglass products for attics, which allows for better performance. For drill-and-fill-type applications, the optimal density for JM Spider is 2.2 lb per cubic foot. At this density it delivers significantly better R-value (25% better) and air resistance (30% better) than dense-pack cellulose installed at a density of 3.5 lb per cubic foot. JM Spider is also installed at a lower pressure than cellulose, which reduces the risk of damaging a home during installation. And finally, the inherent property of fiberglass fibers to retain their size and shape means JM Spider will not settle over time. This makes JM Spider ideal for weatherization or other retrofit jobs.

John Smith
Platform Leader, Environmental Construction
Johns Manville
Littleton, Colorado

Dual-Flush Retrofit Kits

I am a longtime reader and big fan of your magazine. At recent tradeshows I have seen several dual-flush retrofit kits for older toilets that claim to save water while maintaining performance. Of course, at trade shows these perform perfectly. Do these devices actually work? Have you done any evaluation of these products and their performance? I think this would make a great article for the magazine.

Kris Knutson
Build It Green
Berkeley, California

Author and water efficiency expert John Koeller replies:
At Koeller and Company, we absolutely do not recommend the dual-flush retrofit kits at this point due to problems associated with performance, water use (which may increase, not decrease), and health and safety (failure to restore the required trap seal). A couple of months ago, Bill Gauley of Veritec Consulting in Ontario, Canada, and I sent a caution statement to water agencies and other water providers in the United States and Canada. A testing program is about to begin that will seek to further identify and resolve some of the problems. The testing program is voluntary, and right now we have about one-half of the manufacturers signed up to participate (out of a total of about 12 different manufacturers).

I would urge anyone with thoughts about these devices to consider that water agencies will not subsidize such devices without independently developed evidence that they work as claimed, that they do not endanger health and safety, and that they actually reduce water use. Nor will the WaterSense program consider them as a candidate for labeling until independent testing has been completed.

I am a technical advisor to the international Alliance for Water Efficiency (AWE) and the California Urban Water Conservation Council (CUWCC). Here are some links to helpful information about toilets and water efficiency:

Alliance for Water Efficiency (AWE)


  • www.allianceforwaterefficiency.org
  • www.a4we.org/Maximum_Performance_(MaP)_Testing.aspx  


California Urban Water Conservation Council (CUWCC)

  • www.cuwcc.org/MaPTesting.aspx
  • www.cuwcc.org/resource-center/product-information.aspx
  • www.cuwcc.org/waterlogue-newsletter.aspx

Getting LEDs Right

I agree with the tone and urgency of your plea to manufacturers and the standards community to address the need and prevent the repeat of CFLs racing to the bottom (“LEDs: Avoiding the CFL Debacle,” Jan/Feb ’10, p. 2). This is music to our ears here at PG&E. I would like to share a couple of my observations.

I did want to point out it’s not all doom and gloom. We (most of the California utilities) have put our foot down with early manufacturers and simply state, “Show us the proof of your claims.” It’s been hard to explain to customers and our folks out promoting energy efficiency that we need to exercise some caution and reservation before jumping on board with some of these products. At the same time, though, it’s not fair to—say—be leery of all LED products. DOE and Energy Star have done a good job of setting expectations for certain categories of fixtures to meet our needs. Categories such as recessed downlighting and what we are doing with LED outdoor lighting are working. Bottom line: While I try to downplay the ability of LEDs to be the next great lamp, I don’t want to scare people away and leave the impression that we will never be ready.

Energy Star has circulated a draft proposal for LED replacement lamps that will be of great help to us in managing quality products. Our concern is the time it’s going to take to get this in place and then get products qualified. It’s coming, just not fast enough.

The last thing I wanted to share, which I believe you capture: A lot of product is coming from offshore. We need to make sure it comes into this country meeting our standard or an international standard. I see many people that are lighting vendors getting sucked into false expectations and selling these products to our customers. When we ask them to help us understand their claims, they are often speechless. Standards need to be international, not just at the Energy Star or local level. Having an international standard will only help accelerate the growth of these products for the right reason and lead to persistent savings.

Thanks for taking a stab at this issue.

Dave Alexander
PG&E CEE/Mass Market
San Francisco, California

High-MERV Filters in the Spotlight

Having just finished reading the high-MERV filter article in the Nov/Dec issue (“Is There a Downside to High-MERV Filters?” p. 32), I have a couple of comments. 
While I agree in general with the thrust of the article, that high-efficiency filtration can come with undesirable outcomes in the quest for cleaner air, I feel some important relevant information has been left out. 

Let me begin by stating that HVAC equipment is designed by the manufacturers to be installed with a total system external static pressure of 0.5 inches of water column (WC) for equipment with the cooling coil external to the unit. Units with integral coils are often designed for 0.3 inches of external static pressure (ESP). 

Good duct systems nationwide average 0.2 inches of pressure drop, and the vast majority of duct systems are below good when it comes to pressure drop. Add in the wet coil at 0.27 inches, and you are already at 0.47 inches of pressure drop before you add the filter.

I feel the statement in the article that a pressure drop of at least 0.5 inches should be entered for the filter is just bad advice. Here’s why: When duct system pressure drop with coil and filter included exceeds 1 inch of pressure drop, many problems develop. More energy is consumed by the blower—either through increased run time for permanent split capacitor (PSC) motors or higher-amp draws for electronically commutated (ECM) motors. High static pressures also contribute to equipment failures and lack of occupant comfort. There have been and continue to be failures of ECM blower motors installed in systems with ESP exceeding 1 inch. The cost of the repair is upwards of $1,200. A compressor replacement can exceed $3,000, and a failed heat exchanger can result in personal injury. All of these problems can and do result from low air flow, contributed to by excessive pressure drop at the filter. 

Intentionally choosing a filter that has an ESP of 0.5 inches when clean will lead to increased energy use and costly repairs. 

While Mr. Springer did suggest that one way to mitigate the added pressure drop of high-efficiency filtration is to increase the filter size (lowering the velocity), he does not include information on readily available filters in the 16 inch x 25 inch size that, when tested at the standard velocity, do not have unacceptable pressure drop. 

The author tested many filter types, including one 4-inch Filtrete, but did not test commonly available media or other filters commonly installed by HVAC contractors. The contractor-installed filters would include media filters as manufactured by Aprilaire and Honeywell, and HEPA filters as manufactured by Trane and Carrier. Had they been tested, they would have been shown to have much lower filter pressure drop than those tested.

As one example, an Aprilaire model 2210, which fits the 16 inch x 25 inch test size, has a pressure drop of 0.13 inches WC at 1,400 CFM, as compared to the Filtrete 1500, the only extended-surface media filter the author tested, which tested at 0.5 inches WC pressure drop. 

It also seemed that Mr. Springer was suggesting that, using Manual D and a filter with 0.5 inches of pressure drop, another way to mitigate the associated problems was to increase the size of some of the ducts. All I can say is, that is not the solution to the problem. The solution is, don’t use these filters. Incorporating a high-efficiency, low-pressure-drop filter as mentioned above will be more cost-effective than increasing the size of some of the ducts and will work in both new construction and retrofit applications. Lastly, when working to solve these problems, keep in mind that these pressure drop measurements are with clean filters. They will often add an additional 0.2 inches or more of pressure drop when loaded.

Scott Robinson
via E-mail

Author David Springer replies:
I appreciate Mr. Robinson’s critique of my article, which provides me with the opportunity to make some clarifications. My statement that a filter pressure drop of 0.5 inches should be assumed for MERV 8 or higher filters in Manual D calculations is based on the replacement of a fiberglass filter with a same-size high-MERV filter, and pressure drops measured at the ASHRAE Standard 52.2 test velocity. I should have made it clear that this is not necessarily an acceptable condition, and that the external static pressure capabilities of the equipment must be considered.

I believe the greatest cause for concern is that the low-cost fiberglass filters prevalent in most production homes are likely to be replaced by high-MERV filters purchased from common retailers. Most of the homes with which we have experience use filter grilles or integral filter racks that may be of appropriate size for fiberglass filters, but have inadequate face area to accommodate the higher pressure loss of high-MERV filters.

The inventory in the several stores we visited was dominated by MERV 8 and higher filters, and buyers are justifiably enticed to spend a little more money to obtain better indoor air quality. There are certainly other alternatives. The Aprilaire 2210 filter cited by Mr. Robinson has a 5% larger face area than the filters we tested, and its 6¾-inch depth further helps to reduce pressure loss. Everyone should have one. However, it is not designed for filter grilles; it must be contractor installed; and replacement media are not to be found in retail stores. How many homeowners are cognizant of the importance of spending the $300 or so to have a larger filter installed?

I would enjoy learning from Mr. Robinson what his source of information is regarding ECM blower motor and compressor failures resulting from low air flow. In 17 years of working with the GE ECM in various applications, I have never seen a failure resulting from excessive loading—these motors are well protected. And as I pointed out in the article, condensing-unit performance ratings show small declines in EER over the range of air flow reductions we measured, so it is unlikely that compressor failure would be an expected result of the 10%–15% reduction in air flows we saw with PSC motors and high-MERV filters. This said, I don’t want to diminish the importance of proper filter sizing, which it was the intent of the article to point out.

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