Low-E Film or Window Replacement?

INFORMATION COURTESY OF THE NATIONAL
FENESTRATION RATING COUNCIL
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When you see an NFRC rating on a window or film, you can be sure the product lives up to the manufacturer’s claims. But what does that rating really mean? NFRC condenses these criteria onto one product sticker:

A.   U-factor: How well a product prevents heat from escaping.

B.   Solar heat gain coefficient: How well a product blocks heat caused by sunlight, as expressed by the amount of solar radiation that passes through a window.

C.   Visible transmittance: How much visible light is transmitted through the product.

D.   Air leakage: This optional rating shows how many cubic feet of air can pass through a square foot of window area. A low leakage rating shows that less air will pass through cracks in the window assembly.

E.   Condensation resistance: This optional rating measures how well a product resists forming condensation on its interior surface (not shown).

1. Diagnose the Problem
   Examine your existing windows. You need to replace them if they leak moisture or air, the space between the panes is fogged up (indicating condensation and moisture intrusion), or the seals have failed.
   
   However, tenant complaints may be the first sign something is wrong, explains Steve DeBusk, global energy solutions manager for film manufacturer Solutia Performance Films. If tenants complain of unpleasant conditions, it’s worth determining the cause.
   
   “People feel uncomfortable when there’s too much solar heat gain or glare,” DeBusk says.


2. Balance First and Future Costs
   For some, the choice comes down to which is the bigger priority – less costly low-e window film over the existing windows vs. new high-performance windows that save more energy and enhance the building’s value.
   
   Film reduces solar heat gain, some winter heat loss, and damaging UV radiation. It’s less expensive than replacing the entire window and less disruptive during installation. DeBusk estimates film at $5-$10 per square foot, vs. $40+ for new windows.
   
   However, new windows last longer, are less susceptible to damage during cleaning, and offer broader benefits and more improved performance. These factors may justify the cost, especially if your current windows are nearing the end of their lifecycle.
   
   “For windows older than 15 to 20 years, property managers can often use repair and alteration funds to offset the cost of replacing them,” says Nils Petermann, program manager for the Efficient Windows Collaborative.


3. Seek Answers from Manufacturers
   The variety of films and windows on the market demands a close look at your climate, budget, occupant needs, window size, and orientation. Ask yourself these questions:
   • How much solar heat gain do you want? Consider the local climate.
   • How should the glass look and perform? Tints, coatings, thicknesses, and strengths can all affect performance.
   • Which window frame do you need? Frames affect windows’ insulating and structural properties.
   • How tight should the building be? A low U-factor rating indicates better insulation properties.
   • How much light do you need in the space? Consider visible light transmittance ratings.
4. Look at the Labels
   Check manufacturer specifications to ensure the product fits your building. The wrong film can absorb too much heat and cause thermal stress that breaks the glass. A good warranty is imperative, DeBusk adds.
   “Most window films have a 10- to 15-year warranty,” DeBusk explains. “It’s rare for the glass to break, but all manufacturers have breakage and seal failure in their warranties.”
   
   Also check products for ratings from the National Fenestration Rating Council (NFRC). “The biggest red flag is when windows show up to a job site with no labels on them,” says Tom Herron, communications and marketing manager for the NFRC. “Without the label, you can’t be sure that it will perform the way it’s advertised.“

Janelle Penny ([email protected]) is associate editor of BUILDINGS.