What do those numbers on the manufacturer's stickers in new windows mean?

Wednesday, October 17, 2018

They are energy performance ratings. Here’s a typical sticker you would see on a new window, with the  five performance rating numbers. Letters in blue have been added so that you can reference each rating in sequence in the explanation that follows. Window ratings are certified by the National Fenestration Rating Council (NFRC). The first two performance ratings, U-Factor and Solar Heat Gain Coefficient, are the most important.

  1. The U-Factor is a measure of the insulating ability of the window: how well it prevents heat from entering or escaping through the window. U-Factor ratings generally fall between 0.20 and 1.20. The lower the U-Factor, the better the window is at insulating. To convert a U-Factor to an R-Value (the number used to rate the insulating ability of other building materials), divide 1 by the U-Factor. So, a window with a U-Factor of 0.25 would have an R-Value of 4 (1 divided by 0.25 = 4). A low U-Factor is more important in cold climates, where it is important to keep the heat from escaping .
  2. Solar Heat Gain Coefficient (SHGC) measures how well a window blocks the transmission of heat from the sun through the window. SHGC is expressed as a number between 0 and 1. The lower the SHGC, the better the product is at blocking unwanted heat gain, which is particularly important in hotter, Southern climates like Gainesville where the homes are air conditioned part of the year.
  3. Visible Transmittance (VT) measures how much light comes through the window, and is expressed as a number between 0 and 1. The higher the VT, the higher the percentage of sunlight that penetrates the window for better daylighting.
  4. Air Leakage (AL) measure how much outside air comes into a home through the window. AL rates usually fall between 0.1 and 0.3. The lower the AL, the better the window is at keeping air out. It is an optional rating, and not all manufacturers choose to include it on their labels.
  5. Condensation Resistance (CR) measures how well an window resists the formation of condensation. It is expressed as a number between 1 and 100, with higher numbers indicating better resistance to condensation on the window. 

    For more details about the rating system, visit the NFRC website at: http://www.nfrc.org/. Also, see our blog post What are the small slots at the bottom of the outside of my window?

• • • • • • • • • • • • • • • • • • • • • • • • • • • 

  To learn more about doors and windows, see these other blog posts:

What causes sweating (condensation) on the inside of windows in the winter? 

Is every exterior door of a house required to have a landing outside?  

Why does condensation form on the outside of some windows and not others in the morning? 

Why if the garage door track a white tube? 

What is the raised metal plate on the floor under the garage door?

 Why do I have to hold down the button to close the garage door? 

 Where is safety/tempered glass required for the windows of a house?

How can I tell if a window or glass door is safety glass? 

Should a front door swing in or out? 

Why is pressure washing double pane windows an expensive mistake? 

How many exit doors are required for a house?

 How many exit doors are required for a mobile/manufactured home? 

Are openable windows required to have window screens? Will windows with no screens pass a home inspection? 

Can a bedroom door open into the garage?

What are the building code requirements for a door from the garage to the house?

What is "low-E" window glass? 

What does ANSI 297.1 on glass mean?

Why is a double cylinder deadbolt lock on an exterior door a safety hazard?

How can I check my garage door to make sure it is safe?  

What is an egress window?

Does a home inspector test all the windows and doors in a home? 

How difficult is it to change a window to french doors or a sliding glass door?

How do you determine if a door is left-handed or right-handed?

Why are window security bars dangerous? 

What are the common problems you find inspecting windows?

What is causing a foggy haze on my windows? 

What does a home inspector check on an electric garage door? 

• What is the tempered label on glass at windows and sliding glass doors called?

• Do I need to have two exterior exit doors in my house? 

• When is safety glass required for windows at stairs and stair landings?

    Visit our DOORS AND WINDOWS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.


Sample label above from - National Fenestration Rating Council


How To Look At A House

McGarry and Madsen's home inspection blog for buyers of  

site-built, mobile/manfuactued and modular homes

(placeholder)

Search

This

Site

Search

This

Site

Attics

Air Conditioner & Furnace Age

AFCI, CAFCI, DFCI, & GFCI

Bathrooms

Aging in Place

Appliances

Click Below  

for Links to Collections

of Blog Posts

by Subject

Cracks

Doors and Windows

Electrical

Energy Efficiency

Fireplaces and Chimneys

Heating and Air Conditioning

Home Inspection

Hurricane Resistance

Electric Receptacle Outlets

Electric Panels

Garages and Carports

Common Problems

Exterior Walls & Structures

Insulation

Insurance

Life Expectancy

Mobile/Manufactured Homes

Older and Historic Houses

Mold, Lead & Other Contaminants

Modular Homes

Metal Roofs

Plumbing

Radon

Pool and Spa

Roof and Attic

Remodeling

Safety

Site

"Should I Buy A..."

Stairs

Termites, Wood Rot & Pests

Structure and Rooms

Wells

Water Heaters

Water Heater Age

Septic Tank Systems

Plumbing Pipes

Sinkholes

When It First Became Code

Park Model Homes

Shingle Roofs

Stucco

Wind Mitigation Form

"Does A Home

Inspector...?"

"What Is The Difference Between..."

Brick

Concrete and Concrete Block

Foundations

4-Point Inspections

Rain Gutters

Condominiums

Crawl Spaces

Building Permits

Clay Soil

Floors

Toilets

Generators

HUD-Code for Mobile Homes

Flat Roofs

Sprinkler Systems

4-Point Inspections

Frequently Asked Questions (FAQ)

Building Codes

Inspector Licensing

& Standards