Question 1

Is a lower U-factor better?

Accepted Answer

Yes. A lower U-factor means less heat moves through the door, which means better insulation and more stable indoor temperatures. The same is true for U-value: lower is better for both measurements.

Question 2

What is U-factor?

Accepted Answer

U-factor is thermal transmittance, expressed in Btu/(h·ft²·°F), measured by physically testing a complete installed door assembly under ANSI/DASMA 105. It is the industry standard for rating a garage door's real-world thermal performance.

Question 3

What is U-value?

Accepted Answer

U-value describes heat transfer at a single point in a door, typically a section or slat, calculated rather than tested. It is commonly treated as another way of stating R-value, since both describe thermal resistance from opposite directions.

Question 4

Is U-factor the same as U-value?

Accepted Answer

No. U-value is a calculation limited to a single section of the door. U-factor is a physical test of the entire installed assembly, including hardware, joints, and seals. Two doors with similar U-values can still have different U-factors once the whole door is tested.

Question 5

What is the difference between U-factor and R-value?

Accepted Answer

R-value measures thermal resistance for a door section using a formula based on assumed conditions. U-factor is a direct physical test of the complete door. DASMA's technical guidance states that, for garage doors specifically, U-factor and R-value are not simple reciprocals because they measure different scopes of the same door.

Question 6

How is U-factor tested for garage doors?

Accepted Answer

Under ANSI/DASMA 105, which is based on ASTM E1423, a complete door is installed at an independent lab, one side is held at a constant temperature, the other side is cooled, and the rate of heat transfer between the two sides is measured directly.

Question 7

Does U-factor testing apply to rolling steel doors the same way as sectional doors?

Accepted Answer

The testing standard, ANSI/DASMA 105, applies to both. DASMA's Thermal Performance Verification Program and its verification badge currently cover sectional doors with 16% window area or less and do not extend to rolling steel or high-speed doors, even when those doors carry a tested U-factor.

Question 8

What is a good U-factor for a commercial garage door?

Accepted Answer

It depends on the door type, the application, and any energy code the project needs to satisfy, so there is no single number that fits every project. As a reference point for how the scale works, DASMA notes that a door rated 0.20 is twice as efficient as one rated 0.40.

Question 9

Why do commercial building codes care about U-factor?

Accepted Answer

ASHRAE Standard 90.1, which many commercial energy codes reference, requires door U-factors developed through NFRC 100 whole-product testing procedures for code compliance, and compliance software such as COMcheck documents that same U-factor data. If a U-factor was not developed that way, the code's own default values may apply instead.

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