A gasket's thermal conductivity and an installed door's U-factor are different kinds of evidence. Schlegel advertises 0.04 W/(m·K) at 0 °C for its Q-LON timber window/door seal range. That is the manufacturer's bounded material/range statement, not an independently established whole-door energy rating for a particular assembly.
Read the number together with its unit and test scope
Schlegel's statement is a thermal-conductivity figure associated with a seal range. DOE describes U-factor as thermal transmittance of fenestration products and identifies it, together with solar heat gain coefficient, as a major product energy-efficiency metric. The values answer different questions and cannot be equated by dropping their units.
The National Fenestration Rating Council explains that its U-factor is a rated performance characteristic of a window or door product, and it presents a distinct door-label explanation. The label is about the product rating, not simply the material name of one gasket.
| Evidence you have | Correctly scoped question | Unsupported shortcut |
|---|---|---|
| Seal maker's W/(m·K) number | What conductivity figure does this seal supplier advertise at the stated condition? | 'My whole door has this U-factor' |
| NFRC door product label | What certified rating applies to the identified product/configuration? | 'Any door with this gasket gets the same rating' |
| Air movement felt around sash or frame | Where should air leakage be checked? | 'A single conductivity number proves the leak is fixed' |
DOE separately emphasizes drafts and low air-leakage rates in product selection guidance; a U-factor alone is not a substitute for locating an air gap.
A three-record worksheet
Record (1) the exact seal SKU and its document/condition, (2) the door model and glass configuration if supplied, and (3) any actual NFRC door rating or test report tied to that assembled product. If only a generic manufacturer seal page is available, mark the installed door rating unknown. If only the door label exists, do not reverse-engineer a gasket conductivity from it.
Do not calculate projected utility savings from the advertised 0.04 number; neither an assembly model nor a verified leakage-change measurement is established by the cited seal page. For an energy-selection decision, request the actual product label or appropriate assessment, not an invented conversion between W/(m·K) and a whole-door U-factor.
Sources and references
— www.schlegel.com · Timber window & door weatherseals | Schlegel Q-LON & Aquamac · Schlegel official timber Q-LON/Aquamac page Key Benefits > Thermal conductivity · https://www.schlegel.com/products/qlon-seals/aquamac-timber-window-door-seals/— www.energy.gov · Purchasing Energy-Efficient Residential Windows, Doors, and Skylights · DOE FEMP acquisition guidance updated December 2021; Determine Efficiency and Air Leakage sections · https://www.energy.gov/cmei/femp/purchasing-energy-efficient-residential-windows-doors-and-skylights— www.energy.gov · Purchasing Energy-Efficient Residential Windows, Doors, and Skylights · DOE FEMP acquisition guidance updated December 2021; Determine Efficiency and Air Leakage sections · https://www.energy.gov/cmei/femp/purchasing-energy-efficient-residential-windows-doors-and-skylights— nfrc.org · NFRC Window Label / Door Label / Product Ratings · NFRC homepage label explainer > U-factor, door label, Air Leakage, undated · https://nfrc.org/