Door Manufacturer in China for Global Projects
No. PU or EPS can contribute to the thermal design of a steel door, but the core material alone does not determine the U-value of the complete door.
A whole-door U-value can be affected by:
Air leakage around an installed door is also important to occupant comfort and energy use, but it is not the same property as thermal transmittance.
The responsible purchasing principle is:
Core data can support material selection. A whole-door U-value requires evidence for the complete door construction.
U-value describes thermal transmittance: the rate of heat flow through a building element for a given temperature difference and area. In SI units, it is normally expressed in W/(m²·K).
A lower U-value generally indicates less heat transfer through the evaluated construction under the stated method.
For a pedestrian door, the evaluated construction is not only the centre of the insulated leaf. It may include the door leaf or opaque panel, frame and the thermal effects of their junctions.
ISO 10077-1:2017 specifies methods for calculating the thermal transmittance of windows and pedestrian doors consisting of glazed and/or opaque panels fitted in a frame. ISO 10077-2:2017 addresses numerical calculation of frame profiles and the linear thermal transmittance of their junctions with glazing or opaque panels.
Complete doors can also be measured. ISO 12567-1:2010 specifies a hot-box method for measuring the thermal transmittance of a door or window system and includes the effects of frames, door leaves, panels and fittings.
These scopes show why a core datasheet cannot automatically be converted into a finished-door U-value.
Buyers may receive several different thermal figures. Each answers a different question.
| Metric | What it describes | Typical unit | What it does not prove by itself |
|---|---|---|---|
| Thermal conductivity, λ | Heat conduction through a particular material | W/(m·K) | Whole-door performance |
| Thermal resistance, R | Resistance of a defined layer or construction | m²·K/W | Complete installed opening performance unless its scope covers it |
| Thermal transmittance, U | Heat flow through a defined building element or system | W/(m²·K) | Air leakage or universal performance for different configurations |
A PU or EPS supplier may provide a thermal-conductivity value for its material. That information can help with engineering calculations, but it does not include every steel path, frame section, joint, hardware cut-out or seal in the finished door.
The smaller material number must not be copied into a quotation and presented as the U-value of the complete door.
Steel is structurally useful, durable and suitable for precise fabrication. It is also highly conductive compared with insulation materials.
In a steel door, heat may bypass the main core through:
These paths are commonly described as thermal bridges. Their influence depends on the exact geometry and material connections.
As a result, two doors with the same PU or EPS thickness can have different whole-door U-values if their edge, frame, reinforcement or threshold designs differ.
Not automatically at the complete-door level.
The thermal properties of a specific PU or EPS product depend on its formulation, density, manufacturing condition, thickness, ageing and applicable test data. Even if one selected core product has a lower declared thermal conductivity than another, the final door can still be affected by the rest of the construction.
For example, a PU-filled leaf with continuous steel bridging and a highly conductive frame may not achieve the expected whole-door result. An EPS-based door with a different frame and edge design may behave differently.
Without comparable whole-door evidence, the responsible statement is:
PU and EPS are both insulation-oriented core options. Their contribution must be evaluated within the complete door system.
It is not responsible to state:
PU doors always have a specific U-value, or every PU door is more energy-efficient than every EPS door.
Increasing core thickness can support an insulation strategy, but external leaf thickness is not a whole-door rating.
A thicker door may still contain:
This explains why buyers should not compare doors only by “70 mm,” “90 mm” or another nominal leaf thickness.
The relevant question is:
What complete construction achieved the declared U-value, and does the quoted door match it?
The exact core product, density, thickness, fit and continuity matter. Voids, incomplete foaming, settlement or poor bonding can create inconsistent heat-flow paths.
Skin thickness, internal stiffeners, edge channels and reinforcement around hardware can create conductive paths through the leaf.
The way the inner and outer steel skins meet at the edges can materially affect thermal bridging.
The frame is part of the evaluated door system. Its material, profile, cavities, reinforcements and any thermal-break strategy may influence the result.
Threshold geometry and material can create a strong heat-flow path. The threshold also interacts with bottom sealing and site installation.
Adding a vision panel changes the thermal construction. Glass type, spacer, frame and edge details must be included in the applicable evidence.
Locks, smart-lock cable channels, viewers, handles and other cut-outs interrupt the leaf construction and may require local reinforcement.
The relative areas of leaf, frame and glazing change with size. A value obtained for one configuration should not automatically be transferred to a different single- or double-leaf door.
U-value describes heat transfer through the evaluated door construction. Air leakage describes uncontrolled air passing through or around the product under a pressure difference.
A door can have an insulation-oriented core but still allow drafts through:
ISO 10077-2 explicitly excludes heat transfer caused by air leakage from its numerical frame calculation scope. In North American rating practice, the National Fenestration Rating Council also lists U-factor and air leakage as separate performance categories.
Buyers should therefore request the applicable thermal-transmittance evidence and the applicable air-leakage evidence separately when both properties are required.
Whole-door thermal performance may be established through an accepted calculation route, a physical measurement route or another method required by the project.
Calculation can model the door leaf, frame and junctions using defined material properties and geometric details. The method, assumptions, input data and evaluated configuration must be controlled.
ISO 10077-1 provides a general calculation route for windows and pedestrian doors. ISO 10077-2 provides a numerical method for frame profiles and relevant junctions.
A hot-box test measures the thermal transmittance of a complete door or window system under controlled conditions. ISO 12567-1 includes the effects of door leaves, frames, panels and fittings within its scope.
The buyer should not accept a number without knowing:
90 mm PU-filled steel door, excellent thermal insulation.
This describes a material and nominal thickness but provides no measurable complete-door result.
Insulation-oriented steel door with a specified PU core. Whole-door U-value has not been declared unless separately supported by an applicable calculation or test report for the quoted leaf, frame, threshold, size and glazing configuration.
Complete door U-value of [declared value], determined under [standard and edition], for [defined door configuration], subject to the report scope and permitted variations.
The final version should only be used when the supporting evidence has been reviewed.
TOF DOOR uses EPS in selected constructions, including products supplied for European-market business, and PU in selected higher-end steel doors. These are legitimate core options, but TOF does not treat the material name as a whole-door thermal rating.
At present, TOF does not have a confirmed whole-door U-value, R-value or thermal-conductivity report approved for public use. We can explain the design logic and develop project-specific constructions, but we should not publish a quantified whole-door thermal result without suitable evidence.
For a project with a thermal-performance requirement, the correct sequence is:
This prevents a common sourcing error: buying a “PU insulated door” and assuming that the core description proves compliance with a whole-door requirement.
PU and EPS can support an insulated steel-door design, but neither material determines the complete door’s U-value by itself.
The core, steel edges, reinforcement, frame, threshold, glazing and fittings must be evaluated together. Air leakage must also be treated as a separate performance issue.
Do not convert a core datasheet into a door U-value. Verify the complete construction and the applicable evidence.
No. The exact PU product can contribute to thermal performance, but the whole-door result also depends on the steel construction, frame, threshold, size, glazing, fittings and evaluation method.
Not automatically at the complete-door level. Material properties must be compared using relevant product data, while whole-door performance requires comparable evidence for the finished configurations.
Not necessarily. Nominal thickness does not define thermal bridges, core continuity, frame performance, threshold design or air leakage.
No. U-value describes heat transfer through the evaluated construction. Air leakage measures air passing through or around the product under specified conditions.
No. Thermal conductivity describes the material. Whole-door U-value covers a defined door system under the applicable method.
Yes, when evaluating complete pedestrian-door thermal transmittance under methods such as ISO 10077-1 or ISO 12567-1, the frame is part of the system scope.
