SettingsSettings for this calculationUS
The wall or roof area the bridges belong to, measured the way its U-value is.
The heat loss of the bridges divided by this area is what they add to the element's U-value.
The clear-field U-value, before any junction or bracket is counted.
With it, the page adds the bridges' share and gives the effective U-value of the element as built.
The junction's ψ-value, from a certified detail, a model or a published catalogue.
Heat lost per unit length of the junction for each degree of difference, over and above what the plane U-values count: a window reveal, a floor edge, a parapet, a corner.
The length of that junction on this element.
Measured along the junction — the perimeter of every window for a reveal, the run of the slab edge for a floor junction.
The junction's ψ-value, from a certified detail, a model or a published catalogue.
Heat lost per unit length of the junction for each degree of difference, over and above what the plane U-values count: a window reveal, a floor edge, a parapet, a corner.
The length of that junction on this element.
Measured along the junction — the perimeter of every window for a reveal, the run of the slab edge for a floor junction.
The junction's ψ-value, from a certified detail, a model or a published catalogue.
Heat lost per unit length of the junction for each degree of difference, over and above what the plane U-values count: a window reveal, a floor edge, a parapet, a corner.
The length of that junction on this element.
Measured along the junction — the perimeter of every window for a reveal, the run of the slab edge for a floor junction.
The junction's ψ-value, from a certified detail, a model or a published catalogue.
Heat lost per unit length of the junction for each degree of difference, over and above what the plane U-values count: a window reveal, a floor edge, a parapet, a corner.
The length of that junction on this element.
Measured along the junction — the perimeter of every window for a reveal, the run of the slab edge for a floor junction.
The χ-value of one bracket, clip or fixing, from its manufacturer's model.
Calculated to BS EN ISO 10211 for that bracket in its tested build-up; a different clip changes the number even when the drawing does not.
How many of those brackets or clips cross the insulation on this element.
The count from the fixing grid you settled on.
A second kind of point bridge — a balcony connector, a canopy fixing.
Enter its own χ-value and count.
How many of the second kind.
Zero if there is only one kind of point bridge.
Heat loss through the thermal bridges
10.41 BTU/hr·°F
The bridges' heat loss per degree is Σψ × L + Σχ; divided by the element's area it is what they add to the U-value. Multiply the total by a temperature difference for the heat itself.
- From the junctions (ψ × length)
- 7.57 BTU/hr·°F
- From the point bridges (χ × count)
- 2.84 BTU/hr·°F
- Added to the U-value by the bridges
- 0.01 BTU/(hr·ft²·°F)
- Effective U-value with the bridges
- 0.04 BTU/(hr·ft²·°F)
They open the calculator with your figures already in it
Thermal Bridge Heat Loss Calculator (ψ and χ Values): 10.41 BTU/hr·°F — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- BS EN ISO 14683, Thermal bridges in building construction — Linear thermal transmittance; BS EN ISO 10211, Heat flows and surface temperatures — Detailed calculations: the heat loss of the bridges is Σψ × L + Σχ
- BRE BR 497, Conventions for calculating linear thermal transmittance and temperature factors
- ANSI/ASHRAE/IES Standard 90.1-2022, Section 5.5.5 and Appendix A Table A10.1: linear (ψ, Btu/h·ft·°F) and point (χ, Btu/h·°F) thermal bridges
Inputs used
- Area of the Element
- 1080 sq ft
- U-Value of the Element Without the Bridges (0 to skip)
- 0.04 BTU/(hr·ft²·°F)
- Junction 1: Linear Thermal Transmittance ψ
- 0.03 BTU/hr·ft·°F
- Junction 1: Length
- 130 ft
- Junction 2: Linear Thermal Transmittance ψ (0 if none)
- 0.06 BTU/hr·ft·°F
- Junction 2: Length
- 66 ft
- Junction 3: Linear Thermal Transmittance ψ (0 if none)
- 0 BTU/hr·ft·°F
- Junction 3: Length
- 0 ft
- Junction 4: Linear Thermal Transmittance ψ (0 if none)
- 0 BTU/hr·ft·°F
- Junction 4: Length
- 0 ft
- Point Bridges: Point Thermal Transmittance χ
- 0.06 BTU/hr·°F
- Point Bridges: How Many
- 50
- Second Point Bridge: χ (0 if none)
- 0 BTU/hr·°F
- Second Point Bridge: How Many
- 0
Intermediate steps
- From the junctions (ψ × length)
- 7.57 BTU/hr·°F
- From the point bridges (χ × count)
- 2.84 BTU/hr·°F
- Added to the U-value by the bridges
- 0.01 BTU/(hr·ft²·°F)
- Effective U-value with the bridges
- 0.04 BTU/(hr·ft²·°F)
Confidence note: The bridges' heat loss per degree is Σψ × L + Σχ; divided by the element's area it is what they add to the U-value. Multiply the total by a temperature difference for the heat itself.
What this calculation does not cover
- The ψ- and χ-values are inputs, and they are only as good as their source: a certified detail, a model to BS EN ISO 10211 for that construction, or a published catalogue for a similar one. A default value from a table is usually larger than a modelled one, on purpose.
- A continuous girt or stud is not a point bridge; it is usually handled as a reduced layer resistance, which the thermal bridging calculator computes.
- ψ-values depend on which dimensions the U-values were measured to — internal or external — and must be used with areas measured the same way.
Add the equipment this sizes
This result is a specification — 10.41 BTU/hr·°F — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-22 · v1.0.0
Regulatory standards & verification citations3
- BS EN ISO 14683, Thermal bridges in building construction — Linear thermal transmittance; BS EN ISO 10211, Heat flows and surface temperatures — Detailed calculations: the heat loss of the bridges is Σψ × L + Σχ
- BRE BR 497, Conventions for calculating linear thermal transmittance and temperature factors
- ANSI/ASHRAE/IES Standard 90.1-2022, Section 5.5.5 and Appendix A Table A10.1: linear (ψ, Btu/h·ft·°F) and point (χ, Btu/h·°F) thermal bridges
Which documents these citations point at
Standards referenced: ISO 14683, ISO 10211 (International Organization for Standardization, International).
Cite this page
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