Talk:Thermal transmittance

Typical Thermal Transmittance Values
Perhaps I have done the calculation wrong, but I calculate the transmittance of 4mm single-glazed glass to be about 260 W/m^2K. The calculation is as: 1.05 W/mK × 0.004 m = 262.5 W/m^2K.

Have I made a mistake? This is very different from the 5 W/m^2K shown in the article. That would be a pane of glass about 20 cm thick, wouldn't it? 1.05 W/mK ÷ 5 W/m^2K = 0.21 m

Regardless, none of the sources point to where these values came from.

Cheers! Prymal (talk) 16:45, 11 December 2014 (UTC)


 * I didn't do any calculations myself, but I agree that these values need citations. I found this document that more or less agrees with the values in the article though: Default U-values Mariusoei (talk) 07:42, 27 March 2018 (UTC)

Equation is wrong
I think this equation

Φ = A × U / (T1 - T2)

is all wrong. First of all if the article is about thermal transmittance, which we say is the u-value, then why do we not isolate for u-value on the LHS? Secondly, if Φ is the heat transfer is watts, then why does it reduce as the temperature difference (T1 - T2) increases?

The correct equation should be

Φ = A × U × (T1 - T2)

I feel like this is a major mistake and should be correctly urgently. Perhaps we could use some sort of \dot{Q} or dQ/dt notation too, instead of phi, to signify that heat transfer is a rate.

"Orders of magnitude (thermal transmittance)" listed at Redirects for discussion
An editor has asked for a discussion to address the redirect Orders of magnitude (thermal transmittance). Please participate in the redirect discussion if you wish to do so. Utopes (talk / cont) 23:38, 11 April 2020 (UTC)

"Watt per square metre-Kelvin" listed at Redirects for discussion
An editor has asked for a discussion to address the redirect Watt per square metre-Kelvin. Please participate in the redirect discussion if you wish to do so. Utopes (talk / cont) 23:39, 11 April 2020 (UTC)

U-value vs λ-value
So in one spot, the article uses λ-value as "W/mK", and in another spot it uses U-value as "W/m^2*K", which one is it? i've never seen thermal conductivity written as "W/mK" except for in these structural/architectural data sheets, and my spidey senses are telling me that either 1 it's not clear on this page or 2 the entire industry doesn't understand thermal units of conductivity (since what you're measuring isn't per the width of the material, it's per the area (unless you're doing a proof of concept for a material, in which i could imagine it as per volume, which could be simplified as "per width" but just seems unnecessarily jargon-y)). also i don't see why you would need to even write λ in the table?? like more questions than answers over here

basically, i'm asking someone with the industry knowledge to just run through and clear this up/explain it for us plebs - Acetoe (talk) 03:42, 19 December 2023 (UTC)