# Wall & window temperature norms

• posted on December 7, 2010, 1:15 am
Anyone know of a source of information on the expected indoor wall and/or window temperatures for a given outdoor temperature.
For example, after dark [i.e. no sun on outdoor wall] with the
Outdoor temp at 32 F, Indoor temp @ 70F (wall temp of interior walls)
The inside of the exterior walls are measuring ~ 63-67 degrees Most of my windows are ~55F [regular glass w/ storm windows]
Trying to decide if this is good, bad, or normal.'delta'
Thanks for any information
Terri Smith
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• posted on December 7, 2010, 3:10 am
Terri Smith wrote:

Omega makes an infrared thermometer optimized to measure building energy losses.
The manual is very informative on the subject.
http://www.omega.com/manuals/manualpdf/M1331.pdf
AS I understand it, you're losing 15 BTU/hr for every square foot of window.
At present, it's 44F outside. Inside walls are at 64F. 2-ply Windows measure 59F behind the curtains.
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• posted on December 7, 2010, 11:39 am
Terri Smith wrote:

Omega makes an infrared thermometer optimized to measure building energy losses.
The manual is very informative on the subject.
http://www.omega.com/manuals/manualpdf/M1331.pdf
AS I understand it, you're losing 15 BTU/hr for every square foot of window.
At present, it's 44F outside. Inside walls are at 64F. 2-ply Windows measure 59F behind the curtains.
====================================Thanks Mike very interesting document
Do you recall what your indoor temp was at the time you took the above readings? Best to compare if you used a wall surface in center of house using same device you used on the other wall
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• posted on December 7, 2010, 4:58 pm
Terri Smith wrote:

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• posted on December 7, 2010, 11:19 pm
Newsgroups: alt.hvac

Yep, and I stated it, "inside walls are at 64F."
===============================Suspect I'm not expressing this very well. From the inside of the house what is the difference in temperature between a wall(s) that have an outside exsposure and a reference wall in center-of-the-house (i.e. no outside exposure on the other side)
Maybe what you're saying is they are well insulated, hence no delta-T
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• posted on December 8, 2010, 5:43 am
Terri Smith wrote:

64.5 inside wall 63 perimeter wall 60 window That's behind a curtain, they warm up somewhat with the curtains open. 41 outside
different day, different temps different walls
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• posted on December 8, 2010, 11:05 am

64.5 inside wall 63 perimeter wall 60 window That's behind a curtain, they warm up somewhat with the curtains open. 41 outside
different day, different temps different walls ====================================Thanks Mike
Even though your just 1 data point, it does tell me that my walls are not as well insulated as yours. .
** Be interesting if some others on the group joined in **
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• posted on December 8, 2010, 10:51 pm
Terri Smith wrote:

with Omega's method. For its intended use, I expect it's sufficient. But here's the rub. Heat loss is proportional to the difference in inside/outside surface temperatures and inversely to the R-value. But, if the surface temperature were the only issue, the air temp and the inside wall temp and the perimeter wall temp would be the same. They're not. There are convections and boundary layers and all kinds of fluid dynamic issues related to the heat getting to the wall. On an inside wall, where the losses are low, it don't matter, cause it equalizes eventually. On the perimeter walls where the loss is high, there's a temperature gradient in the air that messes up the reading. And that gradient is affected by drafts, convection, etc. For two spots in close proximity, the relative info is good. My furnace runs about 5 minutes out of 85. At the end of the off-time I can get 3F difference between the top and bottom of a perimeter wall. All that adds up to imprecise measurements. If I equalize it with a fan, I've created a situation that is not equivalent to conditions of interest.
I covered one window completely with R5 pink rigid foam insulation. My windows are specified at R3.125. I expected to be able to correlate temperature numbers between R3.125 and R8.125. Not so much. The covered window is warmer than I'd expect, but the deltas are small relative to the measurement resolution. Metrology is tough. The better your insulation, the harder it is to measure, and any fixes you implement have increasingly long payback.
I've dabbled in a couple of ways to measure actual heat flow. Problem is that the measurement apparatus disturbs the system. Best looking option at this point is a peltier module like they use in 12V coolers. Stick it on the wall and measure the voltage. Getting repeatable coupling to the wall might be an issue. Thermal time constant is LOOOONG. Need some way to attach it until it stabilizes. Create a small draft by waiving your hand in front of it and the reading changes dramatically. Those pesky air temperature gradients and boundary layers again. Then there's the whole issue of building calibration fixtures to determine what it's really telling me. Simple in theory, PITA in practice.
Omega sells some thin-film sensors that use the same theory and have much shorter thermal time constant. Problem is that they use relatively few junctions and the voltage output at the temperature differentials of interest here is miniscule.
The only thing I'm sure of is, "in winter, if a surface is cold, take steps to make it warmer without expending energy."
My walls suck. They're 2" rock wool from 1971. If yours are worse than mine, you've got no insulation at all ;-(
As for people joining in, you'll have better luck in alt.home.repair
About all you get here are "you're an idiot" and "Hire a professional.. cause you're too stupid to do anything yourself". I've not experienced anything close to education on any subject...electrical engineers are too stupid to comprehend thermodynamics.
There really are some knowledgeable and helpful people lurking here, but you have to endure all the flying insults long enough for them to emerge.
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• posted on December 9, 2010, 2:52 pm

with Omega's method. For its intended use, I expect it's sufficient. But here's the rub. Heat loss is proportional to the difference in inside/outside surface temperatures and inversely to the R-value. But, if the surface temperature were the only issue, the air temp and the inside wall temp and the perimeter wall temp would be the same. They're not. There are convections and boundary layers and all kinds of fluid dynamic issues related to the heat getting to the wall. On an inside wall, where the losses are low, it don't matter, cause it equalizes eventually. On the perimeter walls where the loss is high, there's a temperature gradient in the air that messes up the reading. And that gradient is affected by drafts, convection, etc. For two spots in close proximity, the relative info is good. My furnace runs about 5 minutes out of 85. At the end of the off-time I can get 3F difference between the top and bottom of a perimeter wall. All that adds up to imprecise measurements. If I equalize it with a fan, I've created a situation that is not equivalent to conditions of interest.
I covered one window completely with R5 pink rigid foam insulation. My windows are specified at R3.125. I expected to be able to correlate temperature numbers between R3.125 and R8.125. Not so much. The covered window is warmer than I'd expect, but the deltas are small relative to the measurement resolution. Metrology is tough. The better your insulation, the harder it is to measure, and any fixes you implement have increasingly long payback.
I've dabbled in a couple of ways to measure actual heat flow. Problem is that the measurement apparatus disturbs the system. Best looking option at this point is a peltier module like they use in 12V coolers. Stick it on the wall and measure the voltage. Getting repeatable coupling to the wall might be an issue. Thermal time constant is LOOOONG. Need some way to attach it until it stabilizes. Create a small draft by waiving your hand in front of it and the reading changes dramatically. Those pesky air temperature gradients and boundary layers again. Then there's the whole issue of building calibration fixtures to determine what it's really telling me. Simple in theory, PITA in practice.
Omega sells some thin-film sensors that use the same theory and have much shorter thermal time constant. Problem is that they use relatively few junctions and the voltage output at the temperature differentials of interest here is miniscule.
The only thing I'm sure of is, "in winter, if a surface is cold, take steps to make it warmer without expending energy."
My walls suck. They're 2" rock wool from 1971. If yours are worse than mine, you've got no insulation at all ;-(
As for people joining in, you'll have better luck in alt.home.repair
About all you get here are "you're an idiot" and "Hire a professional.. cause you're too stupid to do anything yourself". I've not experienced anything close to education on any subject...electrical engineers are too stupid to comprehend thermodynamics.
There really are some knowledgeable and helpful people lurking here, but you have to endure all the flying insults long enough for them to emerge. =================================== Thanks Mike
Appreciate the info. Think you're rigth about my walls probably lacking insul. I have a 2 stage HP, on 2 nd stage it can carry the house even at 22 deg, but it runs continuously between 2nd and 1st stage heat so the air in my house never settles. Also I use an IR thermometer so it's not touching the surface when I take the reading. Understand emissivity (memtion in the ref you sent in first msg) but when doing delta-T comparisons, emissivity is a wash.
I don't worry about the "you're an idiot, hire a professional" responses, they're just the silt surrounding the gold nuggets of advice and insight.one finds on these NG's
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• posted on December 9, 2010, 8:57 pm
Terri Smith wrote:

I'd worry about it a little if you use a wall as a reference to measure a window. I did the controlled experiment. For the flat white paint on my walls, glass compares favorably.

the pot to get that nugget to form.