Weird(?) heating system temperatures

Piwoslaw · 10-25-11, 01:59 PM

Lately I've been running around the house with my IR thermometer and I noticed something which struck me as funny. The input and output pipes of my boiler were cooler than the pipes farther away. Here is a sketch:

The temperatures are in °C. The length of pipe from the bottom of th boiler to the T-intersection is 1 meter (cool return) and 2 meters (hot supply). I added the pipe diameters (in mm) in case they might have an influence on temps. Would the water in the smaller diameter pipes be cooler because it's moving faster? The basement temperature is ~14°C if that helps any.

strider3700 · 10-25-11, 02:14 PM

how accurate is the IR thermometer? Having played around with my "cheap" one 2-3 degrees C is within it's margin of error.

Ryland · 10-25-11, 04:40 PM

With an IR thermometer make sure that the surface that you are measuring is the same, some people will scrub the pipe down then put a single layer of black tape on to get an accurate reading.
With the cold return, remember that heat rises so of course the top is going to be hotter then the bottom.

Xringer · 10-25-11, 08:28 PM

If you are reading from a distance, the larger pipe is going to fill more of the sensor's coverage area.
The smaller pipe will register more of the back-ground temps behind the pipe..

You might need to get in close..

Piwoslaw · 10-26-11, 12:29 AM

So it might be the IR thermometer? I'm not sure how accurate it is, but I try to hold it 5-10cm from the target to make sure it has a good view. At distances of 20-30cm the readings jump around, but below 10cm they are stable.

I admit that the pipes are painted differently, so I'll stick some black tape to the measurement points. Does an object's color effect the IR's readings?

Quote:

Originally Posted by Ryland

With the cold return, remember that heat rises so of course the top is going to be hotter then the bottom.

I thought that the circulation pump would keep the temperature evenly distributed? Or maybe the top pipes are so big that the pump will suck the cooler water down, leaving the warmer water at the top.

Xringer · 10-26-11, 06:42 AM

Keep getting in closer, until you see a max reading.

I used black tape on the glass of some windows, and put the muzzle of the sensor in contact with the tape. Got consistent readings.

Color will affect some readings a little. Because of reflected back-ground energy.

MN Renovator · 10-26-11, 05:23 PM

IR thermometers are fun but can also be very inaccurate if they are gathering from a reflective surface, people use electrical tape because it doesn't reflect the light or accept reflected light well because its flat and non-glossy. One other thing to keep in mind that I've seen people make when they decided to pick up my IR thermometer is the laser, if it has one, is usually off the mark quite a bit. If I'm aiming at something a cars length away it might be useful but if my friend tries to use it to measure the temperature of another friends' tongue they are actually aiming at their nose and wondering why that person is giving temperature results that would be expected in correlation with hypothermia. With my IR thermometer you can clearly see there is no way that the spot marks the measurement area unless there is some decent distance. I usually take the spot I'm trying to measure and aim a little up, down, left, and right until I find the highest or coldest temperature I can find, depending on whether I'm trying to find the coldest spot on the ductwork during air conditioning(tried to find out the temp drop as close as I could without actually opening anything up, probably not too accurate tho) or the hottest spot of a surface.

Hope that helps.

10-25-11, 01:59 PM	#1
Piwoslaw Super Moderator Join Date: May 2009 Location: Warsaw, Poland Posts: 961 Thanks: 188 Thanked 110 Times in 86 Posts	Weird(?) heating system temperatures Lately I've been running around the house with my IR thermometer and I noticed something which struck me as funny. The input and output pipes of my boiler were cooler than the pipes farther away. Here is a sketch: The temperatures are in °C. The length of pipe from the bottom of th boiler to the T-intersection is 1 meter (cool return) and 2 meters (hot supply). I added the pipe diameters (in mm) in case they might have an influence on temps. Would the water in the smaller diameter pipes be cooler because it's moving faster? The basement temperature is ~14°C if that helps any. Attached Thumbnails __________________ Ecorenovation - the bottomless piggy bank that tries to tame the energy hog.

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10-25-11, 02:14 PM	#2
strider3700 Master EcoRenovator Join Date: Dec 2008 Location: Vancouver Island BC Posts: 745 Thanks: 23 Thanked 37 Times in 30 Posts	how accurate is the IR thermometer? Having played around with my "cheap" one 2-3 degrees C is within it's margin of error.

10-25-11, 04:40 PM	#3
Ryland Master EcoRenovator Join Date: Mar 2009 Location: Western Wisconsin. Posts: 913 Thanks: 127 Thanked 82 Times in 71 Posts	With an IR thermometer make sure that the surface that you are measuring is the same, some people will scrub the pipe down then put a single layer of black tape on to get an accurate reading. With the cold return, remember that heat rises so of course the top is going to be hotter then the bottom.

10-25-11, 08:28 PM	#4
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	If you are reading from a distance, the larger pipe is going to fill more of the sensor's coverage area. The smaller pipe will register more of the back-ground temps behind the pipe.. You might need to get in close..

10-26-11, 06:42 AM	#6
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	Keep getting in closer, until you see a max reading. I used black tape on the glass of some windows, and put the muzzle of the sensor in contact with the tape. Got consistent readings. Color will affect some readings a little. Because of reflected back-ground energy.

10-26-11, 05:23 PM	#7
MN Renovator Less usage=Cheaper bills Join Date: Nov 2010 Location: Minneapolis, MN Posts: 939 Thanks: 41 Thanked 116 Times in 90 Posts	IR thermometers are fun but can also be very inaccurate if they are gathering from a reflective surface, people use electrical tape because it doesn't reflect the light or accept reflected light well because its flat and non-glossy. One other thing to keep in mind that I've seen people make when they decided to pick up my IR thermometer is the laser, if it has one, is usually off the mark quite a bit. If I'm aiming at something a cars length away it might be useful but if my friend tries to use it to measure the temperature of another friends' tongue they are actually aiming at their nose and wondering why that person is giving temperature results that would be expected in correlation with hypothermia. With my IR thermometer you can clearly see there is no way that the spot marks the measurement area unless there is some decent distance. I usually take the spot I'm trying to measure and aim a little up, down, left, and right until I find the highest or coldest temperature I can find, depending on whether I'm trying to find the coldest spot on the ductwork during air conditioning(tried to find out the temp drop as close as I could without actually opening anything up, probably not too accurate tho) or the hottest spot of a surface. Hope that helps.