Infra red thermometer on CH

[Bill]

I am trying to investigate our inherited central heating pipework and have some sort of go at balancing the system, I suspect there is some peculiarity in the system, which was installed and altered in at least 3 separate stages.

I read on the internet that an infra-red thermometer might be handy to measure in and out temperatures at radiators. Maplin have one on offer, so I'm now a proud owner.

In general it seems to work well. It doesn't seem terribly accurate, but amply good enough for what I want.

The mainly inaccessible pipework here is mostly painted white, but some new pipes are unpainted bare copper. When I point the thermometer at the bare copper, or at shiny metal connections (presumably plated brass?), it just reads the ambient room temperature.

Is this as expected? Will I have to paint the copper, and if so, does the colour matter? Any other advice, and am I wasting my time doing this?

[Peter Andrews]

Yes that is normal - try sticking a piece of black sticky tape on the pipe - or masking tape that has been blackened with a felt tip marker pen - and then take a reading. Try pointing it at the sky on a clear dark night as well, it's mighty cold up there :-)

Peter

[John]

You would expect instructions to give this information!

[Alan Braggins]

[...]

The instructions for the Maplin IR thermometer I bought not long ago on special offer did give this information, but I think they've had more than one model, so maybe the original poster's didn't.

[Bill]

No, I've even put my glasses on to read through the instructions again and there is no mention of this. There is a dearer model with two lasers and a third model, I believe. I just got the £19.99 offer one.

I could only find green and fairly shiny insulating tape and that doesn't seem to work. Would a small, say 1/2" blob of black paint work? Presumably it should be matt?

My idea is to work from the boiler to try to track the path the pipes take, so it needs to be fairly consistent, if not accurate.

[BruceB]

Tape is the way forward. Get some black pvs electricians tape, put it on the inlet and outlet of each radiator, and then measuring the temperatures is a doddle.

[John Rumm]

Failing that, just take your reading from painted surface of the rad itself, close to the inlet/outlet. If you are consistent in your choice of location it ought to be adequate for balancing.

[Bill]

Sorry to be banging on about this and to be quoting so much, but am I right to think it's black pvC tape that I need, and presumably a not too shiny variety? The actual balancing should be the second stage. I hope to first monitor the pipes at the boiler, then at the heating and HW valves, then at the input and output side of each radiator. I'm hoping this will give me accurate enough readings to produce a guess at the routing of the pipework, assuming a small temperature drop as the water flows away from the boiler. I've done another google on these thermometers and failed to turn up much new, except one site that did also suggest black paint on the pipes. The white paint on the radiators seems to transmit fine, although perhaps it actually the dust! Tomorrow I'll try to find some sensible black tape though. Shame my multicoloured 12 rolls for £1 (from my "regular supplier" - Poundland) didn't work.

[Dave]

I bought one of these some years ago and I found that the best way to find the temp. drop across a rad was to measure on the input side of the rad, starting from where the water comes in, going up to the top of the rad above this point, just to see where the hottest point is. Point the thermometer at the rad as close to the outlet as you can and you have the temp of the spent heat.

I tried using the pipes as a reference, but gave up in the end. I have to do it all over again now, I've just found out that SWTSMBO has been tinkering with our rads and she has managed to turn off the lock shield valves on some, as she couldn't reach the SOV with enough grip :-(

Dave

[John Rumm]

The material matters more than the colour in this case, and dull surfaces are better than polished ones. The reason is that the thermometer has to make an assumption about the emissivity of the surface it is looking at (although some of the posher ones actually allow you to change this assumed value). The thermometer will probably assume an emissivity in the range 0.95, however a metallic surface will tend to have much lower emissivity than that. Reflective ones can complicate it further since you can see reflected surfaces in them.

If you try an experiment with different types of tape (Insulating, Masking etc) you will find there is little practical difference between the values you will read.

You won't see much drop along a length of pipe - unless it is carrying a very low flow rate.

The emissivity for most non polished organic/painted/oxidized surfaces is close enough to give accurate results regardless. After all you are only interested in relative differences.

Try masking tape. The fact it is not black will make little difference.

[Tim Lamb]

In message , Dave writes

Fit caps which don't engage the valve stem. I have found locking tabs on wall stats useful as well:-)

regards

[Mark]

I've tried masking tape and ther readings I get are all over the place. i.e. it keeps fluctuating by 15C. I don't think the thermometer is faulty since it gives good readings on everything else.

[Andrew Gabriel]

Put the measurement opening close against the tape, and note that the laser aim is completely wrong when close (turn it off, if you can).

[Dave Plowman (News)]

Ordinary PVC tape works fine with mine. But then again it seems to work on bare copper or chrome pipes too. Dunno how accurately, but certainly doesn't read room temperature on hot pipes.

[John Rumm]

Yup, tis what I was going to say - use a wide masking tape or a couple of adjacent strips, and hold the unit an inch or two away from the pipe.

(my one has a scale embossed on the top that shows the size of the sampling area and how it varies with distance; it is approx 1" at 8", rising by another 1" for each additional 8". So to read a pipe and not an average of a pipe and adjoining wall etc, one would need to be no further away than 4", and that is with perfect aim)

[The Medway Handyman]

Mine does that as well. Drives me mad. No idea of how CH & rads work, but can't resist the urge to twiddle.

[Dave]

Mine is the same with remote controls and expects the receiving product to respond instantly :-(

Dave

[Dave Liquorice]

A pet hate of mine is devices that don't respond in some way when I press a remote button. Even flashing a light is enough otherwise you don't know if the command has been received. Without some feedback and a wait of say

5 seconds you press the button again and then the device compounds the problem by queueing it rather than throwing it away as it's busy but hasn't told you. This applies to that bog awful OS Windows, if there isn't an hour glass shown as far as I'm concerned the system is ready for my command but quite a lot of the time it isn't, it may or may not ignore a command so it's even worse by being inconsistent.

[EricP]

Have you ever found them angrily going upstairs carrying a blower fire because the TRV on the bedroom rad does not provide instant heat?