Magnetic Radiators

Quite by chance I noticed that a compass sitting on a table next to a central heating radiator was not pointing to North. Moving it to the middle of the room it corrected itself. Checking the needle at each end of the radiator, there was a North and South polarity through the length of the rad.

Tried this around the house on several other rads with the same result.

Gas fired central heating boiler . There is a magnetic filter in the system which was recently cleaned during annual service.

Have any of you chaps got an answer to this phenomenon?

Mike

Edited By Watford on 23/03/2018 09:19:39

hi Mike if your radiators are old it could be rust particles going round the system maybe small ones getting past the mag filter a magnet used to stick on the copper pipes on my system before we renewed it due to the rust particles in the water

Dave

I believe that any large, static lump of iron will, over time, pick up enough of the earth's magnetic field to turn itself into a (weak) magnet. So I don't think it's anything to do with the magnetic filter. A solution would be to rotate your radiators on a regular basis

I have read that ships gain their own magnetic field whist being built, the effect varying with the orientation of the slipway - that's why compasses have compensating magnets.

Regards,

Rob

Mike,

I expect that the yachtsmen will be along soon, to explain properly ... but in the meantime, I think you have probably been misled by your observations:

The compass compensation is, I believe, being disturbed by the presence of the radiator and its general location as an entity, rather than its magnetic polarity end-for-end.

MichaelG.

The steel of the radiator would completely shield any field from particles in the water. It's more likely that any residual field was created during the manufacture of the radiators in the factory. Possibly due to the resistance welding process (very high currents) I assume is used to join the seams?

Many battleships used to have vast degaussing cables around them, for demagnetising the entire ship to reduce their likelihood of triggering magnetic mines etc. The currents and number of turns used must have been pretty large!

Murray

I'm not at all surprised - radiators are made of pressed steel which is magnetic. Large bits of steel seem to get weakly magnetised quite easily - for example when they are made they probably get very hot, then cool down in the earth's field, which will freeze in a small remanent field. They do seem to be magnetised if you're seeing a difference in deflection at each end.

You will clearly have to carefully compensate your compass for the room in which you normally do your navigation. Alternatively I can recommend GPS, or if you use a south-facing conservatory perhaps a sextant combined with stellar observations.

The radiator doesn't have to be magnetised at all in order to have an effect on the compass. For example, aircraft regularly have to have their magnetic compasses "swung" and the results logged on a correction chart held in the aircraft to compensate for errors caused by the electronics and ferrous and other metals in the airframe. This is carried out in a designated area on an airfield which has been inspected, approved and marked for swinging the compass. Not surprisingly it's called a "compass swing bay"! I imagine other forms of surface transport utilising a magnetic compass have a similar system.

John

Thanks J.H., I am going with the sextant option!!!

Thanks also to all others who contributed. I am concluding that the cause is probably the residual magnetism from manufacturing heat and pressing. The boiler and radiators are only two years old and the system was well flushed at the time of change, so I think it unlikely that residual sludge is the cause. BUT you never know! Anyway your responses have answered the question, and for this I am grateful.

Mike

Not quite the same, but my workshop vice has turned itself into a horseshoe magnet....

Martin

That would be a horseshoe for a Trojan horse, would it Martin?

Mike

Surely a steel radiator will attract the magnet. I remember when I was in the army being shown how to read maps and compasses The compasses were deflected by the ironwork under the tressel tables we were working on

Roy

A simple compass could be used to analyse this. If every radiator, end of radiator has the same attraction to the compass needle then it's just the fact of a lump of iron. If the radiator ends are all Nth or Sth [poles then it occurred in the factory. if the rads Nth and Sth poles relate to their orientation in the house then it happened post installation due to earth's field and some vibration from circulation,. air bubbles, etc.

If it is random and comes and goes month by month then check the skies for UFO's

pgk

Placing a compass close to any, iron structure will cause the compass to deflect from magnetic north. In a previous life I have been known to get students to investigate magnetic fields when working close to the structural ironwork of the lab .

Brian C

Posted in error. Nick

Edited By Nick Thorpe on 24/03/2018 19:51:06

Even if the radiator is not itself magnetised, its magnetic permiability will create a local distortion in the earth's magnetic field, which will depend on the angle of the radiator to the earth's field.

I suggest that for a true reading, you take your compass a significant distance from the radiator (say > 5 radiator lengths?) in order to minimise the field distortion caused by the radiator.

Martin

(edited for spelling)

Edited By Martin Whittle on 24/03/2018 20:01:23

.

Martin,

I suspect that Mike has effectively demonstrated this already.

MichaelG.

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Posted by Watford on 23/03/2018 09:18:39:

Quite by chance I noticed that a compass sitting on a table next to a central heating radiator was not pointing to North. Moving it to the middle of the room it corrected itself.

Edited By Michael Gilligan on 24/03/2018 20:08:54

Micheal

I was telling him why

Martin

Michael

I was telling him why.  And specifically, that it is not necessary for a radiator to be magnetised in order to distort the local magnetic field.

Martin

(sorry - another spelling error!)

Edited By Martin Whittle on 24/03/2018 20:17:24

No doubt radiators are welded up in a jig, which would explain them all having a field of the same polarity.

.

No offence intended, Martin

... I was trying to emphasise your point.

MichaelG.