Plumbing – ‘polarity’ of tails.

[Robin GrahamParticipant @robingraham42208]

Obviously a bit off-topic for this forum, but one of the strengths of this place is whatever you ask there is almost always someone who has been there and knows…

A while back I had some plumbing done and asked the guy to take out a couple of radiators and leave tails terminated by isolation valves so I could fit new radiators myself. He's left one tail longer than the the other in both cases, At the time I thought 'Aha! this must be a convention, the current flows from the long tail to the short'. But now I'm ready to plumb in the new radiators I realise that was just an assumption with no rational basis. Just how I would do it!

Does anyone know if there is any such convention and, if so, which way it goes?

Robin

[Robin GrahamParticipant @robingraham42208]

[Mark EasingwoodParticipant @markeasingwood33578]

I ain't no plumber, but starting with cold pipes, ie heating off for a while, the pipe that heats up first should be the flow, and the still cold one the return. If using thermostatic valves on the radiator, most modern ones work on either flow or return. Or try asking the fella that did the job.

Mark

[JasonBModerator @jasonb]

If the pipes are side by side staggering the fittings is usually done to make it easier to do the nuts up and keep the runs the same distance apart

As Said flow will warm up first, if you can't feel it due to being along leg then plumb a temporary loop and open the isolating valves and see which pipe gets hot first.

I would actually say the opposite, it's the modern radiators that tend to be directional particularly designer vertical ones, run of the mill pressed rads can be plumbed either way but watch if using thermostatic valves as a lot of those can be one direction only

Edited By JasonB on 14/03/2021 07:13:11

[SandgrounderParticipant @sandgrounder]

And be aware that if a radiator is removed leaving the lockshield valve and thermostatic valve both shut off and the room goes very cold, the thermostatic valve can then open and drain the system, it happened to me when I left it one night, but if you have isolation valves at both ends you will be OK.

John

[Martin ConnellyParticipant @martinconnelly55370]

Has the mounting wall got limits to where the radiator brackets can be mounted, for example with a stud wall it is best to mount them on the stud (I have seem them mounted to plasterboard and the wall damaged by this). I don't really expect this to be the case as I don't think radiator brackets have a standard mounting layout.

I think the most likely scenario is that he left one short to allow a telescoping connector to be used to make it easy to fit and connect the radiator. Set the radiator up against the long fixed tail, put a telescoping connector into the radiator on the other end and slide it up to the tail and make the connection. Should look reasonably even then and allows for some variation in the width of the radiator. Having removed and replaced radiators without room for telescoping connectors and short vertical tails in the middle of a pipe run I think they are a great idea.

As for them both being on the same side that may just be his own working method. Also one long and one short gives four possibilities for how they are laid out for two radiators and half of the possibilities will be on the same way round so may be just a 50:50 chance and you are seeing more into it than is really there.

Martin C

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Robin, I agree with JasonB that it just makes it easier to get spanners on.

Sandgrounder, I can't say that I've ever seen a thermostatic valve that doesn't have an off position however cold it gets, but most will have a frost setting, which is very often a snow flake symbol.

Regards Nick.

[Brian RutherfordParticipant @brianrutherford79058]

At one time their was a convention to put the flow on the top corner of the radiator and the return on the bottom diagonally opposite. Some thing to do with efficiency and thermal cycling as the cooling water will sink. I think it goes back to large bore pipe work and cast iron rads.

As to the tails being different lengths, the guy didn't bother as he wasn't fitting the rads.

[SamsarandaParticipant @samsaranda]

If removing a rad and leaving a thermostatic rad valve it is best to use the decorating cap, that comes with it, to seal it while the rad is off, the problem is you can never remember where you put it because it was so long ago that you last saw it. I keep mine, have a selection of them because there are different thermostatic rad valves all round the house, in a plastic bag in our cupboard that houses our elec distribution board, only because it is convenient and has space. Also best not to trust lock shield valves as they can leak when rad is removed, learnt the hard way, so have made up a blank Union to screw on the valve outlet to seal it off. Dave W

[SandgrounderParticipant @sandgrounder]

Posted by Nicholas Farr on 14/03/2021 09:33:00:

Sandgrounder, I can't say that I've ever seen a thermostatic valve that doesn't have an off position however cold it gets, but most will have a frost setting, which is very often a snow flake symbol.

Regards Nick.

I'm not exactly sure what caused it but it can happen, turned both valves off in the morning and removed and drained the radiator and everything was dry all day, went to bed and came down to a wet floor with the TRV passing water, luckily the carpet had been taken up, the TRV is still in use and turns off when required but can still pass on very cold days with the radiator getting slightly warm, perhaps it's faulty.

John

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Sandgrounder, it could've just be a build up of scale on the washer or seat, or maybe when you turned off the valve, a small piece of debris got trapped between the washer and the seat.

Regards Nick.

[noel shelleyParticipant @noelshelley55608]

Since we have already digressed I will continue ! Take a piece of copper pipe. Mearure The ID and OD. Find scrap of round steel about 3" or more inches long, with an OD greater than the pipe OD, Put in 3 jaw in the lathe. Machine 2" to OD of pipe measurement. Machine first 3/4" to ID of pipe and taper the next 1/2" to meet OD. Take small hammer(1/2 to 3/4 Lb) Place piece of steel in end of copper pipe, having oiled it and addminister a series of sharp blows.Hold copper pipe in your hand NOT a vice. The copper pipe will be swaged out and you will be able to solder 1 pipe to another with out a fitting. It will be almost invisible. If the fit is sloppy reduce OD a few thou.

FOR THE PURISTS, yes ! I know the swaged wall thickness will be thinner ! but if your up to your anckles in water does it matter ? You've got out of jail – FREE !

I can not claim all honour for this, as Monument used to make a tool like this – but it was the delux version with a built in slide hammer. Mine made over 30 years ago is always in my tool box !! Noel.

[john fletcher 1Participant @johnfletcher1]

My 84 year old wife and I, have changed all our wall mounted radiators (8) during the lock down. Unfortunately the mounting bracket centres were slightly different. Our house will soon be 100years old so no plaster board walls to contend with. We just had one bit of soldering to do, the wife soon got that done. Those extension tails are a good idea and you can get them on sale or return. John

[Steve NeighbourParticipant @steveneighbour43428]

Nuts, solder, swaging, compression fittings ??

All would be alien to a modern 2021 plumber, they pretty much all use push-fit (copper or plastic tube) these days.

Working on a large extension for a family member at the moment and all the central heating and hot/cold water is plastic with push-fit fittings.

Except for gas, that is still soldered copper or threaded steel, but usually hdpe (high density poly ethylene) in the street.

[old martParticipant @oldmart]

In theory, the thermostatic valve should be on the flow side, but it will make very little difference in practice.

[Robin GrahamParticipant @robingraham42208]

OK, thanks. I had hoped against hope that there might be short leg / long leg convention as with LEDs!

The dead legs are too long to feel any difference when the heating is on, so I shall have to plumb in a temporary loop as Jason suggests.

I don't understand why it should matter which end the water goes in, but the installation instructions say:

VERY IMPORTANT:

PLEASE NOTE: WHEN CONNECTING THE PIPE-WORK TO THE RADIATOR, THE WATER MUST ENTER THE RADIATOR AT THE BOTTOM CORNER DIAGONALLY OPPOSITE THE AIR VENT AND EXIT AT THE BOTTOM CORNER BELOW THE AIR VENT.

All those boldface caps and underlining make me fear that HELL WILL BREAK LOOSE  if I get it wrong. It would be good if they explained why it is so VERY IMPORTANT but they don't.

Thanks again for replies, including digressions – always interesting to hear about plumbing experiences!  Plumbing is my most hated DIY house-doing-up task.

Robin

 

Edited By Robin Graham on 15/03/2021 01:05:17

Edited By Robin Graham on 15/03/2021 01:07:08

Edited By Robin Graham on 15/03/2021 01:14:36

Edited By Robin Graham on 15/03/2021 01:19:28

[JasonBModerator @jasonb]

As I said you mostly find the modern "designer" radiators have a specific direction, this is because they have baffles and blocked off passages so that the water is forced to follow a route that will heat all the pipes evenly rather than risk it taking a short cut and leaving cold spots. Even on basic pressed radiator sit is usual to have the entry bottom left as most have the vent top right.

I have done some where you get an insert that is fitted from either side depending on where the flow is but only seen that on the more expensive rads from the likes of Bisque and Zehender but I suppose that's what you get when you spent £1000 on a radiator.

[Grindstone CowboyParticipant @grindstonecowboy]

Posted by old mart on 14/03/2021 15:41:42:

In theory, the thermostatic valve should be on the flow side, but it will make very little difference in practice.

About the only difference would be a bit of a "clunk" noise when the valve shuts if it's on the outlet, as the flow presses the washer onto the seat (on the other end, the flow is obviously trying to push it off the seat, so no "clunk" )

Rob

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Robin, it's quite a few years since I've fitted a new radiator, so it would be best to follow fitting instructions that come with a new one. I have never actually heard or read of the importance of having the vent on the opposite side of the input flow and three out of five of my radiators have the vent on the same side as the input side and I've not had any problems. My central heating was installed about 15 years ago by a professional, but having said that, I found a drawing in a booklet from 1983 from Texas Homecare (remember them) in the scan below.

The only reason I could see about this arrangement for a bog standard or non baffled radiators is that it may reduce the chances of air locks inside the radiators during initial filling. I have never had any problems myself, when for practical reasons for the pipework and access to the air vent, that the inflow has been on the same side below the air vent.

Regards Nick.

[derek hall 1Participant @derekhall1]

On the Danfoss thermostatic valves I have fitted over the last few years, the instructions with the valve show that you have the flexibility to fit them on either flow or return. You configure the valve to do this.

I was always told that it is better to have the control or thermostatic valve on the inlet side, but I have not noticed any difference to be honest as on one or two rads it was more convenient to have the thermostatic valve on the return (outlet) side.

What you need to do though is to find out which pipe is flow and which pipe is return…

Good luck!

Derek

[Martin KyteParticipant @martinkyte99762]

Posted by Nicholas Farr on 15/03/2021 10:20:52:

Hi Robin, it's quite a few years since I've fitted a new radiator, so it would be best to follow fitting instructions that come with a new one. I have never actually heard or read of the importance of having the vent on the opposite side of the input flow and three out of five of my radiators have the vent on the same side as the input side and I've not had any problems. My central heating was installed about 15 years ago by a professional, but having said that, I found a drawing in a booklet from 1983 from Texas Homecare (remember them) in the scan below.

The only reason I could see about this arrangement for a bog standard or non baffled radiators is that it may reduce the chances of air locks inside the radiators during initial filling. I have never had any problems myself, when for practical reasons for the pipework and access to the air vent, that the inflow has been on the same side below the air vent.

Regards Nick.

Unless it's actually stated in text that the vent should be on the opposite side to the feed the drawing really isn't really conclusive unless there is another drawing with the vent on the other side marked up as WRONG. After all if you are going to draw the vent you have to put it on one side or the other. That said the general drift of air bubbles would be from the flow side upwards towards the return side however as the vents are not actually at the top of the header there is always going to be some air in the system so I think people are reading too much into the drawing.

We do take drawings as gospel especially when we are unsure of the designers thinking (I'm not just talking about radiators here) when there are often no real reasons why we should not do it differently, changing threads comes to mind when specified taps are not available is one such instance.

More important to have the valve where it will a. Fit and b. Be accessable.

regards Martin

[jon hill 3Participant @jonhill3]

Hi Robin

The different pipe length is purely coincidental, what you will probably find is the pipes underneath the floor are loosly clamped to allow movement to the desired height. Nothing to worry about both flow and return pipe should be loose to make life easier to fit. As to which is the flow and return if you still have the old rad could you re-install and check which gets hot first or as others have said bridge the 2 pipes. For the later solution you may have to drain down thus wasting the inhibitor (fernox et al) to rig-up a temporary bridge.

Jon

[Dave HalfordParticipant @davehalford22513]

If you're tight and the inhibitor is not that old and it's not a Combi you can turn off all the rads and drain down into a bucket (three actually) finish the job then go pour it back in the header tank.

[Grindstone CowboyParticipant @grindstonecowboy]

Bleed valve should be as indicated in the diagram because, if the rad is hung perfectly level, the flow will tend to drag any air towards it.

Rob

[old martParticipant @oldmart]

Back in the early 70's when I was fitting central heating, the preferred flow was in at the bottom and out at the diagonally opposite top for the best heat output. That rarely happened in practice.

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