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Gravity fed radiator


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Hi guys, im looking to 'finally' plumb in one radiator off my diesel stove,

 

the diesel stove has the built in jacket, and sits fairly central in boat.

 

All looks like it should work,

My questions are if the stove outlet is 15mm and a new rad comes with 15mm, will 28mm pipe really make any difference to flow?

 

Also coming out the top of stove it needs to run behind sink etc, 

should the pipe work be done with one pipe, nicely bent, or can I do straight cuts, out then up 90, across 90, down under gunnel straight, then drop down 90 to rad, return pipe would be lower anyway, running back skirting board height?

 

Chers,

 

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I am not going to comment on the 28mm pipe because the stove outlet seems to be 15mm, rather than 1" BSP but use bends rater than elbows for al the 90 degree bends.

 

I am also not too clear on  how you intend to connect the rad. On a gravity system I would expect the got inlet to be at the top in the position the bleed screw can be fitted.

 

As its an oil stove so ca be turned off within seconds and it has a temperature control a circulating pump has far fewer dangers than on a solid fuel stove  if gravity circulation does not work as hoped.

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crude image hear of pipe work I was suggesting...

 

 

 

18 minutes ago, Tony Brooks said:

I am not going to comment on the 28mm pipe because the stove outlet seems to be 15mm, rather than 1" BSP but use bends rater than elbows for al the 90 degree bends.

 

I am also not too clear on  how you intend to connect the rad. On a gravity system I would expect the got inlet to be at the top in the position the bleed screw can be fitted.

 

As its an oil stove so ca be turned off within seconds and it has a temperature control a circulating pump has far fewer dangers than on a solid fuel stove  if gravity circulation does not work as hoped.

 

Thanks Tony, for bends do you mean pipe bend them, or do you mean those soldered bends...

 

also for the flow of the pipe what do you think, if its generally higher, and falling is that ok,

 

rather than some diagrams show a pipe going gradually up at an angle to feed the first rad, is that necessary?

 

Its the same on the cold return, can that have an angle up and into the diesel stove, as that pipe would still be lower than the hot feed?

 

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Edited by John Lewis
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I was talking about solder, push fit or compression fittings, whichever you will find easier. The important thing is an elbow so almost a right angle but a bend, while still turning the pipe run through 90 degrees is longer and deeper so it is a much gentler 90 degrees that causes less restriction to flow.

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40 minutes ago, John Lewis said:

My questions are if the stove outlet is 15mm and a new rad comes with 15mm, will 28mm pipe really make any difference to flow?

 

Yes.  It's the ratio of area to circumference of the tube that affects how much drag there is on a fluid.  This is more significant on a thermosyphon system than on a pumped system.

 

That said, 28mm is probably overkill for a single radiator, but 22mm will certainly work better than 15mm tube.

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A 60' hire boat we used in the late 1970s had gravity-fed radiators heated via a gas boiler. As far as I recall, it  managed with 22m pipes. Agreed about the slow bends and no sharp right angled bends. Large radius bends for copper pipes  seem to be unobtainium in my local builders' merchants now, so you might need to bend pipe yourself. Burrs at the cut ends of pipes should be carefully removed. A gentle  progressive gradient should ideally be provided in the flow and return pipes, and dead horizontal runs avoided where possible. 

 

When I designed the central heating system for my own house in the power-cut era of the 1970's, I designed it with gravity circulation in mind so it would be operable (at lower performance) in the absence of mains electricity. At that  time there were DIY books available that had information on designing both gravity and pumped systems.  22mm copper worked ok. A lot of the older books discussing gravity systems had flow resistance figures based on iron pipes which, due to their rough interior surfaces, have a higher flow resistance than a copper pipe of the same bore. 

Edited by Ronaldo47
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9 minutes ago, Tony Brooks said:

I was talking about solder, push fit or compression fittings, whichever you will find easier. The important thing is an elbow so almost a right angle but a bend, while still turning the pipe run through 90 degrees is longer and deeper so it is a much gentler 90 degrees that causes less restriction to flow.

 

Thanks Tony, but Im not really following you - " use bends rather than elbows"....

 

basically are you thinking a couple of compression fittings is ok, rather than one continuous pipe?

 

 

2 minutes ago, Ronaldo47 said:

A 60' hire boat we used in the late 1970s had gravity-fed radiators heated via a gas boiler. As far as I recall, it  managed with 22m pipes. Agreed about the slow bends and no sharp right angled bends. Large radius bends for copper pipes  seem to be unobtainium in locsl builders' merchants now, so you would need to bend pipe yourself. Burrs at the cut ends of pipes should be carefully removed. A gentle  progressive gradient should ideally be provided in the flow and return pipes, and dead horizontal runs avoided where possible. 

 

When I designed the central heating system for my own house in the power-cut era of the 1970's, I designed it with gravity circulation in mind so it would be operable (at lower performance) in the absence of mains electricity. At that  time there were DIY books available that had information on designing both gravity and pumped systems.  22mm copper worked ok. A lot of the older books discussing gravity systems had flow resistance figures based on iron pipes which, due to their rough interior surfaces, have a higher flow resistance than a copper pipe of the same bore. 

I see what you mean Ronaldo, a gradual rise in the pipe probably allows heat to circulate up better..

 

Its just that theres a nice gap above sink where an existing hole was cut (see image above) , was thinking the difference would be negligible if I went straight across there...?

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1 minute ago, John Lewis said:

 

Thanks Tony, but Im not really following you - " use bends rather than elbows"....

 

basically are you thinking a couple of compression fittings is ok, rather than one continuous pipe?

 

 

 

Yes, pipe fittings, because I know that without a pipe bender it needs skill to bend 22 mm pipe through 90 degrees, let alone 28mm.

Ideally you would make the bends yourself so you cam make them even larger than fittings allow but for most  it is simply not practical.

 

 

 

 

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2 minutes ago, Ronaldo47 said:

Agreed about the slow bends and no sharp right angled bends. Large radius bends for copper pipes  seem to be unobtainium in locsl builders' merchants now, so you would need to bend pipe yourself.

 

I cheated on my own boat, using two 45 degree elbows to make a softer 90 degree bend.  Gently bending 28mm tube so it fits correctly isn't for amateurs!

 

This also meant I could rotate in two planes to make a good fit between the backboiler fittings, rising up the flare on the hull and tucking neatly under the gunwale.

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3 minutes ago, John Lewis said:

"Needs skill..... not for amateurs...." I think I know what I need to do!

 

last question: for the header tank - do I just tee off from a compression fitting before rad...

 

 

Thanks all.

 

Personally I would T it into the highest point in the system so it vents air more easily.

Just now, David Mack said:

 

Have you tried to use one at 22mm and was successful every time? I can do 15mm with one but find 22mm ande above difficult and often kink the pipe and get the spring stuck.

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How far from boiler to rad? If its less than 4m to 5m then 15mm will be fine if it is installed well. If not, then 22mm for the straight run on the flow and return with 15mm on the verticals to the boiler. If 15mm try to avoid any soldered bends, its easy to bend with a spring.

Can you guarantee that the flow from the boiler is rising all the way to the highest point even when the trim of the boat changes? And the return rises all the way back to the boiler so it vents

Can you join the header tank feed to the absolute highest point? 15mm will be fine for the feed/vent.

Use a bending spring wherever possible. Slow copper bends otherwise.

Plastic pipe is out unless you fasten it on top of a continuous batten to avoid sags and crests which will make venting air impossible.

Flow into top of rad, return opposite bottom is best for flow and heat output.

 

Anything else, just ask.

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7 minutes ago, John Lewis said:

Not always but they often squeeze the pipe either side of the bend. A spring is better but you have to use it carefully on soft or annealed pipe section, not thin wall copper. 

Don't just pull a spring out, relax the bend slightly and twist the spring up as you pull.

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When copper pipe is made, it is drawn through a die.  That means it is already somewhat work hardened, and  does not want to be bent,  so the other trick with bending the bigger sizes on a spring is to re-anneal the pipe at the bend site before you start.  You only need to get it very hot with a big gas blowlamp.  You can cool it in water if you are in a rush, or just wait. Then you can do 28 mm across your knee.

 

Annealing also makes it easier with the Rothenberger type benders, and eliminates the wrinkly bits on the inside of the bend.

N

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14 minutes ago, BEngo said:

When copper pipe is made, it is drawn through a die.  That means it is already somewhat work hardened, and  does not want to be bent,  so the other trick with bending the bigger sizes on a spring is to re-anneal the pipe at the bend site before you start.  You only need to get it very hot with a big gas blowlamp.  You can cool it in water if you are in a rush, or just wait. Then you can do 28 mm across your knee.

 

Annealing also makes it easier with the Rothenberger type benders, and eliminates the wrinkly bits on the inside of the bend.

N

Your knees will be bigger and harder than mine if you can bend  even annealed 28mm on them!

I stop at 22mm on my dainty knees.

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You need to bear in mind that there are (or at any rate, used to be the last time I needed any) three different grades of copper pipe: Hard; Half-hard, and Fully Annealed.  Tables X, Y and Z, but not in that order! The Hard grade has thinner walls (and thus a larger internal diameter), but is not bendable. It is/was cheaper than the half-hard, which is bendable with springs and bending machines. The fully annealed stuff has thicker walls still and is readily bendable by hand and was/is mainly used for cold water mains underground, but I guess has now largely been replaced by plastic. The thin wall stuff used to be significantly cheaper as it contained less copper. I did manage to put  gentle bends in two lengths  of 28mm thin wall (non-bendable)  pipe that I needed for the gravity feed from my gas back boiler to my hot water tank by using a home-made bending block of the type that that old books described as being used by builders for bending pipes in the days when proper pipe benders were expensive. Just a hole somewhat  bigger than the pipe, drilled  through a piece of fairly thick  timber. You secure the wood to something immovable,  thread the pipe through the hole, leaving enough out to get a good leverage, and press down firmly. The pipe will bend slightly where it emerges. Pull out the pipe a bit more and repeat. Or perhaps it was push the bent bit through the hole and repeat, it was a long time ago when I last did it. I managed to make enough gentle  step-wise bends with some slight crippling of the pipes  that was sufficient for my needs and I did use a blow lamp first to soften the pipe at the bend location. The pipes were at the back of a built-in cupboard so appearance was unimportant.  

 

 

 

Edited by Ronaldo47
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I remember my father fitting central heating when I about 7 or 8 years old. Must have been gravity hot water as he was using 28mm (or probably 1 1/4 in) pipe. He had bought just enough pipe, but one piece had got bent slightly and started to flatten. Rather than buy another piece of pipe I remember him putting a 3/4 in bending spring in and bending it some more to the desired shape. What I don't recall is how he got the spring out again!

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