Install radiator pipes top/bottom or both at bottom?

[phil090207]

Firstly apologies for asking a FAQ, but there are contradictory answers in various threads on this forum so I'm a bit confused. I've read several guides to installing radiators and none of them answer this.

Is there any benefit to putting one of the radiator pipes at the top of the radiator as opposed to both at the bottom? All the existing rads in my house are connected at top and bottom with the TRV at the top. Why? Do they heat up faster? Get hotter? Get less trapped air? Make less noise? Is it to get the TRV higher in the room? To provide a drain point at spare bottom hole?

If there's any point in doing this, is the top pipe the in pipe or the out pipe? And which one should the TRV go on?

Many thanks for some advice.

 

[kevplumb]

TBOE

top bottom opposite end is the way rads are connected to test the heat output

i think it's a little higher

or you may have a one pipe system

 

[D_Hailsham]

Is there any benefit to putting one of the radiator pipes at the top of the radiator as opposed to both at the bottom?

In theory a rad with the flow connected to the top and the return at the bottom will give off about 2% more heat than one with both connections at the bottom.

which one should the TRV go on?

Provided the TRV is designed to go on either end (two arrows at right angles on the body) it does not matter. Though there might be a slight advantage in having the TRV at the top where it is easier to get to and nearer head level. It is always better to have the TRV horizontal, if possible, as the rising warm air then flows over the sensor.

 

[advancedplumber]

there r only 2 reasons for top and bottom entry radiators. 1 as already pointed out, for an old 1 pipe system, or 2 for a gravity system. i would put back in the way it was b4.

 

[bengasman]

Connecting the flow at the top, and the return at the bottom was the way it was done with gravity systems, which were popular in the 19th century with the happy few who could afford them.

In the mid 20th century when pumps became popular, those who liked traditional ways, stuck with the way valves had always been installed, often leaving a heap of corrosion debris (crud, mud, gunge) in the rad under the high valve. (this gave birth to the expression: "stick in the mud")

In today's heating technology with fully modulating systems, this way of doing things has become completely obsolete.

Possibly exceptions may apply to grade 1 listed buildings, but that has nothing to do with technical reasons.

 

[bengasman]

In theory a rad with the flow connected to the top and the return at the bottom will give off about 2% more heat than one with both connections at the bottom.

Interesting, never heard that before.
Seems to contradict logic. Flow in low, will heat that side from top to bottom.
Flow in high, and the bottom corner will never be that warm.
Any documentation on line that explains how this works?
Before anyone jumps on this, I know a theoretical 2% is not measurable or interesting from an economical or technical point of view.
I am just curious.

 

[phil090207]

Wow that's loads of information, thanks very much everybody.

Its definitely not a gravity or one-pipe system, its a pumped system with standard plumbing and the rad I'm installing is a modern one.

Yes the TRV is reversible. I've just read the TRV instructions, it says if installing at the top, always mount horizontally, but if at the bottom it can be vertical or horizontal. I guess the idea is to keep it in the room temp air stream rather than the hot stream coming off the radiator??

Because space is a bit tight, I want to mount the TRV vertically, so if only for this reason, I will go for both pipes at the bottom.

Many thanks again for all the advice.

 

[kevindgas]

you have raised another issue with the TRV comment as UK is one of the few countries where TRV's are fitted Vertically
a horizontal fit is less sensitive to latent heat from pipework and is apparently more acurate in temperature sensing.

 

[kirkgas]

used to fit heating for old eaga contract and we were told to fit TRV's at high level for ease of use by customer, seems fair enough, (it was about the only feckin useful thing about the whole contract)

 

[doitall]

Still done TBOE when using steel pipe, it's better for connecting the bottom pipe. 90% m&f bend, a 45% m&f bend and a short length of pipe into the valve.

Hardly ever done with copper because it would be to vulnerable to gwetting damaged.

 

[D_Hailsham]

In theory a rad with the flow connected to the top and the return at the bottom will give off about 2% more heat than one with both connections at the bottom.

Interesting, never heard that before.

I am just curious.

For example, see: http://www.plumbingpages.com/featurepages/CorrectionFactors.cfm

 

[bengasman]

Cheers geez.

Reading through that, I noticed a couple of things.
Apart from the odd 2%, the MWT for steamers would be 15 k lower than the 90-70 used here. At an average of 2% per K, that would lower the advertised output using the old standard by about 30%.
Makes calculating to the watt accurate (let alone btu) a bit of a joke.

 

[doitall]

I don't know who wrote that rubbish DH but TBSE is having a laugh, unless there's no alternative.

If you draw a curve from the top corner opposite the connection too about half way along the bottom of the rad and shade it in that will be the cold spot and sludge collector.

 

[kevplumb]

err you use a tube in the bottom valve 2/3 the lengh of the rad same as twin entry

 

[doitall]

err you use a tube in the bottom valve 2/3 the lengh of the rad same as twin entry

That would make it worse, even if you could insert a tube, a feat I would guess is impossible in 70% of all rads.