cast rads , flow or return?

[that bloke.]

you know the way cast rads have the inlet and outlet at different ends staggered? what goes to the top and what goes to the bottom?
is it the flow that enters at the top of the rad?

 

[Puddle]

Yes flow in at top ,return out bottom,the same as a cylinder,as water cools it falls,however in these days of fully pumped systems, not so important but still good practice

 

[WHPES]

it is recommended to configure larger cast rads this way to obtain optimum efficiency, whether pumped or not. It isn't important for steel rads as they don't contain anywhere near as much water.

 

[that bloke.]

lovely , thank you gents.

 

[doitmyself]

Yes flow in at top ,return out bottom,the same as a cylinder,as water cools it falls,however in these days of fully pumped systems, not so important but still good practice

Some say that the flow should go in the bottom of the cylinder and return out of the top.

 

[WHPES]

Because of stratification (hottest water at the top) you want the hot water from the boiler to come in at the top of the cylinder and out of the bottom. That way you will always get some hot water.

Take the following scenario - hot water comes in at the bottom of the cylinder coil and the cylinder is tepid. The water nearest the bottom of the coil heats up and rises up the cylinder. In the process it meets cooler water and mixes, thus ending up with a lower mean temperature higher up. Therefore with hot water going in at the bottom, you have about 1/3 more of the water in the cylinder to heat up in order to get the same hot temperature of water coming out of the taps.

 

[doitmyself]

So with the standard connection (flow above return) only the top 2/3 of the cylinder is full of usable hot water.

I can't lay my hands on the document recommending flow in at the bottom, but the OSO cylinder installation instructions all show flow at the bottom and return at the top.

 

[gakmonkey]

I seem to remember the telford unvented cylinders having flow at the bottom return at the top for quicker recovery.