horizontal hot water cylinder - can't be right

[waysidetim]

Our house is on economy7 and we used to have a 210l hot tank gravity fed from the loft, which supplied us with two hot baths a day plus washing up water. We have recently installed a new shower so had to move the hot water tank into the loft. Because of restricted height we installed a Telford horizontal unvented direct horizontal cylinder with 300l capacity. This feeds only the bath and hot water taps, not the shower.
Having tried it for a week I am really shocked by the lousy supply. The tank is set to 60C and gives piping hot water. Run a bath of approx 120l and wait 15mins - when I come to top up the bath the water is tepid. So far our 300l tank gives us one small bath of piping hot water, everything else is luke warm.
I understand the science and that the outflow is topped up with cold mains. In the old vertical cylinder mixing was more limited (and at less pressure) but even so this is ridiculous.

We can of course use the boost facility to reheat the tank after a bath but this is using peak electricity and defeats the object of the exercise. The system was installed as suitable for economy7 use and the whole point is not to use the boost at £0.22p/unit but heat water overnight at £0.05p/unit The tank was ferociously expensive (over £1300) and as value for money is clearly dreadful

Can anyone enlighten me? Is this system simply unsuitable for econ7 or is there a problem with the tank? The electrician confirms its receiving both night rate feed and separate boost on demand

 

[htgeng]

Can anyone enlighten me? Is this system simply unsuitable for econ7 or is there a problem with the tank? The electrician confirms its receiving both night rate feed and separate boost on demand

horizontal cylinders are a complete waste of space, essentially because you have very poor stratification due to the height of the cylinder. Add to that problem, I bet there is little or no baffle on the cold water inlet so the whole tank is being sloshed around giving you the 'tepid' results.

I think you will have to live with it or tbh you would have been better off putting a 210 unvented tank where your old one was! Can you turn the cylinder upright and sit it anywhere?

 

[waysidetim]

thanks for the reply. there is now a shower where the old tank was, hence had to move the hot water system into the loft. Its a pretty depressing (and expensive) exercise so far, and the loft space doenst have enough height for a reasonable sized vertical cylinder. I did think that having a long horizointal system with cold water coming in under pressure would result in excessive mixing of hot/cold and hence cooling. I suppose i just assumed someone must have thought of this and taken steps in the design to minimise this. Doesnt seem to be the case, and as a suitable system for economy7 it really is awful

 

[Softus]

I really feel for you, waysidetim. It's an expensive mistake to have made.

I know nothing about horizontal cylinders, but be aware that you might have a valid claim against the installer or manufacturer on grounds of fitness-for-purpose (i.e. lack of it).

 

[philtheplumber]

I know this post is ancient but if a secondary return pump is fitted from hot out to cold inlet and set to come on as the immersions then the whole tank is heated the same. You do not get good stratification on heating such an area of water on a horizontal as it is wide and short.

 

[snb]

it could be possible that the installer has fitted the cylinder 90 degrees out. This could cause the econ immersion to only heat half the tank