Hot water cylinder losing heat

[JonBodge]

Hi! My first post here.

I have a vented hot water tank, it's one of these - Gledhill SE26X18IND - it appears to be good quality. It is heated by an oil boiler with central heating in a Y system configuration. The pump, zone valve and timer / controller are new. After running the HW heating in the morning, the water in the tank is very hot, but by the evening it's lost a lot of heat. We have a 2 bar power shower and I use it each morning, not for excessive periods, and I can tell the water is still really hot when I get out. So, it seems to me I am losing heat from the tank during the day. The tank is insulated with foam ("EnviroFoam" they call it).

What can I do to reduce heat loss in the tank? I have yet to insulate all the pipework - could this be the cause?

Sorry. I know these sound like stupid questions. I realise heat will be lost from the top of the tank and the pipe coming out of it, but surely not that much so as to be noticeable over 10 hours. It's obvious that I can improve the tank insulation, but do I need to? I suppose what I'm asking is "Is there anything else that might cause this?"

 

[cross thread]

Dripping hot tap can / leak ?

 

[JonBodge]

No leaks, but good thought.

 

[Murdochcat]

During the winter the hot water you are using means the "top up" is colder water, which has a cooling effect on the remainder of the hot water.

See what happens over the next few weeks as the ambient temperature rises

 

[JonBodge]

Now that's a good point I hadn't considered. I have insulated the header tank, though, but it's 1" thick Kingspan only.

Doesn't the hot water convect to (and stay at) the top of the tank, though? The refill pipe's at the bottom - how easily does it mix with the hot water?

 

[Harry Bloomfield]

If you use HW from the cylinder, then that has to be replaced from the cold tank in the loft. Due to stratification, the HW will remain at the upper part of the cylinder, but even so, it will suffer some mixing as the cold flows in. Your best way to be sure whether the heat is being lost, is to bring the cylinder up to temperature, then not use any - see how long it then holds the heat.

 

[ChrisJP]

You could also put extra insulation onto the tank - the applied foam on new tanks is good, but in my experience doesn't insulate all that well. I haven't seen them for a while but you used to be able to get insulation jackets that are designed to fit the old uninsulated copper cylinders. If you can get one, this would be worthwhile putting on top of the existing insulation

 

[Harry Bloomfield]

You could also put extra insulation onto the tank - the applied foam on new tanks is good, but in my experience doesn't insulate all that well. I haven't seen them for a while but you used to be able to get insulation jackets that are designed to fit the old uninsulated copper cylinders. If you can get one, this would be worthwhile putting on top of the existing insulation

Some while back, by way of an experiment, to what difference it would make, I repurposed an old bed quilt put over my cylinder. I simply threw it over, and tucked it loosely into place, as best I could. It made a quite surprising difference, to how long the HW temperature was retained, if not used. I have the HW heating (60C) go off at 20:00 each day. The (unused) HW was still too hot to stick your hand under the tap, by mid-morning next day.

 

[Johntheo5]

Hi! My first post here.

I have a vented hot water tank, it's one of these - Gledhill SE26X18IND - it appears to be good quality. It is heated by an oil boiler with central heating in a Y system configuration. The pump, zone valve and timer / controller are new. After running the HW heating in the morning, the water in the tank is very hot, but by the evening it's lost a lot of heat. We have a 2 bar power shower and I use it each morning, not for excessive periods, and I can tell the water is still really hot when I get out. So, it seems to me I am losing heat from the tank during the day. The tank is insulated with foam ("EnviroFoam" they call it).

What can I do to reduce heat loss in the tank? I have yet to insulate all the pipework - could this be the cause?

Sorry. I know these sound like stupid questions. I realise heat will be lost from the top of the tank and the pipe coming out of it, but surely not that much so as to be noticeable over 10 hours. It's obvious that I can improve the tank insulation, but do I need to? I suppose what I'm asking is "Is there anything else that might cause this?"

If this is a 117L capacity cylinder?, if just you have a 12min, 15LPM shower at 60C then you will have used ~108L at 60C leaving around 9L, this will still be quite hot when you finish but won't take long to cool down even if it is on top of the cylinder, except you are reheating the cylinder after the shower?.

 

[pcaouolte]

if just you have a 12min, 15LPM shower at 60C then you will have ...

... a trip to hospital. Showering at 60C would cause scalding.

 

[Johntheo5]

A typo I hope, that 108L at 60C mixed with 72L at say 10C will give 180L at 40C, enough for a 12 min shower at 15LPM.

 

[Johntheo5]

Losing excessive heat overnight can also occur if the mid position valve's last port of call was HW heating which can cause gravity circulation through the heating coil, a spring loaded NRV just before the coil inlet should stop this.

 

[Harry Bloomfield]

Losing excessive heat overnight can also occur if the mid position valve's last port of call was HW heating which can cause gravity circulation through the heating coil, a spring loaded NRV just before the coil inlet should stop this.

Yes, my system does have that isssue (MOMO 3-port valve), but the heating comes on last thing on an evening, which to some extent prevents it.

 

[ChrisJP]

I can see that the tank is insulated with 35mm thickness of spray foam insulation. This really isn't all that thick, and adding more insulation over it with definitely improve heat retention.

 

[Johntheo5]

Yes, my system does have that isssue (MOMO 3-port valve), but the heating comes on last thing on an evening, which to some extent prevents it.

This was noticed by someone who had been doing the same as you, heating on last at night to reduce it (by a very substantial amount) but then installed the NRV and modified the Y plan so that the valve is powered only when both CH & HW requested or CH only so allways returns to HW at night.