Hot water tank, what about fitting a circulating pump?

[kev123]

Hi all, this is my first post so i hope iyts in the right palce. I have approx 140 Litre copper cylinder fitted with a 31" immersion heater, resettable state and an external stat about third from base. Problem is the top of the tank reaches about 60C but the lower remains very cool, ide guess 20C. The immersion heater state is cutting in and out OK presumably because the top has reached 60C. I understand hot water rises etc etc the cold comes in from the base and pushes the water out etc etc but i was expecting more of the tank to reach 60C any suggestion please? and has anybody ever fitted a small circulating pump to take the water from the top and return to the base of the copper tank to 'mix it up' just a thought ?

 

[Jimbob]

due to stratisfiction the bottom will always be cooler. So is the only source of heat the immersion? if so you saying its controlled by a cylinder stat?

usually the immersion is controlled by an integral stat. So if its too cool it can be turned up in the immersion (on the newer ones anyway)

 

[kev123]

ok i need to explain better. The immersion is the only source of heat, it has an indirect coil but its not convienent to use. It has a new immersion heater, very long at 31" and a the regulatory re settable stat that is turned up to just over 60C id guess 62C ish and thats cutting in and out as you would expect. Ive also an external stat fitted one third up from the base just to be safe but its playing no part in the circuit cos its set to 60C but im guessing that part of the tank is only reacing about 20C. the tank is in the loft ( cold this time of yesr) and is very well lagged with several layers and air gaps so isnt an issue. Any way i can heat more of the tank to 60C how about my suggestion of fitting a small circulating pump to use the hot water from the top of the tank to heat the lower water ? wouldnt increase it above 60C but may give a larger volumn of 60C wwater? ive never seen it before but sounds logical ? or not? thanks

 

[macplumb]

you could try moving the cylinder stat down to the cooler part of the cylinder(just above the cold feed) this will make the stat call for heat untill the lower 3rd reachers temp. The only problem with this is the top of the cylinder will reach a temp over 65'C, this will cause lime build up and a possablity of scolding.
or if all else fails you could change your cylinder for one with a double immersion one at the top as normal and one in the bottom 3rd as a boost which can be ran on a timer.

 

[traineedrip]

i think the moment you draw off water the pump would circulate the unheated replacement water , i doubt youd get a consistant hot supply.

youd also be left with warm water in your cylinder that would take longer to heat .

 

[Bernie2]

There are such things as stratification pumps but they are not usually used on such small cylinder's.

I must admit a 40C difference does seem a lot.

 

[kev123]

you could try moving the cylinder stat down to the cooler part of the cylinder(just above the cold feed) this will make the stat call for heat untill the lower 3rd reachers temp. The only problem with this is the top of the cylinder will reach a temp over 65'C, this will cause lime build up and a possablity of scolding.
or if all else fails you could change your cylinder for one with a double immersion one at the top as normal and one in the bottom 3rd as a boost which can be ran on a timer.

Its not the external stat thats turning off, its the stat fitted in the immersion heater itself because the top of the tank is reaching about 62C the lower external barely reaches 20C

i think the moment you draw off water the pump would circulate the unheated replacement water , i doubt youd get a consistant hot supply.

youd also be left with warm water in your cylinder that would take longer to heat .

Point taken but i was only thinking of running the circulation pump whilst the tank was heating. Once the tank has reached 60C from top to bottom ( or thereaouts) the circulation pump would turn off. When water was drawn it would be taken from the top and replaced with cold in the base as usual.

 

[traineedrip]

Interesting idea