Will top coil heat whole cylinder ?

Hi,
Does anyone know if heat going to top coil of a dual coil cylinder will heat the all the water in a cylinder. I am installing solar and have dual coil 300 litre cylinder with solar driving bottom coil and central heating driving upper coil. In times when there is a little solar energy (lots of the time will the upper coil be able to heat the entire cylinder or will the upper part only be heated ?
Thanks
ennisjim

Afraid not. Water is a poor conductor of heat, so the upper coil won't effectively heat the entire tank.
Leo

Hi,

Just to supply a little bit more info - probably doesn't make any difference.... The top coil is from a solid fuel stove back boiler. We have a good supply of solid fuel so the stove/back boiler will be active quite a bit (also supplies space heating into a largish space) so I was wondering if the fact there is a plentiful supply of hot water from back boiler would mean that the lower part of tank would also heat up eventually (ie. in a reasonable period of time, eg. hour or two) ?

Thanks
ennisjim

Hi EnnisJim,

Heat rises, therefore it is very unlikely that the top coil will heat water in the bottom of the tank.


ALERT.

That's true alert, so would it be true to say then that as we continue to burn fuel in the solid fuel stove it's more likely that boiling water will be vented from system than cold water at bottom of tank will be heated ?

it's more likely that boiling water will be vented from system than cold water at bottom of tank will be heated ?

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As mentioned above, heat rises. However there are other factors to consider such as Brownian motion and the metal of the cylindar heating up.

The bottom will eventually heat up, but not too efficiently.

ennisjim said:

That's true alert, so would it be true to say then that as we continue to burn fuel in the solid fuel stove it's more likely that boiling water will be vented from system than cold water at bottom of tank will be heated ?

Click to expand...

You really must add in an additional heat leak somewhere especially since you are going to have solar as well. Boiling water in your tank is never good from a safety point of view plus brushing your teeth with warm water pitched over in a cold water storage tank is never nice.

A simple two port normally closed valve triggered by an anti boil stat to divert the heating circuit off to a second small un-insulated hot water cylinder (which would be the cold feed for your main hot water cylinder) would do the trick. You solar should stop circulating when cylinder reaches a set temperature.

Take this for example I have a 220 ltr copper cylinder with factory fitted insulation. If I run my oil boiler at 75 degrees and heat full tank, I will have approx 50-degree water 24 to 36 hours later. Stainless steel cylinders hold their heat even better.