Ho wlong does hot water stay at max temp (within 4 degrees) in a boiler?

[boilerboy22]

Hi,
In a typical household hot water boiler, how long does the water stay at max temperature with no more electrical energy going into it?
Please state this for different boiler sizes?
Assume properly lagged etc.

 

[oz-plumber]

Probably never.
The boiler is set up with a pump over run to reduce the temperature of water in the boiler after the gas valve shuts off.

Most boiler are set to 3 minutes pump over run - but can be altered down to 1 minute if you deem it necessary.

 

[ShaunCorbs]

Around an hour maximum before it kicks in again for pre heat

 

[boilerboy22]

Thanks, but sorry i dont understand. After the boiler water has got to max temp, the cold water valve is opened to cool the water back down again?
What if theres no more room for any more water to go into the boiler?......say its at night time, and nobody is using hot water?

 

[boilerboy22]

Around an hour maximum before it kicks in again for pre heat

Thanks, do you not what temperature drop that is that brings the heating element back on again....?

 

[ShaunCorbs]

Around 10-15dc so 45-50dc

 

[exedon2]

Reading your question do you mean heating boiler or hot water cylinder?

 

[boilerboy22]

..thanks, i am speaking of the main boiler of the house, the one that provides water for the bath, shower, and presumbaly the central heating.
Sorry I am not familiar with the term "hot ater cyliner".

If you have heard of the Eddi hot water heater, then its the boiler that gets supplied by that.

 

[ShaunCorbs]

Reading your question do you mean heating boiler or hot water cylinder?

Cylinder

 

[Chuck]

Hi,
In a typical household hot water boiler, how long does the water stay at max temperature with no more electrical energy going into it?
Please state this for different boiler sizes?
Assume properly lagged etc.

Is this a homework problem by any chance?

A typical modern domestic hot water storage cylinder contains 170 litre of water and loses ca 50W. This corresponds to an average rate of cooling of about

50 [W] / ( 170 [kg] * 4200 [J / °C kg] ) * 3600 [s / hr] = 0.25 °C / hr

A small (70 litre) cylinder of the same type will cool faster, say 0.45 °C / hr, and a large (300 litre) cylinder will cooler slower, say 0.20 °C / hr.

Note that I said 'average' because I've not included the impact of stratification, which would increase the rate of cooling at the top and decrease it at the bottom.

 

[John.g]

Came across this some years ago so calcs may be done for various cylinder volumes.

I have seen cylinder losses as low as 0.25C/hr claimed for some cylinders, mine (150 Litre) is 0.45C/hr.

Hot Water Cylinder Loss​	​	​	​	​	​
Kwh/24 Hrs at 60C​	1.6*(0.2+0.051*V^2/3)	where V is the Cylinder Volume
​	​	​	​	​	​
Cylinder Volume​	210​	Litres​	​	​	​
Heat Loss​	3.20​	Kwh/24hrs​	at 60C	​	​
Heat Loss​	13.12​	DegC/24hrs​	at 60C	​	​
Heat Loss​	0.55​	DegC/Hour​	at 60C	​	​