How long should you run boiler to heat cylinder?

micks_address

Hi folks,
May be a silly question. We have a standard size copper cylinder. Two zone system where we heat rads and water separately. We run the water for 30 minutes in the morning. 30 minutes mid day and 30 minutes in the evening. I’m wondering would it be better to run for longer than 30 minutes? Maybe 45 minutes or an hour? I suppose the boiler would cut out once the water reaches the set temp anyway? Just feel like 30 minutes might not be heating the water fully.
Thanks,
Mick

10-10-20

So many answers to this one.
Is the cylinder well insulated? Is the amount of hot water in the tank last for the day or do you regularly deplete it or is it losing heat to the surroundings (hot-press)?

Looking at this from an efficiency angle, the best approach would be to heat the water to between 50 to 55 degrees C once in the day.
https://www2.hse.ie/wellbeing/child-health/burns-and-scalds/preventing-burns-and-scalds-from-liquids.html
This would be the most efficient method as you avoid heating the piping and circulating water up excessively.

This temperature is a trade-off between a safe temperature (in terms of scalds) and risk of legionella.
https://www.hse.gov.uk/healthservices/legionella.htm
Of course you can heat it higher if needed.

In my case I have the gas heating the cylinder for 1hr 20 from 06:00 so that the cylinder is ready for the showers to start at 07:20. It gets from ~25 degrees to 50 degrees in that time (a 300l tank). That way I also avoid any losses in having hot-water sit unused for a duration before the showers (the hotter the tank, the greater the losses through the insulation).

And yes, newer boilers will either modulate the flame or cut-out once the cylinder has reached the required temperature (do you have a cylinder stat?)

micks_address

10-10-20 wrote: »

So many answers to this one.
Is the cylinder well insulated? Is the amount of hot water in the tank last for the day or do you regularly deplete it or is it losing heat to the surroundings (hot-press)?

Looking at this from an efficiency angle, the best approach would be to heat the water to between 50 to 55 degrees C once in the day.
https://www2.hse.ie/wellbeing/child-health/burns-and-scalds/preventing-burns-and-scalds-from-liquids.html
This would be the most efficient method as you avoid heating the piping and circulating water up excessively.

This temperature is a trade-off between a safe temperature (in terms of scalds) and risk of legionella.
https://www.hse.gov.uk/healthservices/legionella.htm
Of course you can heat it higher if needed.

In my case I have the gas heating the cylinder for 1hr 20 from 06:00 so that the cylinder is ready for the showers to start at 07:20. It gets from ~25 degrees to 50 degrees in that time (a 300l tank). That way I also avoid any losses in having hot-water sit unused for a duration before the showers (the hotter the tank, the greater the losses through the insulation).

And yes, newer boilers will either modulate the flame or cut-out once the cylinder has reached the required temperature (do you have a cylinder stat?)

Thanks,
Yes it’s well insulated. New boiler only fitted 2 years ago. There’s a stat on the cylinder for sure. We have nest for scheduling. I’ve just noticed few times we have boosted the water for say an hour it’s way hotter in the taps. It’s hot at 30 minutes but maybe I’ll try 45 minutes for a few days and see how it goes. We have an electric heated shower.

Tank is 150 litre or whatever standard size would be
Cheers
Mick

John.G

A 150 Litre cylinder with a standard coil will take around 40/50 min to reach 60C from ~ 25/30C, suggest you leave it programmed on for a hour, the boiler will/should be shut down by the motorized valve when the cylinder stat is satisfied so very little or no energy wasted.

K.Flyer

If you have a cylinder stat and all is wired correctly then you should only run the the gas boiler on the hot water demand to produce enough hot water that you need.
So ask yourself, when / why do you need hot water?
For example, do you need hot water in the mornings and / or evenings for showers / washing.
Let's say you mainly need hot water for showers in the morning.
Then run the boiler for the 30mins (if that provides enough hot water for showering) before you need the water, likewise if you want showers in the evening.
Then why are you timing the boiler to heat water at other times?
If the answer is mainly for washing hands consider using the immersion heater on a timer for 15 - 20 mins on sink. On a well insulated cylinder this should provide sufficient hot water for that and you are not wasting energy heating up the heating system for a small amount of hot water.
Save energy and only create just enough hot water for what you need and just before you usually need it.

Sleeper12

Just to add to the points above. It's slightly more economical to heat the water at a time when you would have the heating on rather than running the boiler just for water.

At this time of year our heating is timed for an hour early in the morning to take the chill out of the house by the time we get out of bed. I have my hot water zone on at this time too. This gives us a full tank of water to start the day. With four adults in the house this isn't enough to last us the day with showers and stuff but it gives us a good start