Water Cylinder Size?

Dominic-Toretto · 6 May 2020 at 10:57

Hey,

I am looking for a new directly heated water cylinder for my home. What I am stuck on is the correct size of water cylinder.

Reading around online I can see suggestions of 30 to 45l per person, however it also states that a mains pressure shower system can use about 18 litres of water per minute. Which means 180 litres gone in 10 minutes. This makes a 400l tank seem small for even a 3 person house hold. I do not want the water going cold and then having to wait for it to heat up at any point during the day. Like wise I do not want the immersion heater on 24 /7. What would you guys suggest, does it really cost that much more to heat say a 500l tank vs a 300l tank? Once a tank is heated, how is it much cheaper just to maintain that heat via the tanks inbuilt thermostat?

Any input from plumbing experts?

Dandle · 6 May 2020 at 14:56

Don't forget that the shower will be mixing water from your tank at 55-65 degrees with cold water for your shower so it wont drain that quickly. I have a mains pressure 310 litre cylinder heated by my boiler, I purchased the bigger one as it was only a little bit dearer than the 210 and 180l cylinders. In hindsight I should have gone for the 210 as they recover so quickly with a boiler (about 20-25 minutes), I don't need to 310l of heated water in one go and they are considerably smaller.

peige · 6 May 2020 at 15:22

I have a 210 litre unvented Megaflo heated by a 30kw boiler. It only runs out if we hit it very hard, serving two bathroom showers when we get to three adults having showered it starts to run out but recovers very quickly (10 mins maybe)
I'd agree with Dandle, its at least double that time with maybe 30mins of running shower for us.

Much better than a combi job though, we don't have problems everytime somebody flushes the loo downstairs or if two showers are going at the same time (just a small drop in pressure)

Alex_L · 6 May 2020 at 16:14

We have a 210l for a 5 bed house and never had any issues with lack of hot water. The recovery time on them with a new boiler is so short I think we could have got away with a smaller tank but I erred on the side of caution. The Worcester bosch boiler our plumber installed also had a combi function so the kitchen taps are on the combi (heats on demand) and the unvented cylinder only serves the bathrooms which seemed a very clever solution when he did it and further reduces the risk of running the cylinder down

b0rn2sk8 · 6 May 2020 at 19:48

Are you heating on electric only?

All the comments so far are from those with boilers where it doesn’t really matter if you check the HW on a few times in the day.

if your on electric only and utilise Eco 7 then you’ll want to go big so you can take advantage of cheap off peak rates. Modern cylinders should say hot all day without any problems, it’s just how much water you’ll use in a typical day.

Orionaut · 6 May 2020 at 20:13

Squidward said:
Hey,

I am looking for a new directly heated water cylinder for my home. What I am stuck on is the correct size of water cylinder.

Reading around online I can see suggestions of 30 to 45l per person, however it also states that a mains pressure shower system can use about 18 litres of water per minute. Which means 180 litres gone in 10 minutes. This makes a 400l tank seem small for even a 3 person house hold. I do not want the water going cold and then having to wait for it to heat up at any point during the day. Like wise I do not want the immersion heater on 24 /7. What would you guys suggest, does it really cost that much more to heat say a 500l tank vs a 300l tank? Once a tank is heated, how is it much cheaper just to maintain that heat via the tanks inbuilt thermostat?

Any input from plumbing experts?

18L/m =/= 18L HW/m

A standard HWC 210L will be fine. you would need to be running a B&B/Hotel to need anything larger.

Dominic-Toretto · 7 May 2020 at 16:48

b0rn2sk8 said:
Are you heating on electric only?

All the comments so far are from those with boilers where it doesn’t really matter if you check the HW on a few times in the day.

if your on electric only and utilise Eco 7 then you’ll want to go big so you can take advantage of cheap off peak rates. Modern cylinders should say hot all day without any problems, it’s just how much water you’ll use in a typical day.

Hi mate, yes electric only. Based on electric only would you larger than 300l?

Participant · 10 May 2020 at 08:20

Family of four and we went for a 300L cylinder for peace of mind and because the incremental installation cost over a smaller cylinder was negligible.

We run the hot water all the time so it's always hot, which is rather inefficient but I hate running out of hot water.

We have two young kids who have baths and both enjoy long hot showers, and we've also started running warm paddling pools for the children (never happened in my day brr brr).