Advice - fitting thermostatic mixer shower

[cjbell68]

Hi, I'm looking to add a mixer shower in our bathroom to supplement the electric shower in the en-suite. Household of 4 with two children 9 & 12. A flow of anywhere from 6-10 litres/minute blended seems like it would provide a nice shower - with the opportunity to have a higher temperature than the current electric shower can produce at ~6l/M.

Current situation
Open vented system
Baxi Solo 50 RS running Y plan HW + CH (4 bed house with 14 rads)
Albion CF45 super duty High recovery hot water cylinder
Cold water storage tank is round - diameter at top 75cm, height about 60cm. So I estimate this holds maybe 160 litres?

I don't want to change the boiler until it dies (even then only for a condenser - not a combi), and I don't want the expense of fitting an un-vented cylinder - or the ongoing maintenance costs. I don't want to fit an electric shower as I wanted to fit something a bit better - and it seems a good idea to increase the cylinder capacity because the children will use more water when they get older anyway.

I'm thinking of taking the following steps:
Step 1
Replace the small cylinder with a much larger high recovery one.
There looks to be room to get a 1200/375 or 400 cylinder into the airing cupboard (445/470 with insulation). This suggests a cylinder capacity of 120-136L would be possible and gives the opportunity to get one I can easily fit a flange to or specify a shower take-off flange be built in (current cyl. has built in mail 22mm compression outlet for the hot water/vent). Thinking Gledhill Envirofoam or Newark.

Step 2
Fit a thermostatic mixer capable of working with either high or low pressure and see if I can get a reasonable shower from it (seems doubtful).

Step 3
If required add a pump to the system - e.g. 1.5/2 bar Stuart Turner Monsoon (hopefully standard but more likely universal - but I can measure the HOT / COLD flow rates from the mixer once in place).

I imagine limiting the shower by fitting reducers between the pump and shower would be a good idea, we could set it up for a reasonable flow rate, but not so much as to drain the cylinder quickly. My son has a habit of staying in the shower far too long which risks draining the tank.

I need to run the shower pipes up and over through the loft the down through surface mount chrome into the mixer. This suggests I may need a pump (poss neg. head) next to the hot water cylinder.

I've had a good look on the forum already so have seen the requirements for a separate cold water feed from the loft tank - and where to site this. Also it MIGHT be necessary to switch from Y Plan to W plan - although I would probably just run the HW independently with CH off to ensure enough heat to keep the cylinder topped up.

Questions
Does this seem a reasonable course of action? Is there anything else I need to check or other courses of action I could consider?
For example does the hot water cylinder need to be larger or is it sized ok - also high recovery seems a good idea? (Adults shower in the morning and children in the evening at present - few baths. Washing machine & dishwasher cold feed only).

All advice/views welcome

Thanks in advance
Colin

 

[mogget]

I think you've got two possible courses of action here.

1) Keep the Superduty and change the boiler. I've just taken out a Superduty cylinder from my own house as the 18kW boiler could not heat the water quickly enough to run a bath in the winter (we have a large bath). It was cheaper for me to change the cylinder than upgrade the boiler. With a powerful boiler the only limit on your hot water would be the size of the cold water cistern in the attic.

2) Keep the boiler and change the cylinder. If space is limited you might not be able to get enough stored hot water for a long power shower. You'd need to measure the capacity of your bath, by measuring the flow rate from the cold tap, then timing how long the bath takes to fill. You need half the capacity of the bath in hot water.

If your boiler is coming up for renewal I'd be tempted to say keep the Superduty and get a 28kw (or more) boiler. Your choice though.

Disclaimer: I am not a professional, just an experienced DIYer.

 

[mogget]

One extra point, bear in mind that you don't actually get the full cylinder capacity in hot water, as you only generally heat the top 2/3rds of the tank.

 

[cjbell68]

Thanks for the replies Mogget.

I think I'll change the tank - I assume I'll take a hit on a longer recovery time, but hopefully can ensure there's enough hot water when we need it by changing the HW timing.

Can anyone provide their feedback or suggestions regarding what size of tank to go for - and if my approach regarding the new thermostatic shower makes sense?

I appreciate that a lot depends on our individual needs, but wanted to get confirmation on a reasonably sized cylinder - and whether I would manage with the current boiler etc.

Thanks
Colin

 

[bolshy]

Have you considered a thermal store? They can be fitted to Y plan or a sealed heating circuit with it's own pump. On direct stores, boiler heats store directly. Store provides CH directly, and indirect HW coil. HW is at mains pressure through a TMV. No shower pump, fit a standard mixer shower. No unvented maintenance.
What's your cold mains flow rate, good?

 

[cjbell68]

Hi
Have seen thermal stores mentioned on here but wasn't overly keen - perhaps because I found some posts where they weren't considered favourably. The term sludge bucket seemed to have been mentioned a few times separately. I don't know enough about them personally to form an opinion; I was looking at changing the cylinder as I would remain with a system I was familiar with.

I think mains pressure is good but don't know the flow rate. The tap on the incoming main is turned down somewhat to reduce the flow.

Are there any specific pro's / con's to a vented cylinder vs a thermal store I should consider? Is the thermal store still vented? Also would a thermal store be able to run two mixer showers in future (with regard to maintaining output temperature)?

I'm also still interested to see any other feedback people may have with regard to my original proposed approach - so I can see if this is a sensible option to include - or if I should modify or scrap it.

Thanks,
Colin

 

[cjbell68]

Hi
Anyone got any specific advice they could give regards:

Sizing the hot water cylinder/system for a power shower? for example
-How big a hot water cylinder?
-Is the cold tank big enough?
-Is a 1.5/2bar pump enough?

Thanks
Colin

 

[cjbell68]

Was really hoping someone could give advice on whether or not my initial proposal would work, and if it needs changing in any way?

Hope someone can help - I appreciate the advice I've received so far, but no direct response to the initial query.

Thanks in advance
Colin

 

[bolshy]

You are stuck with the physical limitations of the cylinder size you can install. A larger high recovery cylinder will obviously give you more hot water, and I would consider installing a second cold storage tank linked to the first to increase capacity for the shower and keep costs down.
You need to limit the water usage from the mixer shower. I would do this using a pulsed shower head.

http://www.sbw.savewater.co.uk/Shop...CO_Nordic_Eco_9lpm_Pure_Pulse_Showerhead.html

Savings are around 50% usage, with no aeration, and very good velocity.
You will need a flange on the cylinder, and a shower pump. 1-2 bar is plenty. These heads deliver a constant 9 litres per min at pressures above 0.5 bar.

 

[mogget]

OK, now we have a flow rate = 9 litres/min

So if you (say) want a 20 minute power shower you need:

20 x 9 = 180 litres of water. The cold tank in the attic needs to be this size or greater (as it supplies both the hot and the cold water for the shower)

You need half this amount in hot water = 90 litres. But you only heat 2/3 of the water in the tank so you need to add half as much again = 135 litres, so your cylinder needs to be this size or greater. This would be a 1050x450 cylinder at 140 litres. A 450mm cylinder is actually 520mm in diameter because of the foam coating.

If you want some water left over for washing up you need to accommodate that too.

Plug your own numbers into the calculation and see what you get but I suspect you may be looking at some fairly large tanks.

EDIT: Just looking again at what Bolshy said, that is the eco-shower-head at 9 litres/min, if you are using a standard shower head you may want to double it.

 

[cjbell68]

Thanks Bolshy & Mogget for your helpful posts!

I think I'll go with the original plan - but I'll get a larger cold water tank as well so it's able to meet the total output requirements.

That, coupled with the right mixer should do fine.

Thanks again for your help
Colin