Thermostatic mixer shower instalation

[sengaul]

Hi all

Just wanted to confirm something regarding thermostatic mixer shower. A freind has asked if I would help them install one. They have a gravity fed system (CW = tank, HW = cylinder) and do not want electric shower.

Am I right in saying it is better to take the cold feed from the CWSC (below the height of the cylinder feed on the CWSC), and the hot feed T'd as close to the cylinder as possible, rather than T'ing off of supply branches in the bathroom? And is it better to use 22mm reducing to 15mm or just using 15mm.

Thanks in advance for any replies.

 

[Plumbstar Tom]

First question is answered yes and second will not make too much of a difference

Hi wont get as good a flow than he would with an electric shower but you could also fit a pump

 

[WHPES]

Hot feed should come off the cylinder directly using an Essex or Surrey flange.

Both hot and cold should originate from the same header tank.

You are correct in stating that the cold comes off lower than the hot - this is a safety measure to prevent accidental scalding if the tank runs dry.

Best to plumb in as much in 22mm as possible.

Pump will give a better flow than an electric shower.

 

[Scottwood75]

Also if you measure roughly the height of the outlet of the CWSC you will be using for the shower to the floor of the loft, and then the top of the shower rose to the ceiling, add these two together and you will get the head pressure.

10 metres = 1 Bar pressure
5 metres = 0.5 Bar

If you was lucky, id say you might get half a metre at best, which if I'm correct, which im not, Tom is, would be 0.05 bar (0.5M = 0.05 Bar)

If you get good supply pressure, you can sometimes add 0.5M or half the cistern height to the calculation.

You will need to read the manufacturers instructions to see the minimum flow rate or pressure. He might not have enough. Unless the shower is down stairs somewhere of course.

Also a boosted system would be best as previously mentioned.

 

[Plumbstar Tom]

If you was lucky, id say you might get half a metre at best, which if I'm correct would be 0.01 bar (0.5M = 0.01 Bar)

0.5meters head is approx 0.05bar

 

[Scottwood75]

0.5meters head is approx 0.05bar

Oh yeah, because 1M would be 0.1bar? right?

Cheers still not used to it yet

 

[Plumbstar Tom]

no probs

Divided the head height by 10 gives you and approximate bar pressure

 

[sengaul]

thanks for the replies.

I'll look into it some more regarding the height of tank and pressure he gets.

Does the hot need to be connected to the cylinder via an essex/surrey flange? Am I wrong in thinking you only connect via these if installing a pump?

One last question, hope I don't confuse you. If a second shower was to be installed (on this system) would you need independant connections to the CWS and cylinder, or could you have one shower connected and then branch off from these to the second shower? and if you could I assume you would need to install a pump before the branching?

 

[Scottwood75]

I should think they would each need a dedicated supply incase they are both in use and one gets starved of water, then again you could calculate the loading units, design flow rate and then select a pipe size that would suit?

EDIT: would I also be right in saying you may need to increase the size of the cold water storage cistern for two showers?

 

[sengaul]

thanks for the replies, I went and had a look at the CWSC the other, the tank has been raised as high as possible in the loft already (giving about 0.2-0.3 bar on the shower heads) but i noticed that the feed to the cylinder comes directly from the bottom of the CWSC? so i would not be able to run an independant feed lower than the cylinder feed.

I know the tank should sit on a solid 18mm base with the base overhanging 150mm from each side of the tank, but if I am to install these showers am I right in saying that I should be changing/correcting the CWSC if they are willing to pay, if not should I just write an advisory and get them to sign to cover myself?

 

[WHPES]

Yes you must correct this (you will need to remove the tank to drill another hole in the base anyway).

You must also bring it up to WRAS standards before recommissioning it (thermal jacket, sealed lid, breather and insect screen on overflow, Part 2 float valve and correct heights of fill and overflow plus all other Water Regs requirements)