Shower option - cast your vote! Cold from loft tank VS Pressure Equalising Valve?

[Oxbow16]

First - an apology for monopolising the forum with all my plumbing questions! I'm hoping this will be my last and I'll move onto something else (like choosing a woodburner, which is the next thing on the to do list)...

 

My situation... We've having a bathroom refit and will have a new bath with shower mixer tap. We've got an oil boiler and vented system. We're eco minded and are happy with a very weak shower. In fact, that's our preference. So we don't want to install a pump, shower power, new unvented cylinder, etc. etc. There will be another shower in the house too. The cold is currently mains.

 

 

I've narrowed it down to two options:

1. Put a pressure equalising valve under the bath so the hot and cold have matched pressure.
2. Run a cold feed from the tank in the loft, so both hot and cold are gravity fed. (The tank is 40 Gallon actual / 60 Gallon nominal).

 

Some relevant points for both 1 and 2:

 

- Is a 40/60 gallon tank large enough to run the cold and hot from?
- The tank isn't far away from the bathroom ceiling, so wouldn't need a long run of pipe to get to he shower mixer tap
- The pipe from the loft would be coming down the tap end wall of the bath, so would need to be chased in / tiled over. However, the mains cold goes up to the loft on the wall too, so there's already a pipe being chased in there...
- The mains cold comes up from the room below where the bath will be (tap end)
- The bath panel will be removable, so accessing the PEV wouldn't be an issue
- Future proofing... Hopefully the boiler has years left in it, but if/when it goes we don't know what we'll go for next. Are PEVs useful in unvented and/or combi boiler set ups (when used with bath shower mixer taps)? I've read very opposing answers to that question!
- I presume performance will be similar in both set ups, so if there's likely to be a big price difference between the two then that might help decide.

 

I'll add a poll for the sake of it.

 

A vote, or a thought on any of the above, would be most welcomed.

 

Many thanks and have a great weekend everyone.

[Oxbow16]

Thanks to whoever voted   

 

Any the thoughts / votes from anyone?  

 

Cheers

[tonyshouse]

Run a new pipe from the cistern in the loft.

 

some modern mixer valves can cope with cold mains and hot from rank 

[joe90]

Not sure if this is correct but I was told years ago you were not allowed to run cold from a tank to a shower if the hot is mains pressure??. This was so that if the tank ran dry someone could be scalded as the hot continued to flow. ?…

[SteamyTea]

No help what so ever, but as 7 have voted, half votes must be allowed.

 

[Oxbow16]

5 hours ago, SteamyTea said:

No help what so ever, but as 7 have voted, half votes must be allowed.

 

 

That is odd.  And I see the totals don't add up either.  IE - in your quoted section.  2 votes for each (so 4), but total is 7.  And as it currently stands, 3 votes for each (so 6), but total voters is 9.  Maybe there's a hidden Brewster's Millions option for "None of the Above"?!  If you've not seen that film I guess that won't make any sense!  

 

5 hours ago, joe90 said:

Not sure if this is correct but I was told years ago you were not allowed to run cold from a tank to a shower if the hot is mains pressure??. This was so that if the tank ran dry someone could be scalded as the hot continued to flow. ?…

 

That seems sensible.  In my case hot is from the tank, but good to know these things nonetheless.  

 

6 hours ago, tonyshouse said:

some modern mixer valves can cope with cold mains and hot from rank 

 

That's interesting, I wasn't able to find any.  Do you have any links/suggestions by any chance?

 

Cheers for the replies 

[tonyshouse]

https://www.bristan.com › product-files › fitting-i...

 

PDF

 

Thermostatic Recessed Dual Control Shower Valve ... Gravity fed hot & mains cold(differential pressure, maximum ratio 5:1). Unvented systems.

28 pages

[Nickfromwales]

Go for tank fed, then, if you DO upgrade in many moons time, you just connect that to the cold feed from the tank and you get mains pressure cold to match the new mains pressure hot. Then you can just buy any good quality thermostatic mixer valve now and it will accept both gravity now, and mains later  

Edited September 29, 2021 by Nickfromwales

[Oxbow16]

Many thanks for the replies.

 

21 hours ago, tonyshouse said:

differential pressure, maximum ratio 5:1

 

That would be the problem....  Mains cold is 4bar and the hot will be somewhere between 0.1 and 0.2bar.  So well 20:1+!

 

20 hours ago, Nickfromwales said:

Then you can just buy any good quality thermostatic mixer valve now and it will accept both gravity now, and mains later

 

That's a good point and well worth considering.  Although that being said, we never really want a powerful shower so even with a unvented/combi system we'd want it turned down a few notches to save water and energy.  

 

 

So as to what I'm going to do, I'm still undecided....  

 

Does anyone have experience with PEVs and/or care to comment on how reliable they are?  

 

Are there any scenarios with an unvented or combi system where a PEV might be useful?  The product blurbs all say "suitable for unvented and combi systems," but from what I understand both of these have equal pressure, so why would anyone use one with those systems?  Does it change things if a shower/mixer tap is being used rather than anything thermostatically controlled?

 

Thanks again

 

Edited September 30, 2021 by Oxbow16

[Nickfromwales]

PEV is another wholly unnecessary item to fail at some stageIt will

also need removing and become redundant if you get a combi  
A good quality thermostatic shower will run reliably at low flow. Run the pipe to the tank.