Best solution to improving DHW

[Billyqureshi]

Hi. Sorry to ask this but other posts I’ve seen don’t cover my arrangement.

5 bed detached with two main bathrooms plus utility and another WC. Have a newish 40kw combi. Incoming water pipe is 15mm and good mains water pressure

internal pipe work copper with little bit of pvc from a previous extension job

problem - with one rainfall shower on, any other water demand reduces flow and heat in showers. Even a washing machine or a loo flush. Not acceptable to me

idea - add a water tank in the loft.

Questions - is this sensible ? What type of tank suits my needs the best? Would the tank supply all the DHW or would the combi still supply nearest outlets eg kitchen, utility, loo? Do they come with electric backup? Are there other options ?

Any help appreciated

 

[muggles]

What's your mains pressure & flow rate? Need numbers rather than just "good". Get your mains properly tested (or do it yourself) and that will guide you to what options you have.

https://www.screwfix.com/p/monument-tools-mains-water-pressure-test-gauge-11bar/82412

https://www.screwfix.com/p/monument-tools-water-flow-cup-weir-gauge/5784k?_requestid=12104

Connect the pressure gauge to an outside tap and turn it on. Need to know pressure with no taps running, and flow rate when the gauge reads 2 bar and 1 bar.

 

[Madrab]

Once the incoming pressure and flow are known then you may need to look at upgrading the incoming mains.

Even if you have an adequate mains supply then you would need to upgrade to at least a 22mm (25mm) mains to ensure enough cold flow so there is minimal drop off whenever multiples outlets are used.

 

[durhamplumber]

problem - with one rainfall shower on, any other water demand reduces flow and heat in showers. Even a washing machine or a loo flush. Not acceptable to me

If it is that big a deal for you,do not put the washer on or flush the loo whilst showering...

 

[sxturbo]

this is a classic issue with combi

 

[Billyqureshi]

Thanks for the comments . I will get accurate mains pressure and flow and report back.

 

[Billyqureshi]

If it is that big a deal for you,do not put the washer on or flush the loo whilst showering...

not a helpful reply.

 

[ScottishGasMan]

Do whats been said already with regards to getting figures, but you need to remember that combis regardless of power output are typically flow limited to some degree, there a low cost space saving measure for hot water, not the gold standard for it, so any effort to increase it may be futile. Would be usefull to know what make/model the boiler is while your at it.

 

[Billyqureshi]

Hi. Had a large plumbing company come out today. They didn’t take any formal measurements but felt I had adequate mains cold water pressure. He didn’t say anything about the fact my stopcock and internal pipe work is all 15mm.
My combi is a baxi duo tec 40 hea which is 5 yrs old. he suggested I could add a 200L indirect unvented megaflow in the loft. This would involve taking pipes from the boiler room straight up through its pitched roof (it’s in a downstairs-only extension) and then under the tiles roof to the side of the original building then some lagged piping up the external wall and into the loft space. Total pipe run would be a about 6-8m. He felt this would provide enough hot water to power two rain showers without any noticeable drop in performance. I’m not sure if he was referring to flow or pressure.
Does any of this sound reasonable ?

Nb he suggested a y plan arrangement for the new setup. My home is about 200m2 and has 15 radiators. I current have a one channel hive but he said that two channel version would allow hot water control.

 

[oldbutnotdead]

Your megaflow won't perform at its best with 15mm supply, you want at least 22mm from the stoptap coming from 25mm MDPE otherwise you'll still suffer flow drop when another cold tap is operated.
Apart from that, 200ltrs isn't massive for 2 showers especially with rainfall heads.
Sensible plan is plumb the megaflow to the showers only, leave kitchen & utility on the combi

 

[Madrab]

They didn’t take any formal measurements but felt I had adequate mains cold water pressure. He didn’t say anything about the fact my stopcock and internal pipe work is all 15mm.

Nope, nope, nope

Unfortunately it's not a gold standard test to stick a finger under the tap and then say, yep that'll do for an unvented, especially, as suggested when the supply is on a 15mm pipe. Your mains will need upgraded to a larger pipe and then tested to avoid any drop off in flow/pressure when more that one outlet is used and also to keep the velocity/flow noise to a min. You could get your water company out to confirm dynamic pressure and flow at the mains which will give you an ideal of what's available. Min of 2 bar @ 20L/Min to supply 2 good showers is a good starting point.

Your boiler's fine, no issue there and yes you can change it over to either a Y or S plan to service the HW cylinder with a 2 channel HIVE.

Depending on how long the showers taken are then a 200L high recovery unit should give you plenty of HW to do the job. A high output shower can use about 15L of HW a min but that can be further assessed by checking the target shower performance figures. Good idea, as mentioned, thinking about separating the HW and use combi element of the boiler to supply the kitchen sink etc

I would avoid taking any pipes externally unless it's encased in really high efficiency speciality lagging.

 

[muggles]

Hi. Had a large plumbing company come out today. They didn’t take any formal measurements

That's all I need to know. Call someone else

 

[Billyqureshi]

Thanks for the replies. I’ve done some flow measures. My outside garden tap gives 33 l/m and my bath cold tap gives me 21 l/m
I take the point about the plumber not taking any measurements and I will get them back before I agree to any work.
I don’t understand really what upgrading the supply entails. Is it just changing the piping from the isolating point to my stop cock?because doesn’t that just move the flow limiting part of my system further inside the home ?Or it is changing all the piping in my home ?
Really appreciate the help here.
Another question I had was do I need to take a new feed from the fuse box to where the tank would go?

 

[Billyqureshi]

Re the outside run of pipes - itd only be 1-2 metres. Are there standards or aspirations for lagging pipes / boxing them in so they’re not an eye sore ?

 

[oldbutnotdead]

You're very fortunate having that sort of supply. Your next test (tricky but worth doing) is checking the flow rate at the bath tap while the kitchen tap is running at full chat. If there's no significant change then probably happy days regarding your supply.
Heating pipes outside- yuck. You'd want an enclosure with minimum 150mm for each tube (so 300 wide x 150 deep) then aircon- style insulation for the pipes (thick closed cell heavy stuff) and consider putting trace heating wires on the tubes as well (hooked to a frost stat).
If I was doing such a thing I'd do the boxing in plastic trunking or marine ply, then clad it with brick pattern vacform or brick slips (so it looked like a flue in the wall). Worth trying really hard to not have the pipes outside...