Unvented how good? Combi how bad? H E L P !

[ChrisR]

If you're getting 14l/min from a 4 bar supply 6m long your equivalent pipe size is about 7 millimeters!
That's because of squashed lead, scale, closed taps, whatever.
Change it.
Bear in mind that your mains pressure at the road is likely to go DOWN over time, as they get better at controlling it, which reduces their leaks.
Also - accumulators have very limited capacity unless they're huge.

 

[batsran]

My Mother had a 1 kM supply pipe and a static pressure about 3 Bar but a flow rate of about 4 li/min !

Hey Tony - that must have been a long old garden !

Batsran - I'm by no means an expert (in fact about as far from an expert as you can get!) but when the guy did the flow test did he check that the two stopcocks were both fully open (the one in the road and the one in your house) as if either were partly closed it would restrict the flow?

Also, the tap he used presumably may also restrict the flow (the qualified people here may be able to give pointers on this) - or is this normally done by using an unrestricted pipe ?

My gut feel would be to upgrade the mains pipe for a permanent solution (I'm sure accumulators have their place but a pipe upgrade seems more logical if you can do it)

We've just had our place replumbed. The supply to the unvented was done in 22mm except for one 15mm section under he concrete floor which we will upgrade when we re-do the kitchen. Works fine for us as is but should be even better when we replace that last section of pipe.

One tip though. I'd get moving on the CH install asap. It took us a long time to find someone and as winter is approaching people get busy doing repairs etc and have less time for installs.

Much appreciated. The chap didn't test to see if the stoptaps were both open - but he did the test on the garden tap (directly outside kitchen window where mains comes in) and repeated the flow test in the house on our pretty mixer taps. Both seemed the same. The general stance was as long as we were getting more than 10 l/min at 1bar static there was no issue!

I know our internal stoptap is fully open, but on the street its under a weird cover that looks like a special tool is required for opening (or possibly two giant 20p coins!).

As for getting a move on, I'm with you on urgency - its just I don't want to through £6.5K in the wrong direction!

 

[batsran]

If you're getting 14l/min from a 4 bar supply 6m long your equivalent pipe size is about 7 millimeters!
That's because of squashed lead, scale, closed taps, whatever.
Change it.
Bear in mind that your mains pressure at the road is likely to go DOWN over time, as they get better at controlling it, which reduces their leaks.
Also - accumulators have very limited capacity unless they're huge.

Thanks Chris. Its pretty depressing really. I am beginning to wonder if its worth going for unvented. Since the water board could reduce it down to 1bar with 10l/min that I guess would make the whole think terrible. I am starting to wonder if we should look to stick with a new gravity fed system. I still have the headache of relocating where the hot tank would go.

If we kept the cold tank in the attic and installed a 200ltr tank in the garage (directly attached to our house) - how effective would the flow be? Currently the tank is on the landing and can supply the baths at 20l/min. We already have a powershower pump.

Thoughts anyone? - it just feels like the only advantage to a sealed unvented is no tank in the attic and good showers without the need for a pump - but for everything else (like filling the bath) an unvented would struggle to compete with a gravity fed system (which provides constant flow, no matter what happens on the street!).

 

[Agile]

The other solution is to use a Grunfoss Home Booster located in the garage.

Thats a potable tank and a booster pump which gives about 3 Bar pressure and a good flow rate from the stored water ( until its exhausted. )

You can then use an unvented cylinder!

Much appreciated. The chap didn't test to see if the stoptaps were both open - but he did the test on the garden tap (directly outside kitchen window where mains comes in) and repeated the flow test in the house on our pretty mixer taps. Both seemed the same. The general stance was as long as we were getting more than 10 l/min at 1bar static there was no issue!

Thast the problem! Plumbing used to be for those who were not very good at school! Many of them just dont understand whats required and are too keen to get the job ( and your money ) that they dont bother themselves as long as a little water will come out of the taps.

When it does not work properly they will then tell you you have to spend another £1200 to get the supply pipe upgraded!

You need 20 li/minure DYNAMIC flow rate for an unvented to work properly! Dynamic means 20 li/min with a residual pressure of say 1 Bar !

Tony

 

[simond]

On balance I guess I'm hoping that a new water main would be better than an accumulator - but again this is from a position of ignorance, assuming it would be another device that needs servicing and ultimately replacing in the fullness of time.

If you'd seen one working you might think differently.

Unfortunately you are outside our installation area but I can arrange a demo on the Kent/Surrey borders, providing you post your findings here!

There will be installers in Hertfordshire who are conversant.

 

[batsran]

On balance I guess I'm hoping that a new water main would be better than an accumulator - but again this is from a position of ignorance, assuming it would be another device that needs servicing and ultimately replacing in the fullness of time.

If you'd seen one working you might think differently.

Unfortunately you are outside our installation area but I can arrange a demo on the Kent/Surrey borders, providing you post your findings here!

There will be installers in Hertfordshire who are conversant.

Hi Simon - thanks for the offer. So if the street static pressure to the house reduced from 4bar to say 2bar - what would the effect be if I had an accumulator. It seems that the focus is on the boost to flow rate, but I get the impression that accumulators have a balloon inside that relies on the water pressure to compress in a one way valve and then when the demand is needed it squirts the pressurized contents to supplement the mains feed. All of these tanks etc seem to only promise water at 20l/min as a guide for hot - so please; can someone tell me why to consider anything other than a gravity fed system that is happy for the cold tank to drip fill and never affect the hot water feed? - is this all to get away from needing a pump for the upstairs showers? I feel that I am missing something obvious here!

Probably an impossible question, but if I had a 200l unvented system - what size would the accumulator need to be to ensure 20l/min for say a 7 min shower - and what would be the recovery time for the accumulator for someone else to then jump in the shower and enjoy the same flow rate (I have not done the maths here to see if a 200l unvented system would be ready with more hot water, but I'm guessing that hopefully the hot tank would recover in less than 20mins). In a nutshell I would like to know if the accumulator recovery time would be noticeable (assuming my existing 14l.min @ 4bar was retained via the 15mm mains feed).

Thanks everyone who has bothered to keep reading this!

 

[Agile]

Whatever you get out of the accumulator has to be put back!

If there is no other water demand it will refill in about [ 0.75 volume in li ] divided by [ 0.5 times the flow rate into the property ] giving the answer in minutes.

So for a 200li accumulator [ active volume 150 li with 4 Bar mains ] and an open pipe flow rate of 10 li/min it will fully recharge in about 30 minutes.

A new mains supply does not need to recharge!

Tony

 

[lagunaglen]

The 15 mm main you have coming in,are you sure its not a bigger pipe under the floor, ive fitted a dozen or so unvented and have usually found that after taking floor up the pipe size is adequate and only required upgrading stop tap to 22mm.
This may be just me who is lucky or the area im in.(Doncaster)

 

[batsran]

Thanks for the details on the recover time for the accumulator.

As for the mains coming in, I'm pretty sure. We had a look under the kitchen units and its a copper 15mm pipe coming out of the concrete floor

Can anyone tell me what advantages a unvented system offers above gravity fed ? Is it only the space saving in the attic and possible increased pressure to the upstairs showers, with the minus being longer to fill baths?

Could a hot tank be downstairs for a gravity fed system and still work? - would the existing flow of 20l.min then be reduced?


Thanks all.

 

[Agile]

Can anyone tell me what advantages a unvented system offers above gravity fed ? Is it only the space saving in the attic and possible increased pressure to the upstairs showers, with the minus being longer to fill baths?

Could a hot tank be downstairs for a gravity fed system and still work? - would the existing flow of 20l.min then be reduced?


Thanks all.

An unvented gives mains pressure hot water which is good for powerful showers to give that tingling effect. ( No, not that one ! )

A vented can be placed anywhere but the pipe sizes have to be large to get a good flow. ( Always 28 mm feed ) 20 li/min into bath is possible but it needs full flow taps.

The cistern has to be in the loft and if its raised that maks a big difference.

Tony