New boiler help

[ben]

Hello,

I live in a three bed house with my partner. It's a three storey property with a toilet on the ground floor and a bathroom on the first floor and radiators throughout. We've inherited an old central heating system which consists of a gas boiler, hot water cylinder and header tanks etc.

Next year we're looking to rip out and redo the entire ground floor of our house. As part of this project we plan to get rid of the existing heating system (the boiler is on the ground floor), and replace it with a combi boiler. I've read the combi boiler FAQ on this site and am happy with the compromises this brings.

My main concern is that of pressure/flow. Currently our cold tap in the kitchen doesn't have very strong flow. It's OK (a plumber did measure the flow and thought it was OK), but not fast flowing. We want ensure that we have a really good shower (on the first floor) and are concerned that there's won't be anough mains pressure to supply this.

A builder recommended that we use a Megaflo to resolve this, but I'm not actually sure we have a problem. I checked the mains pipe which runs from the front of the house and it's 15mm. Could this be restricting the flow?

How can I find out for sure if the mains pressure will be suffient for a good shower?

[Jim Alexander]

Measure how many litres/min flow you get from the cold tap in the kitchen and report back. Next time ask the plumber for the number, not OK. If you have doubts about the mains pressure at ground floor level you also need to find out the ground floor static pressure to gauge what the static pressure will be at first floor shower head level.

The builder is talking nonsense, the Megaflow won't resolve the pressure problem, it's the other way round, a Megaflo needs a good pressure/flow. Vented against unvented has been done to death here so look up the threads.

Jim A

[John Rumm]

Find you best performing tap and test the flow rate with a container of knows size and a stopwatch. If you are getting 15 lpm or less then any mains fed system will perform poorly without significant additional work. 15 - 20 lpm is marginal, and 20 lpm is usually fine.

It will yes.

Peoples expectations of "good shower" vary wildly.

[Ed Sirett]

Take a look at some of the FAQs below.

[Lobster]

...that's not to say you can't possibly get a perfectly OK shower if you have a 15mm rising main, more that it's a potential contributory factor if you find you have an unacceptably slow flow rate.

David

[ben]

Thanks for all your replies. I've just measured the flow rate from the kitchen tap: We get 5.7 litres/min.

I guess I now need to get a static pressure reading to see if the pipes are restricting the flow, or if there's just a lack of pressure in the mains. I did speak to Thames Water a few months ago and they said that there should be 1 bar of pressure in the mains...

[Paul Herber]

no, 3 bar is more normal, 4 bar is fine too.

[David Hansen]

On Mon, 19 Nov 2007 10:32:35 -0800 (PST) someone who may be [e-mail] wrote this:-

Even if you consider that an acceptable shower, consider what will happen to the shower flow rate when someone operates an appliance elsewhere in the house.

It seems to me that a storage system would be better, with just the kitchen cold tap fed from the mains. If the bedrooms are all upstairs then the shower should be there. I would try a gravity fed shower, but lay it out with an eye to converting it to a pumped shower if that proved desirable.

Around here the static pressure in the mains is five times that.

If that is all they are offering then I doubt if increasing the supply pipe size will make much difference to the pressure, though it may make quite a difference to then flow rate.

[Doctor Drivel]

That FAQ is 20 years out of date. Combis do not compromise. Want a one that can do 3 bathrooms? There is one there.

[Doctor Drivel]

They specify a minimum flow too. Usually 9 litres/min. It may be worth your while get a new 25mm main back to the stop c*ck. You will never regret it.

[Doctor Drivel]

Best a cold water storage system that adds value. An accumulator. This will provide the volume required and pressure at the static pressure of the mains. The accumulator is a large round pressure vessel. Or two small ones.One of these and combi solves many problems in the house if the water mains cannot be uprated.

He should firstly get the mains pipe sorted out. Doing that may bring dividends, and that is all he would need.

Then he needs decent combi boiler with decent flowrate.

[Jim Alexander]

So you have got no basis for combi, thermal store or unvented DHW without sorting the mains. Ten years ago I paid over £600 for a new 20mm connection. On the other hand you have a three storey house, ideal for a storage system with reasonable head. A possible interim solution might be to retain or improve DHW storage, but have a combi feeding only the kitchen sink initially if you are determined to have a combi.

Jim A

[ben]

We are a bit limited on space in the upper floor of the house (we don't have a loft) which has a big influence on our decision for a combi.

Our next steps are to get a plumber in to give us a reading of the pressure, then get the 15mm pipe upgraded if the pressure looks OK.

[David Hansen]

On Mon, 19 Nov 2007 12:22:14 -0800 (PST) someone who may be [e-mail] wrote this:-

A hot water cylinder, like any other source of hot water, should be situated near the tap used the most, which in a house is usually the kitchen tap. The second floor is unlikely to be the best place for a hot water cylinder.

[Lobster]

Presumably the plumber will cost? You can buy a pressure gauge for a tenner...

David

[John Rumm]

Indeed, did not intend to give the impression it was inadequate, only that it will have a bearing. I have a 15mm water main into the house and it can supply about 18 lpm, which while not ideal, is ok with our 35kW combi. One shower works very well, and it can just about manage two at once if you don't mind a drop in the force of the shower. Its not so good if the washing machine or dishwasher is filling while you shower though.

[John Rumm]

That is pretty poor really. IIRC the water supplier has a duty to provide a reasonable flow rate of at least 9 lpm.

Have you tried at other taps, such as an outside tap if you have one? Some kitchen taps have very small water paths, that can give overly pessimistic flow test results.

1 bar is the minimum really. If your static pressure is that low, then even a storage system may have problems in a three story property if you need to place a storage cistern at the top (1 bar is equal to 30' of head).

One quick test to try is can you block off the flow of the cold main by sticking your hand over a tap. You would not be able to do that if the pressure is much over 1 bar.

[Doctor Drivel]

[Doctor Drivel]

Neither is a storage system.

[Andy Hall]

It is if the pipes are run separately from the cylinder and the cold water feed from roof tank to cylinder is adequately sized.