water flow

[blindpugh]

I have to replace the c/h and bathroom in my 4 bed semi, 9 rads. Just getting some basic info together.

I have measured the water flow as, kitchen 16l/m bath 18l/m. Assuming pressure is ok what kind of flow could I expect from a decent combi?

Is there some kind of ratio to apply when looking at manufacturers stats?
ie makers fig for unit says 12l/m therefore reduce by x given above data.

Thanks

P.

 

[chrishutt]

You don't say whether the flow rates you recorded for kitchen and bath taps were simultaneous or not. If simultaneous (i.e. total flow rate 34 l/m), then I'd say your overall water supply was good and a combi would perform according to manufacturer's spec. If flow rates were with only the tap in question open, I'd be less sure. Best to check flow rates with at least two taps open.

 

[blindpugh]

No, that was individually. Just tried as you suggested and they both drop off. Bath 12l/m kitchen 7l/m. Not too clever huh?

 

[chrishutt]

Your supply pipe from the mains may be 3/8" bore lead, or one of the stop taps may be partially closed. If the former, you could ask your water company if they do a lead replacement scheme whereby they will replace their lead supply with 25mm polyethylene, providing you do same (at your expense) your side of boundary.

Otherwise your going to find that combi hot flow is affected by cold taps being turned on. not the end of the world, providing you have thermostatic shower valves. Another option would be to use an accumulator to "store" mains cold water upstream of your combi, but this is unusual and not many plumbers will know about it.

 

[Nige F]

another option would be to use an accumulator to "store" mains cold water upstream of your combi, but this is unusual and not many plumbers will know about it.[/quote] ...I know about them...me and mate were asked to install c/h + unvented...V. low water pressure+ flow....U/V cyl+ vessel costs £1500 trade and me M8 got the ticket for u/v Nightmare on Elm St.

 

[chrishutt]

But in this case an accumulator could be less than £30, depending on size. Any size (even 8 litre) has some benefit in evening out fluctuations. But I'm not aware of anyone using them in this context.

 

[blindpugh]

Thanks for the replies,

The incoming main does appear to be lead, as for replacing it I'm not sure. The stop cock is by the party wall in the rear lounge, I have a nasty feeling the feed runs under the house.

I think the only thing to do is call in three or four of the local installers and see what they can suggest. There are plenty of houses just like this one around here so there must be local knowledge.

As for the combi, I'm not commited to the idea, it's just that I have no choice but to renew and I thought it would be best to simplify a system that is old and been hacked around a bit over the years.

 

[ChrisR]

As I understand it, a "problem" with an accumulator is that someone has patented the idea! Yes you can buy a pressure vessel, but if you use it (or sell it certainly) you are infringing patent rights. You can buy tanks 80 -200 litres for a reasonable price, that isn't the problem.

 

[chrishutt]

Thanks for that, ChrisR. So who has the patent - OSO? I find that odd, since an "accumulator" is nothing more than an expansion vessel or anti-surge tank, a pretty standard item of equipment. Most unvented cylinders use expansion vessels, which will function as "accumulators". Surely all these applications aren't patented? At the end of the day (cliche alert!) there's nothing in practice to stop me or anyone else buying and fitting an expansion vessel for this purpose.