New Bullshit - Flowsave. Get one now

[Grimly Curmudgeon]

Biggest piece of bullshite I've seen since magnetic water softeners - oh, you can buy one of them from the same stockists. What a surprise.

[Clive George]

The concept looks like it doesn't break any laws of physics, unlike magnetic water softeners. So the product itself doesn't look as much like bullshit as you say.

Their claimed savings stink though.

[Grimly Curmudgeon]

It runs the cold water off the hot leg, slowly, until the hot water reaches it, then opens full. What's the point of that? You still lose water. The hot water in the leg still cools. You end up losing as much water down the drain as if it wasn't there at all.

[harryagain]

I fail to see how it can save anything.

[The Medway Handyman]

And only £60 odd quid!

[Nick]

You turn on the hot tap, presumably you want hot water. The heat exchanger on the water heater takes time to be heated to working temperature, until that time the water passing through will not be heated sufficiently. Hence by limiting water flow until it can be heated you are saving some of the unwanted cold water that would otherwise flow through the system. Simples.

If it really provided significant savings they would implement it in the water heater.

[Chris Hogg]

I have a version of it. Manual, not automatic though. It's called a tap.

[Brian Gaff]

Hmm, so how does spreading the usage over more time save money? After all in the end its the same amount of water you are heating up. Very odd. As for magnetic water softeners. I understand that the ones that use a high voltage alternating field can in fact clog the pipes near them as what happens is that the bits of limescale etc, clump together, similar to how air particles do near high voltage cables.

Oh dear. Brian

[Brian Gaff]

Exactly my thoughts. In the end the thermal lag is just spread out more. It seems to me it will take longer to actually heat the whole water mass to the temperature, though the heat exchanger might get to the working temp faster under some conditions. Brian

[Mike Barnes]

If there were a reservoir of water already up to temperature I'd agree with you. But it's for heat-on-demand systems. AFAICS the heat exchanger will get up to temperature more quickly with a reduced flow of cold water entering it.

[PeterC]

I have one and it works, but mine was free: I've always run the DHW from the combi at a rate that gets the boiler's up and running and then increased the rate to a balance of flow and desired temperature. I wonder if I could make money by charging for this method printed on a bit of paper and posted to the suc... sorry, customer.

[Tim Watts]

OK - I hate to say this - but it will have a positive effect.

T0 = time tap was turned on T1 = time boiler heat exchanger gets up to 42C t0 = inlet water temp V = volume of pipe between boiler and tap F = normal tap-on flow (mass-flow) f = restricted flow s = SHC of water

With or without this device you will waste L of cold water - unavoidable unless you have a loop.

However what this is doing is to save you:

(F-f)(T1-T0)(42-t0)s joules by slowing the flow enough to allow the boiler flow switch to activate whilst it gets over its thermal lag.

Net result is you get cold water for a bit, then more or less hot water rather than cold water, then tepid water then hot water.

So what's it save?

Guesstimate figures:

t0 = 5C (T1-T0) = 5s F = 0.2 kg/s s=4200J/kgK

so (42-5) x 0.2 x 5 x 4200 = 155kJ = 0.043kWh

is roughly 0.3p at 7p/unit for gas boiler

And that's only for when the boiler has cooled down. Repeated tap activations in succession are not a saving.

So it will take 20,000 tap activations to pay for the device and perhaps

50,000 to pay for the device plus a plumber to install it. *FAIL*

OK - I did not factor in water savings for water meters, but next to bugger all would be my considered estimate there.

[News]

In message , Nick writes

I have no experience of combi boilers but, it seems to me that one could achieve the same result just by partially opening the tap until the heater is at working temperature, and hot water flows, at which point open the tap further, or fully, as required.

[mike]

Doesn't the modulating part of the boiler adjust the heat input to flow rate for optimum efficiency anyway?

[Tim Watts]

Exactly my conclusion.

And after 20,000 such "savings" the unit will have paid off its £60 cost. Unless you pay a plumber to install it...

[Mike Barnes]

VIPs (Very Impatient People) will also have got their hot water a second or two earlier, 20,000 times. Say two seconds times 20,000, that's almost 12 hours less waiting. Bargain.

[Jethro_uk]

Following the comments in the thread, it seems that one of these is already built in to my (12 year old) combi boiler. It restricts the water flow until the hot water has got to temperature.

[The Other John]

There's another one here:

Didn't notice any savings figures, only water in the video.

[John Rumm]

Some combi's in effect do, by keeping a small store of tempered water to provide more "instant" heat.

[John Rumm]

Assuming the boiler is cold when you turn on the tap. The boiler then needs to bring the HE and the small amount of primary water in the boiler circuit through the diversion valve and the PHE up to temperature, which will take a few seconds. If during that time you are running DHW through the other side of the PHE at full rate you may end up with several litres of "warm but not hot enough" water that you waste. By limiting the flow through the mains side of the PHE while the heating up is happening, you reduce the amount wasted... a bit.

Whether the sums ever add up enough to make it pay is another matter!