Hot water takes ages

[Handyman]

In due course, I (or more accurately, a plumber), will be installing a Megaflow hot water system in my house. This will reduce the time it takes for hot water to appear at the taps.

Now, this might be a stupid idea, but what's to stop me installing a sort of flow and return loop in 22mm connected to the hot water tank connections, with the various taps tee'd off in 15mm? The idea being that water in the pipe loop gets heated by convection from the water in the tank so that when I run a tap, the hot water is almost instantaneously present. Don't hotels have something like this?

In my case, the maximum distance from tank to tap is about 25m, and in the mornings, it takes several minutes to clear icy cold water before warmth is felt.

My attention to this issue is encouraged by my determination to reduce the staggeringly high water rates I am expected to pay.

 

[slippyr4]

Now, this might be a stupid idea, but what's to stop me installing a sort of flow and return loop in 22mm connected to the hot water tank connections, with the various taps tee'd off in 15mm?

Where you going to connect your flow and return? A megaflo won't be tapped for that.

And your main cost of hot water is actually heating it...

If you've got static water in a pipe, it cools down and you've wasted the heat. But when it's cool, you stop wasting the heat.

But if you're circulating fresh hot water through same pipes (except in fact there will be twice as much pipe), then you're going to be losing heat continuously. This is a waste of energy and will cost you £

 

[park]

You can buy the Megaflow with a primary coil, which could be connected to your heating system

 

[chrishutt]

You could have gravity powered secondary circulation, providing there is a suitable tapping on the cylinder. However the pipes would have to be well insulated to minimise heat losses, and the falls would have to allow gravity circulation. A check valve would prevent flow to the taps along the return pipe.

A better arrangement might be pumped secondary circulation, in which case the return pipe would only need to be 15mm and falls would not be critical. The pump would then only operate at those times when hot water is required. However I think a pump might not be permitted (Water Regulations) on what would be mains pipework.

 

[Handyman]

I did a test this morning: 3.5 litres of cold water came out of the tap before warm water appeared. Now, say 3.5 litres 3 times a day, times, say, 350 days, = 3.6cu. m/year. Down here in the SW that costs me about £12.
Hopefully, when I get round to installing the Megaflow system and re-routing the pipework, this must reduce by at least a half, so I suppose it's not so bad after all. It would cost more than £6/year to heat the water in the pipe and recoup the cost of the extra kit, so I won't bother pursuing my great idea.

Thanks to all for constructive replies.

 

[slippyr4]

As you've evidently worked out, the cost benefits of your idea aren't really worth it, but it's still an irritation, which is hard to put value on.

One thing to consider is that with a megaflo, since the water is at higher pressure, your long runs could be in 15mm, which will reduce the amount of water sitting in the pipes significantly and reduce the amount of time it takes to drain out the cold portion. Plus if you insulate the pipe the whole run it'll make things a bit better - it'll still be cold in the morning but it should remain pretty warm for serveral hours after that.

 

[ricarbo]

If you are trying to supply just one remote tap, might it not be better to install an instantaneous electric heater in that location? The flow rates aren't usually great, but you'd stop wasting water and energy.
If your hot water pipes are 22mm, you'd draw 2.5 litres compared to 1 litre if the pipes were 15mm, unless my maths is wrong (based on internal diameter of 22mm pipe is 19mm and 15mm pipe is 12 mm internal. If you could reduce down to 10mm it gets better still, but you might get a very poor flow.

 

[Diyisfun]

I find is the time waiting for the hot water to flow, more irritating than the cost

 

[CopperCylinderMan]

The building regs in Scotland mean that you cannot have a dead leg of more than 12metres without installing a secondary loop - the regs mirror those in England usually so it would be worth checking the local regs in this regard.

Its not the time for the water to appear that is important, but the length of pipe that is on the dead leg - whether your cylinder is a gravity one or an unvented is irrelevant.

You should check with local building control and follow their advice, and make sure you fit an unvented cylinder with a secondary return connection if required.

CCM

 

[Agile]

Er... Fife man! It IS the time taken for hot water to appear which bothers this chap!

The additional cost of a few pence a week is not important but its is annoying to have to wait.

His solution is to buy an unvented cylinder and use 15 mm pipe to the HW outlets. Thats cheap, has no running costs and will give speedy hot water.

The better solution is to use a pumped secondary and a cylinder which supports that. The running cost will be about £100 per annum but will give instant hot water.

Tony Glazier

 

[CopperCylinderMan]

Sorry Tony, it was the reply where the original poster said he wouldnt be pursuing his great idea due to the cost of the heat loss, and that it would be cheaper to waste the water, that made me think he wasnt fitting a secondary return.

My point was that while it may be inconvenient to have to wait for the water to run, it might also contravene English building regs NOT to have a secondary loop as 25m of pipe is too long a dead leg here in Scotland (and our regs usually mirror England after a couple of years of anything new).

CCM

 

[nickyross]

I did a test this morning: 3.5 litres of cold water came out of the tap before warm water appeared. Now, say 3.5 litres 3 times a day, times, say, 350 days, = 3.6cu. m/year. Down here in the SW that costs me about £12.
Hopefully, when I get round to installing the Megaflow system and re-routing the pipework, this must reduce by at least a half, so I suppose it's not so bad after all. It would cost more than £6/year to heat the water in the pipe and recoup the cost of the extra kit, so I won't bother pursuing my great idea.

Thanks to all for constructive replies.

The great idea is still great, IMHO, and chrishutt's secondary pumped circuit is one that I've seen implemented to good effect.

A customer called me because the loop wasn't working, and I find the fault that was subsequently put right by the installer. I then tweaked the system so that the pump ran only during the "DHW on" periods.

The customer had already decided that he wanted it, so I didn't need to work out the running costs, but Agile has, and his estimates (and his comments) look utterly reasonable.

Don't forget that the 3.5 litres of water that you pour away (before the hot water arrives at the tap) is actually water that used to be hot, so you're wasting fuel as well as water.

 

[slippyr4]

Don't forget that the 3.5 litres of water that you pour away (before the hot water arrives at the tap) is actually water that used to be hot, so you're wasting fuel as well as water.

Handyman worked out the cost for that as about £6/yr , which I found suprisingly low, so worked it out myself. But I came out at about the same figure.

So the cost saving for wasted heat and water is not really worth it, the only factor to consider really is the convenience.


Another possible solution, over the top admittedly:- If the boiler location happens to be near to the problem tap (kitchen?), then you could install a combi, use it's DHW service solely for the one tap, and use the CH side with conventional controls and cylinder for everything else.

 

[Handyman]

you could install a combi

Aaaahhhhhhh.......wash your mouth out

 

[slippyr4]

Aaaahhhhhhh.......wash your mouth out

Agreed, but it was a suggestion of combi driving a megaflo, so not quite so bad.