In hot water

[Bill Wright]

Our combi boiler is a long way from all the taps, which are all at one end of the house. The reasons are historical, and also quite hysterical, but that's beside the point. I stand there drawing water off for ages before any hot comes, and it annoys me. I'm seriously considering fitting a conventional electric immersion tank very near to the taps. So, I need to work out whether it would ever pay back. I'm not one for doing these things just for show, like those people who put a wind turbine on their roof. The tap is turned on about four times per day when the water in the pipe is cold. The volume of cold water that comes before the hot (and thus of course the volume of hot left to cool in the pipe) is seven pints. I can find out the total cost of getting an immersion tank fitted. What I don't know is how much it costs to heat a given volume (a gallon, say) of cold water. The boiler is fairly new and runs on a big gas tank in the yard. The water supply not unusually warm or cold. The hot water needs to be good and hot, which is it at the moment once it comes. I am prepared to exclude any savings made when the water in the pipe is cool but not cold, and just calculate on the basis of the freezing water that I get when the system hasn't been used for hours.

Bill

[Nick Holmes]

Well it takes approx 4.2 Joules to heat 1gm (1ml) by 1 degree centigrade, so assuming your hot water is 60 degrees above ambient then I gallon requires about 1134 KiloJoules. If your boiler is 90% efficient this ought to take about 0.35 Kwh to heat LPG cost about 2p.

best wishes

Nick

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[Ron Lowe]

Bill,

Here are the options as I see it:

1) A source of hot water near the tanks;

2) 'Secondary Circulation'; a more complex arrangement where we pump HW around a loop close to the taps, so the water at the 'ring' remains hot. This is used in hotels etc to ensure hot water is reasonable available to individual rooms, even though the hot tank is distant. Let's assume we don't want to do this, it's non-trivial, and even less so to retro-fit.

So let's go with option (1); a source of hot water near the taps.

Option 1a) Instant HW heaters. I dislike these, Dribbly HW flow, and they remind me of portakabins.

Option 1b) Small immersion-based pressurised cylinders under the sink. These work well. They store a few litres ( and even more pints! )of HW under the sink, in a smallish unit. So long as you don't want to fill a bath from it, it's good ( hand-washing, etc. ) Advantages: Easy retrofit assuming cold supply is adequate; very close proximity: instant HW. Disadvantages: Lowish volume of stored HW.

Option 1c) Large immersion- or other- based tank, some further distance away. Advantages: Large volume of hot water ( if you want to fill a bath ); Reasonably close proximity. Disadvantages: bulky, complex retrofit.

Depending on what your needs are, the under-sink pressurised cylinders may be the simplest and most effective.

[NT]

I guess a small undersink job fed from your HW pipe would give you the best of both worlds. Instant HW for handwashing, plus an endless supply of hot for baths etc

NT

[Ron Lowe]

For the baths, I'd probably feed the existing HW through a solar panel in the roof and then through a 2KW instant heater. Then as a DIY solution to the stone-cold bath, take a 3KW element, wire it to a piece of flex, and throw it into the bath. Some silicone grease around the electrical connections ought to keep the smoke in.

Wear a full-body drysuit, or alternativly a body-bag to assist the emergency services.

[Roger Mills]

Assuming that you nead to heat an extra 7 pints (4 litres) of water by 55 degrees (from 5 to 60) each time you run the hot tap, the direct energy wasted is about a quarter of a kWh which - if using electricity at 10p per unit is about 2.5p. Allowing for inefficiencies, that may rise to 3 or 4 4p at the most. If you do this 4 times per day, you *could* waste 16p per day - or £58 per year - although the cost will be a lot less if using gas. Either way, the pay-back time on the cost of an additional installation will be quite a few years.

[David WE Roberts]

Another small combi close to the taps? Or just have the combi moved? We have stored hot water with a very long run of unlagged pipes and we can grow old and bitter waiting for the water to run hot, but we plan to replace everything with a combi close to the taps. In the long run this may be more cost effective for you than adding a second system and thus removing most of the point of having a combi in the first place. You used to be able to get wall mounted 'kettles' which held about a gallon and would heat on demand. My ex-workplace had a water heater which was supposed to replace the kettle but was plumbed in very badly and also had a bad taste to the water and so was not used, but you can get a water heater which will hold a few gallons and can be mounted on the wall and heated electrically. This is likely to be more cost effective than a conventional immersion tank which (AFAIK) is sized to fill a bath and takes up quite a lot of room.

Another thought - your combi is quite capable of acting as a system boiler and heating a hot water tank as well as the radiators. Perhaps you could have a hot water storage tank near to your taps which is heated on another circuit by the combi?

Oh, just move your sink nearer to the combi ;-)

Cheers

Dave R

[dennis]

If the tap is only used four times a day then running a smaller pipe will save a lot.

10 mm pipe would save about 50% and could possibly be done by drawing a plastic pipe through the existing one. Maybe even just inserting the pipe with the ends blocked off would work OK as it reduces the volume of the pipe. The flow would also decrease maybe to an unacceptable level. OTH it is a mains pressure system.

[John Rumm]

There is a variation on 1c; using an extra heating zone on the boiler to heat it rather than an immersion. However since it sounds like the gas in question here is LPG, the cost difference is not going to be as great as with electric Vs natural gas.

[Tim Lamb]

In message , Ron Lowe writes

I fitted option 1b and pleased swmbo:-)

After thoughts... I actually fitted ours in the hot supply (despite the instructions otherwise) because the water is softened and I thought it might help with lime scale. Running enough hot to rinse a tea cup does not fully heat up the pipe run. Worth insulating the connecting pipes as they bridge the cylinder insulation. A pressure relief valve is part of the kit and can usually be plumbed in to a spare spigot around the waste trap.

regards

[Roger Mills]

It would certainly solve the delay problem when you only want a small quantity of hot water. But it won't save you any money - and will probably cost *more* to run if all your kitchen water is then heated by on-peak electricity rather than by gas at one third of the price. And that's quite apart from the capital cost of the extra cylinder etc.

[Owain]

So rinse the teacup with a splash of hot water from the kettle.

Owain

[OG]

What are you more annoyed by? The waste of money or the waste of time ?

Despite all the widespread moans about the cost of energy, the actual 'cost' of the current setup seems to amount to not very much, maybe £200 a year.

However, standing at a cold tap for xx seconds/minutes/hours over a year is what really counts - assuming 90 seconds wasted 4 times a day, this comes to not much off the time spent in a working week (40 hours), so how much are you prepared to spend to get the annoyance sorted?

Talk to a plumber/gas CH installer - get a price, decide how much your wasted time each day, each week, each month, weach year is worth. If it's worth it, get it sorted

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Ron Lowe saying something like:

Or, to be really cheap, an old electric shower unit feeding an open spout.

[Bill Wright]

Thanks to all who have made sensible suggestions. There's the additional benefit of not having to wait for hot water. I might just do it.

Bill

[Dave Baker]

I've also run the calcs and agree the above if you were using electricity at

10p a k/Wh. However remember the heat lost from the pipes isn't actually wasted when you're heating the house anyway in winter. Using LPG as you are doing let's say it's really only costing about 3p per k/Wh so you're wasting 3p a day for 7 or 8 months of the year and the rest of the time it just helps heat the house. So that's about 7 quid a year. Not worth fussing over.

[Dave Plowman (News)]

Have you got gas in that area? A small multi point gas heater close to the tap would be ideal as you'll then get continuous hot water. They can be bought secondhand quite cheaply. There's no electric system that will provide this at a reasonable flow - takes too much current.

[NT]

shame no-one makes a pipe heating wire that wraps round the existing hot pipe and heats it to 60C thermostatically. Probably could be DIYed if you wanted.

NT

[Matty F]

Run the pipe near the tap through the neck and into the bottom of a large Thermos flask (vacuum flask) and take the water out from the top of the flask.

[Tim Lamb]

Huh!

I have to retrieve crocks from the washing up bowl and hide them in the dishwasher. Some domestic staff just love to get their hands in hot water.

regards