Hot water solutions (10m pipe run or seperate water heater)

[gsportgeorge]

Hi,

I need to plan how to get a hot (and cold) water supply to a small WC with sink and to a room that will eventually be the kitchen.

This isnt an issue right now except that I am re-fitting the bathroom and one option is to run the supply through this room, in which case I want to do it before plastering and tiling.

The WC is about 9m, and the Kitchen sink 10-11m (by the shortest routes) from a WB Combi and I am worried that this will mean a long delay before getting any hot water? Groundless fear or reasonable worry?

IF instead I run a cold supply only to the kitchen and use a little gas powered instantaneous water heater (there is a suitable external wall for the flu though it is over 600mm thick which might be an issue for some flues maybe?) then the WC is only 2 meters away (straight above).


IF I go with the instantaneous gas heater, what size/power would be reasonable and are they any good or am I setting myself up for a world of misery?

 

[gsportgeorge]

Does this sound reasonable?

I guestimate I am getting 15 l/min out of the existing hot taps (which have to fight through a maze of bodged lead, copper and plastic).

10m of 15mm copper has a volume of about 1.5 litres.

So adding 10m of run should only add 6 seconds to the wait for hot water... plus the time taken to heat the copper and get the water at a decent temperature...

At the moment the existing kitchen sink is only 4m from the boiler if the pipe ran a sensible way, but it runs a ludicrous way that is probably 8m or more. and it is really slow to come through warm (like 30 seconds plus)...

Any guidance would be much appreciated

 

[muggles]

I'd go with extending the run and waiting for the water, the instantaneous will take forever and a day to pay for itself against the cost of running water away.

 

[gsportgeorge]

Thanks for the reply Muggles, nice to get one...

Sounds reasonable but I am worried about the inconvenience of having to wait ages to get the hot water as much as the cost...

Would an electric one make more sense given that the pilot wouldnt have to be continually running and they are cheaper to buy and get installed?

Any idea what sort of size is sensible for a Kitchen sink with very small amounts used in a small handbasin in the WC now and again (probably not at the same time).

Thanks

 

[chrisjc]

I had essentially the same problem and after considering the options installed a 25 litre Santon electric storage heater in the utility room, run off-peak on a timeswitch. Much easier DIY proposition than a gas instantaneous. With a dishwasher for the main washing up the stored quantity was quite sufficient during the day but we did get fed up with the long wait (about 10m run to the kitchen, less in the utility room) and eventually moved the heater nearer the kitchen tap.

Somewhere I read an article that explains that the boundary layer of the water in the pipe is slowed by friction and so takes much longer than you expect to run hot.

Have also just installed a Triton 3kW instantaneous electric handwash unit in the WC in a different house. Less satisfactory in that you do not get the feel of a "proper" HW supply, and not much cheaper than the Santon either.

 

[gsportgeorge]

Thanks for the reply.

Should have said we will be using a dish washer for most of the washing-up so the requirement wont be that much.

We dont have storage heaters so I cant see it being worth going on a tarriff that has an off peak saving because they usually claw it all back during the day unless you can use a decent amount overnight. Also we dont really have the space for a big tank and 25l would surely go in no time?

I wonder if it would make sense to put an instantaneous eletcric heater on the "hot" supply? I assume that they are sort of thermostatic? That way the water would run hot fairly quickly, but when hot water started coming through from the combi it would turn off and save power?

Obviously if they arent thermostatic it would just mean scalding hot water...

 

[chrisjc]

Sorry, forgot to put this thread on watchlist.

I mislead you earlier, IIRC now the Santon was 45 litres, but it only ever ran cold when we were e.g. washing walls down with hot water. A significant part of the consumption must have waiting for it to run hot down the 10m pipe run so the closer the tap the better and 25l might well be OK for you.

If you are on an Economy 7 tariff you will of course also save money on the dishwasher and washing machine if you run them overnight, definitely worth doing. And your fridge & freezer will be on the night rate 7 hours in every 24. With all this we use about 25% on the night rate, it would be more if we had a washer/dryer which could do both in succession.

I don't think fitting an instantaneous heater on the h.w. supply is a good idea. They are not thermostatic as such, they have a fixed rating so the temperature just depends on flow rate. But they do have a ?non-resettable overtemperature switch so you run the risk of that tripping.

 

[gsportgeorge]

^^^ Thanks for the reply.

I think you are right, if the instantaneous electric heaters are not thermostatic then it definitely isnt a good idea.

Every tarriff I have ever looked at for economy 7 type use has had a substantially higher tarrif during the day, we also have an electric oven and hob (absolutely useless) and with small children the washing machine runs night and day anyway... so I doubt we would save ANY money on such a tarrif. Doing the equivilent of boiling 8 kettles each night almost certainly wouldnt be enough to make it worth while compared to an instantaneous one which would also save money if we didnt use the full 25l and be more convenient if we used more.... Then again I suppose there is no reason that the heater couldnt be filled from the hot feed off the combi...

My calculations suggest that to do 15l/min at a temp rise of 40degrees, would be 42kW... which seems a bit crazy...