Hot water goes cold in the pipes: what to do

[silentC]

This is a common problem in most houses I guess, but some are worse than others. Anyway, having just moved into a house that is on rainwater, I'm interested in finding a solution for the water that is wasted when you run the cold stuff out of the hot pipes if it hasn't been used for awhile. At this time of the year it goes cold quick. We have one bathroom that is a fair distance from the heater and it takes at least one basin-full of water to get any hot through.

There are 3 options to pursue. The first is lagging. This is OK as a short term solution - it keeps the water in the pipes hot longer but it will eventually go cold. So it's fine in the kitchen, where you might want hot water periodically over a fairly short space of time. There's still the sink-full you lose the first time you turn on the hot tap.

The second option is the circulation pump idea. We tried this once at a house that had a twin element, with the top one on standard rate. We found that energy costs went way up because the cooler water being returned to the heater caused the top element to come on all the time. When we disabled the top element, we were running out of hot water because the circulation of water through the system was creating a lot of heat loss on the round trip and so the overall temp in the cylinder dropped, and because it was on off-peak, it wasn't heating up again. This solution saves water but costs more to run. You also have the overhead of the circulation pump.

The third is the thermostatic valve, which diverts the cold water to somewhere else until it reaches a preset temp. You can either store it in a bladder tank to be reused next time you turn on the cold tap, or you can divert it to your rainwater tank. Probably the only downside to this one is that you turn on the hot tap and nothing happens for awhile. They tell me you get used to it, but I can imagine visitors washing their hands, only to find no water coming out. So what do they do? Turn the tap more... and more... and then out it comes like Niagra Falls and hot water all over their nice clean frock.

I have been wondering if a combination of all three would work. Say you had one of the thermo valves in the hotwater line near it's farthest point, with the cold water return piped back to the hot water cylinder. You set the temp so that it's a fair bit below normal hot temp. As the water in the pipes cools, the thermostat opens and the water circulates back to the cylinder. When the hot reaches the thermostat, it closes the divert valve again. Sort of similar to the circulation pump but it only happens periodically. Rather than trying to keep the water in the pipes at normal temp, it keeps it a bit cooler, but not cold. There's less time to wait for warm water to come through because it's already part way there. Lagging helps to keep it warmer. Then maybe a thermo valve set up on the kitchen sink and the vanities.

The valves are about $130 each. To install one in the line on the upstream side of a tap, you also need a diaphragm valve which enables the setup to work when the pressure drops (when a hot tap is turned on downstream). Don't know how much they are, but I'd guess around the same amount.

So, does anyone have any experience to contribute?

[Two-Words]

Like this Daz ?

http://www.abc.net.au/newinventors/txt/s1389495.htm

[silentC]

Yep, already spoke to him It saves the water, no question. Just looking to see if there's also a way of reducing the wait! Impatient soul I am. Whoever you are.

[echnidna]

Yep, already spoke to him It saves the water, no question. Just looking to see if there's also a way of reducing the wait! Impatient soul I am. Whoever you are.

He's Two Words from Wagga Wagga via Melbourne - Outer East Foothills

[silentC]

Yeah, but does he know anything about hot water? That's what I want to know...

[echnidna]

I thought he was used to being in hot water

[echnidna]

Another solution for the outlet thats a long way from the HWS is put an instantaneous hws very close to it. You'd need to compare costs to see which is most cost effective.

[bitingmidge]

Well two words aside, I'm too late to help, but post the following in the interests of anyone in the future planning a renovation/house.

1) Lag every inch (25mm's) of hot water pipe. The more the better, even if you have plastic plumbing pipes.

2) Locate the Hot Water Unit as close to the sink as you can, I like to have less than 2m of pipe at that point. This is because the kitchen consumes the most number of small squirts of hot water, so you are wasting a lot less.

3) Plumb the hot water in a continuous "ring main" emptying back into the unit. (This sometimes needs the plumber to do some homework to get it to work correctly.) Convection should keep the water moving continuously, and if it is lagged correctly it should lose only a minimal amount of heat. In theory the energy loss should be less than the bucket you are sacrificing each time you turn on the tap currently.

Sorry I didn't think to post that before you started. Doesn't everybody do this stuff as a matter of course?

Cheers,

P

[Barry_White]

Silent

Because of where I live when I built the house I used lagged pipe on both the cold water and the hot water, this was mainly to prevent pipes freezing in winter.

The hot water does not stay hot for very long even in the lagged pipes and I would guess this is because of the low volume of water in the pipe.

Like Bob says an instantaneous heater in close proxcimity to the tap that you are using constantly.

[silentC]

Well, you see Midge, I was planning on putting the HWS directly under the kitchen but changed my mind. I'm fickle like that. I decided I wanted it close to the ensuite so I don't have to wait for hot water when shaving.

It's probably about 5 metres away but I'll have to have a look at how the plumbing was done. Maybe it goes via the next door neighbour's spa. Anyway, the plumber is a resident and we focused on getting in with the luxury of fixing things like this later.

Lagging: well, yes and that has been done mostly, although there are spots that we haven't done yet. Another rainy day job. We used that black foam stuff, probably there are better things on the market.

The 'ring main' idea is a new one on me. I don't see the real difference from the other ideas though - you are still going to lose some heat, no matter how good your lagging is and you are returning colder water to the cylinder which then needs to be reheated - which wont happen until off peak cuts in. Maybe not such a problem in QLD as it is here. I liked my valve idea because it limits the round trip a bit. Do you lose any heat through kinetic energy?

[silentC]

The old man wanted to put a small instant heater in just outside his kitchen window. I saw that as a potential extra overhead because of the running cost. I suppose it's a question of whether that balances out against the losses involved in having to heat up a bit more water each night because of the hot water that went cold in the pipe. It's probably marginal.

I suppose our main focus is on saving water and energy is secondary.

[dazzler]

hey silent

what about moving the hot water heater next to the bath and not run hot water to the kitchen at all.

then get one of those instant hot water systems they have in kitchenettes in offices.

Almost instant in both rooms

cheers

dazzzler

[silentC]

If gas was a bit cheaper here, then a couple of instantaneous jobbies would have been good. Unfortunately, although they are the worst for energy efficiency, the big electric storage job is the cheapest to run here in hicksville.

Oh well, no comments on my circulating with the valve idea. Guess I'll just have to try it. Stay tuned.

[dazzler]

Hi silent

i wasnt thinking of the expensive gas systems for the kitchen. Just one of the electric wall mounted ones that office workers get hot water for a coffee or tea.

good luck

dazzler

[bitingmidge]

i wasnt thinking of the expensive gas systems for the kitchen. Just one of the electric wall mounted ones that office workers get hot water for a coffee or tea.

http://www.spec-net.com.au/extras/zipindustries3.html

But it would be cheaper to drive to town everytime you wanted a cuppa. Boy these things cost!