Hot Water (Theorising)

[John]

Would it contribute much to water saving if hot water pipes were really well lagged so that it isn't so necessary to draw off cold water (dead leg) before it starts to run hot? Are there regulations in place now as my pipes (18 year old house) under the upstairs floors are not lagged.

Also - at what size of house might it become economical to install a sort of pumped hot water ring main so that no tap is more than a few feet from a circulating flow of hot water? Is this done? I guess it could be simple to have a timer controlled low energy pump - along with well insulated pipes.

Any thoughts?

[Aidan]

Yes, been in the water regulations for years, to prevent waste. There's maximum lengths specified for uninsulated water pipes.

If your budget will stretch to it and you want instant hot water....... Done as routine commercially, partly also to prevent legionella proliferating in tepid water. Grundfos market a pump aimed at the domestic market. You shouldn't use a standard CH pump, the innards will corrode.

[David Hansen]

On Tue, 14 Mar 2006 11:26:12 GMT someone who may be "John" wrote this:-

A large one. However, even in a large house it will often be better to provide local water heating for groups of outlets.

Even with well insulated pipes such circulation represents a fair heat loss.

[Harry Bloomfield]

John has brought this to us :

That would depend upon useage. Even the best insulation will only keep the water in the pipes hot for so long.

[Ian Stirling]

It can be a fair time. IIRC, 15mm pipe, with 15mm of polystyrene insulation (what I did the numbers on), starting at 60C above ambient will drop 10C in the first 6 mins or so. (roughly). The question then becomes how often do you draw off a small quantity of water more than 5, but less than 20 mins.

[Ed Sirett]

It is always a good idea to insulate hot pipes. Pipes have to be insulated within 1m of the cylinder (IIRC) however they are easily acessible in the airing cupboard and this is then simply a matter of best practice.

Those much large than the average.

Yes.

I guess it could be simple to

A bronze pump (5x the cost of a cast iron one) on the lowest setting. Timers and/or PIRs can be used to reduce the pumping time. Insulation is essential.

The larger unvented cylinders and thermal stores will have these.

[Mary Fisher]

Only if the cylinder is in the airing cupboard ...

Mary

[Ed Sirett]

What I meant is that the cylinder is usually in an accessible space and the pipework is similarly accessible.

[Mary Fisher]

I'm not challenging you, Ed, I wouldn't. I respect you too much.

But you did mention the airing cupboard and many cylinders aren't in them these days. Modern cylinders are far too big, especially when properly insulated, to fit into original 'airing' cupboards.

That said, your point about insulating hot waterpipes is absolutely sterling advice, wherever they are. If they're in an inaccessible place it's worth making the effort to find an innovative way of insulating - not necessarily by pipe lagging.

Spouse used pu foam in a difficult top corner where there were several pipes and it would have been impossible to lag each one individually. The foam was smoothed and painted like the rest of the cupboard (the airing cupboard!) and is only noticable if looked for.

Mary