Lagging boiler hot water delivery/supply

[AnthonyL]

Should the cold water supply and the hot water delivery be wrapped up together?

I'm working in the mainly boarded loft (bungalow) and have uncovered some of the boxing/platform under which the pipes run. The boxing sits about 5" above the joists and is insulated.

The supply and delivery 1/2" pipes run about 20m from the front of the house to the back and are next to eachother. The lagging, felt I think, seems to be wrapped around the outside of the pipes rather than around the pipes individually.

The hot water takes a long time to come through to the kitchen and I wonder if it is spending heat warming the cold water next to it. Whilst I can see some advantage in effectively pre-heating if the demand is for a lot of water, it would seem to be counter productive if just a small amount of hot water is needed.

[Brian Gaff]

More likely that the water in the pipe will always be cold unless its been run off. I suppose the idea of warming the cold a bit would make some difference but maybe it was done to stop it freezing? Brian

[Theo]

I suspect it's probably been lagged for frost protection - ie keep the cold out of both pipes - rather than efficiency. That does nothing the other 99% of the year - in fact likely makes it worse. Better to individually insulate the pipes so they are frost protected and the hot water stays hot.

How much space is there between the two pipes? Enough to squeeze in some foam insulation around each pipe?

This stuff is good (also good at noise dampening):

while this is cheaper but better than nothing: probably want the pre-slit version which I can't seem to find on that site)

General rule of thumb is to install the pipe diameter's thickness of insulation, but often there's not space for that so you have to compromise. The nitrile Armaflex is self adhesive so just slips around the pipe and sticks to itself, while the polyethylene needs exterior fixings (eg tape or cable ties).

Theo

[Martin Brown]

In an ideal world no. But the main effect of having the pipes too close together is that after running hot water you end up with a cold pipe that is full of lukewarm water for some time afterwards.

A bit of insulation between them would help keep your cold water pipe colder. Unless it bothers you I wouldn't bother disturbing them unless you are already doing some other work up there.

No. That is just the distance the water has to flow before it fills the long pipe with hot water. There are some losses to the cold copper pipe it is in but losses to the adjacent pipe assuming it is not in direct contact with the hot pipe will be on the timescale of 10s of minutes.

Hotels have a circulating loop for hot water with short drop legs from the main pipe loop. Much more lossy but near instant hot water.

[Theo]

I think the goal here would be to insulate the hot pipe so it stays hot. Then more of the time you're running hot water that's in the pipe, rather than waiting for hot water to come all the way from the far end. Where it loses heat to is irrelevant, just that you have to run all that lukewarm water out before it turns out. If the run is long, that time can be significant (and water wasted significant too).

A second thing is if you want cold water for eg drinking water, and that causes you to run the tap until it goes cold. In that case, insulating the cold will keep that colder. If you aren't so bothered by it being cold (eg in a bathroom) then you might decide not to insulate the cold.

As long as there is some insulation around both pipes they'll be frost protected - doesn't matter if it's together or separately.

That's also because their pipe run could be hundreds of metres long, and if you turned on the tap or shower at 3am you could have to run it for quite a long time to get hot water from the tank.

Theo

[AnthonyL]

Not fully sure I understand "10s of minutes"

Thanks Theo and Martin.

I've had a closer look - see

Seems as if the delivery pipe is 1/2" (and earthed) and the return pipe presumably 3/4" which I calcuate to be 5.7L. That's over a gallon before any warmth comes through.

As can be seen the pipes are close together but not touching, and there are two spirals of felt wrapping. It cannot be cost effective to try and replace the approx 15m length I can more or less readily get to.

Just trying to improve the loft insulation brings home how expensive and time consuming the exercise is when not done as part of original build.

At the top of the picture can be seen the original loose insulation which is going to get rolls of 200mm insulation laid over. I think any electrics should as far as possible be over the insulation.

Not worthwhile though for just two retired folk in a bungalow, as appealing as the idea is.

[AnthonyL]

The cold water feed is just to the boiler and utility room. As we are quite sparse with running the hot water back to the kitchen I don't think we encounter cold water that is not cold, additionally the kitchen cold water tap is directly above the water meter.

[Theo]

If you wanted to improve things, what I'd think about is getting some plastic barrier pipe (PEX or polybutylene; PB is more flexible), putting some Armaflex insulation on it (the full-round stuff can be slipped over the cut end of the new pipe avoiding having to seal along each length), and then splicing it into the existing heating pipe at each end. Then your old pipe run carries just the cold and an empty old hot pipe, with sufficient lagging for frost purposes. And now you have a well insulated new hot water run.

Because it's flexible it's easier to run wherever you want without having to disturb too much other stuff.

Theo

[Andrew]

If this is a Combi boiler then it is in the wrong place. Ideally it should be as close to the point of use as possible, and normally in the kitchen, with the bathroom immediately above.

Some makes also have a (not very) eco setting whereby it learns your usage patterns and keeps it internal heat exchanger hot.

Separate lagging might be a good idea if it is a combi and if your mains pressure is good enough even replacing a long run of hot 15mm pipe to the kitchen (with a tee junction for the bathroom) with 2 separate 10mm hot water feeds to the kitchen and bathroom would reduce the delay.

[Martin Brown]

That's about how long it takes for heat transfer through air from one pipe to the other. Your pipe run looks a bit close together to me and with old style wrap around lagging. Glass fibre? Wear a dust mask and gloves it is itchy as hell if you touch it and much worse to breathe!

I'd say it was more tedious and unpleasant than anything else. If you can find it get the stuff that is wrapped in a thin foil on one side bag to minimise your contact even with the modern rockwool. Shiny side up.

The other alternative is an under sink water heater of the flash boiler type. Tend to be electric which isn't ideal given energy prices now!

[AnthonyL]

Well you are right but - it is placed in an extension which is the utility room. The original build was to have a system boiler in the loft as you suggest. But the utility room has the main shower so plenty of hot water very quickly delivered.

Not ours. Baxi 105HE but I have learnt that as SMART isn't always smart neither is ECO always eco.

The main hot water usage is in the kitchen, apart from the shower which is well served. I'm not particular bothered about the delay when filling the bath as it is only used a couple of times a year and the wastage is only a small percentage of the usage.

[AnthonyL]

Got it.

Pretty sure it is felt, not irritating to touch. The insulation underneath however is as are also the insulation rolls I've already bought to spread over the loose insulation in the few feet up to the eaves.

On that issue I've read that the insulation shouldn't go right to the edge so as to allow ventilation. However as best I can see we have soffits and facias (just been replaced with PVC) and there are no gaps. We had half a dozen roof tiles replaced with vents as there were signs of interstitial ventilation when we bought the house 6 years ago and that problem has gone.

I've already bought a few rolls of

It seems to have come pre-scored but also cuts nicely with a bread (or ice - not sure) knife.

Yes that's been the dilema all along, use cheaper gas inefficently or more expensive electricity, plus cost of install. Being well into my

70's I'll likely never see a ROI.

[Tricky Dicky]

I think you will find the insulation is more to prevent freezing than preserve heat in the hot water pipe. If you are bothered about the hot pipe heating the cold, separate them even a couple of centimetres will do and some packers in between. Cover the lot with the loft insulation. The “hot” pipe will only be hot whilst a tap is flowing the rest of the time it will be cooling and eventually reach the same temp. As the cold pipe. I think you are overthinking the situation too much and myself I would leave well alone apart from covering both pipes with the loft insulation. As for the pipe run and waiting a few minutes for hot water to reach the kitchen tap there is little you can do as increasing the pipe diameter will not solve the 20m run as it depends on the rate at which the boiler can heat the water.

Richard