Solutions for long hot water delay to kitchen.

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gzt

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#2713790 27-May-2021 13:29

Paul1977: @gzt total distance is (counting vertical inwall etc) would be around the 18m mark. 11.5m of this is in the roof cavity, the rest is in walls and under floor (conduit in concrete slab). I'm working on the assumtion it would only be feasible to replace the pipe in the ceiling cavity.

The pipe in the ceiling cavity is well worth insulating if it's do-able and anything else you can get to. The standard advice is nah doesnt make any difference because the wall/ceiling/whatever is already insulated. This is incorrect. It really irritates me it's not in the building plumbing code etc. Makes a big difference and requires less water to get a warm handwash or a hot sinkful.

mclean

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#2713820 27-May-2021 14:45

The pipe in the ceiling cavity is well worth insulating if it's do-able and anything else you can get to. The standard advice is nah doesnt make any difference because the wall/ceiling/whatever is already insulated. This is incorrect. It really irritates me it's not in the building plumbing code etc. Makes a big difference and requires less water to get a warm handwash or a hot sinkful.

That's an interesting one. If the sink is used say every 3-4 hours then even an insulated pipe will cool down to the extent that the water in it won't be hot enough. Once that happens, the insulation doesn't reduce the draw-off needed to get back to full hot.

While it's true the building code doesn't say hot water runs have to be insulated, it does recommend insulating the one to the kitchen. And it also limits the length of hot water pipe runs. For 20mm pipe the maximum length is 7m, or max 2 litres volume. In the O/P's case it's probably bad design.

Paul1977

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#2713859 27-May-2021 15:35

mclean:

While it's true the building code doesn't say hot water runs have to be insulated, it does recommend insulating the one to the kitchen. And it also limits the length of hot water pipe runs. For 20mm pipe the maximum length is 7m, or max 2 litres volume. In the O/P's case it's probably bad design.

I thought I'd read the max 2 litre figure somewhere. The house is only about 10 months old, so is this something that the plumbers legally had to do for it to be compliant? Or is it just a recommendation?

gzt

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#2714006 27-May-2021 16:58

mclean: That's an interesting one. If the sink is used say every 3-4 hours then even an insulated pipe will cool down to the extent that the water in it won't be hot enough. Once that happens, the insulation doesn't reduce the draw-off needed to get back to full hot.

Some of that insulation product is pretty darn good. Four hours later this can be enough to have a pleasant handwash immediately vs the alternative at this time of year freezing your hands and wasting water. It's a gain when it's easy.

Scott3

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#2714030 27-May-2021 17:39

neb:

Those small underbench cylinders tend to be horribly inefficient, unless they've drastically improved them in recent years. The Casa has the same problem, it's really an issue of having to push hot water from one end of the pipe to the other, displacing the existing cold water, for which the ad hoc solution here is to wait for something that needs a lot of cold water and use the initial runout for that, then use the hot water once the pipe has filled.

Bit of a harsh call to use the term "Horribly inefficient". Being restive electric, the actual heating is 100% efficient, and we have MEPS standards for standing heat loss. All the under-bench sized cylinders are requred to be below 1kWh of standing heat loss a day, and some examples beat 0.5kWh/ day.

For worst case 1kWh losses per day, and at 17c/kWh it would add $5.20 to OP's power bill, assuming the kitchen tap wasn't used. If we assumed the gas heater cost the same amount to run as electric (fair for LPG, but harsh for natrual gas), and water was free, 17L of wastage (waiting for hot water to turn up) per day would need to be avoided to break even from an energy perspective.

If it is a 0.5kWh real world loss, that would be $2.60 per month cost to have it standing, or 8.5L wastage per day saved to break even.

Obviously the under bench cylinder is a much more efficient outcome when it comes to not wasting water.

Would be interesting for OP to test how much water they are wasting every time they wait for hot to turn up. (fill up a bucket / jug etc, stopping to empty it and repeat if required, estimating the total amount of water run before the hot turns up...

https://www.energyrating.gov.au/sites/default/files/documents/Public-Product-Profile1_0.pdf

billgates

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#2714113 27-May-2021 21:10

Paul1977:

@billgates That doesn't look too bad, and price seems reasonable including install.

Did they plumb the input from a cold feed, or from a hot feed from the gas califont (so after if running for longer than a short period it refills with hot water)?

@Paul1977, the unit is connected to both hot and cold outlets under the scullery sink. There is a 3rd pipe connection off it as well which is going to an external condensation remover pipe.

Do whatever you want to do man.

mclean

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#2714376 28-May-2021 10:34

Paul1977: I thought I'd read the max 2 litre figure somewhere. The house is only about 10 months old, so is this something that the plumbers legally had to do for it to be compliant? Or is it just a recommendation?

Probably legally required, yes. It comes under the energy efficiency Acceptable Solution NZBC H1/AS1, which you can read here:

https://www.building.govt.nz/assets/Uploads/building-code-compliance/h1-energy-efficiency/asvm/h1-energy-efficiency-4th-edition-amendment-4.pdf

Clause 5.0 of that Acceptable Solution calls NZS 4305:1996, which is here:

https://www.standards.govt.nz/shop/nzs-43051996

You can download both of those free.

Convoluted, but the Building Code is like that.

There are alternative ways of complying with the building code. But that would be practically unheard of for a house, and I can't think of any other standard that would allow what you describe.

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Paul1977

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#2714503 28-May-2021 12:38

mclean:

Probably legally required, yes. It comes under the energy efficiency Acceptable Solution NZBC H1/AS1, which you can read here:

https://www.building.govt.nz/assets/Uploads/building-code-compliance/h1-energy-efficiency/asvm/h1-energy-efficiency-4th-edition-amendment-4.pdf

Clause 5.0 of that Acceptable Solution calls NZS 4305:1996, which is here:

https://www.standards.govt.nz/shop/nzs-43051996

You can download both of those free.

Convoluted, but the Building Code is like that.

There are alternative ways of complying with the building code. But that would be practically unheard of for a house, and I can't think of any other standard that would allow what you describe.

@mclean thanks for that.

Maybe they used narrower pipe to the kitchen? I've been assuming it was done like the other pipes I can more easily see, but perhaps it wasn't for the kitchen because of these requirements. I guess I need to squeeze myself up there to have a look.

If it's not right I guess I can kick up a stink when it's time for the 12 month maintenance check in a couple of months. But you think the pre-pipe inspection would flagged it if it was not compliant?

Are the diameter measurements of the pipe internal or external (e.g. is a 200mm pipe 20mm internally or more like 22mm externally?)? If the size isn't written in the pipe (or it's lagged and I can read it) I guess I'll need to use calipers to measure the external diameter.

mclean

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#2714593 28-May-2021 14:11

Paul1977:..But you think the pre-pipe inspection would flagged it if it was not compliant?

Very unlikely, unless the inspector was a plumbing guru, and even then unlikely. Going to the council and claiming the CCC was invalid would be an enormous waste of time, which council's can afford, but you can't.

You might try negotiating with the plumber for a discount on the cost of a new under-bench heater to fix the problem.

Paul1977

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#2714708 28-May-2021 16:14

mclean:

Paul1977:..But you think the pre-pipe inspection would flagged it if it was not compliant?

Very unlikely, unless the inspector was a plumbing guru, and even then unlikely. Going to the council and claiming the CCC was invalid would be an enormous waste of time, which council's can afford, but you can't.

You might try negotiating with the plumber for a discount on the cost of a new under-bench heater to fix the problem.

Oh well, I'll get up there and determine what the pipes actually are before looking at options for improving it. Thanks for the help.

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