Running hot water about 16m, options?

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#2282753 24-Jul-2019 11:52

mclean:

It's not just the delay and water wastage to consider - it also wastes energy. If you need to draw off say 10 litres of water before the hot comes through that's 10 litres of HOT water wasted, not cold water.

The building code has an energy efficiency rule for this but it only applies to kitchen outlets. The maximum amount of water you can have in the pipe between the water heater and a kitchen tap is 2 litres.

Circulating systems are pretty much standard in commercial buildings but I've never seen one in a house. A typical hot water circulator draws about 30W so there's that. You can get them with built-in clock control.

How long has that been in the building code? Our 2001 built house has miles between the infinity heater and the kitchen sink. It takes the best part of a minute for it to run hot, probably 5-8 litres.

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#2282759 24-Jul-2019 12:06

MrAmerica: You sure the building code specifies to the kitchen? Plumber said its anywhere in the house, ie I think pipe to the bathroom can be obly 15mm due to this?

It's NZS 4305 clause 3.2 (called by NZBC Acceptable Solution H1/AS1). You can download the standard for free now. But I would certainly recommend the same for bathrooms and don't over-size the pipe.

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#2282762 24-Jul-2019 12:09

BlueShift: How long has that been in the building code? Our 2001 built house has miles between the infinity heater and the kitchen sink. It takes the best part of a minute for it to run hot, probably 5-8 litres.

I'm not sure about that - the oldest copy we have is 2007 and it was in then.

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#2282830 24-Jul-2019 14:34

mclean:
MrAmerica: You sure the building code specifies to the kitchen? Plumber said its anywhere in the house, ie I think pipe to the bathroom can be obly 15mm due to this?

It's NZS 4305 clause 3.2 (called by NZBC Acceptable Solution H1/AS1). You can download the standard for free now. But I would certainly recommend the same for bathrooms and don't over-size the pipe.

Thanks, I will see if I can track that down and have a read.

Zeon

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#2282865 24-Jul-2019 15:20

trig42:

From my back of the envelope calculations, 16m of 15mm pipe would hold about 11 litres of water. At mains pressure (25L per minute according to watercare) that should take less than 30 seconds to be running hot.

Volume = πr2h
= π×0.00752×16
= 0.0009π
= 0.0028274333882308 meters3

I.e 2.8L of water.

We have I would guess 15m-20m between our hot water tank and furthest faucet including probably 7m outdoor at 20mm before 15mm indoor. Our flow rate if we really let the tap rip is 90L per minute so we can get hot water pretty quick if we want it.

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trig42

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#2282883 24-Jul-2019 15:51

Zeon:

trig42:

From my back of the envelope calculations, 16m of 15mm pipe would hold about 11 litres of water. At mains pressure (25L per minute according to watercare) that should take less than 30 seconds to be running hot.

Volume = πr2h
= π×0.00752×16
= 0.0009π
= 0.0028274333882308 meters3

I.e 2.8L of water.

We have I would guess 15m-20m between our hot water tank and furthest faucet including probably 7m outdoor at 20mm before 15mm indoor. Our flow rate if we really let the tap rip is 90L per minute so we can get hot water pretty quick if we want it.

Ah, yes, you are right. My back of the envelope did not halve the diameter to get the radius. eejit.

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mclean

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#2282889 24-Jul-2019 15:57

Zeon:.. I.e 2.8L of water.

We have I would guess 15m-20m between our hot water tank and furthest faucet including probably 7m outdoor at 20mm before 15mm indoor. Our flow rate if we really let the tap rip is 90L per minute so we can get hot water pretty quick if we want it.

That's pretty good.

Energy-wise, running 2.8 litres out of a hot tap is about equivalent to filling a kettle, boiling it, and tipping it down the drain. That's BEFORE you get the hot water you want.

Zeon

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#2282938 24-Jul-2019 16:17

mclean:

Zeon:.. I.e 2.8L of water.

We have I would guess 15m-20m between our hot water tank and furthest faucet including probably 7m outdoor at 20mm before 15mm indoor. Our flow rate if we really let the tap rip is 90L per minute so we can get hot water pretty quick if we want it.

That's pretty good.

Energy-wise, running 2.8 litres out of a hot tap is about equivalent to filling a kettle, boiling it, and tipping it down the drain. That's BEFORE you get the hot water you want.

Yea I get that. So we have converted the area where the water tank used to be to a minor dwelling so there wasn't a place for it inside anymore. Plus have connected a seperate outbuilding up to the same tank too. With 2 kitchens and multiple bathrooms feeding from the same outdoor pipe, it should be pretty active and keep the water inside warm with enough insulation. Parts of the 20mm pipe are feeding 3x showers, 5x hand basins, 2x kitchen sinks, 2x washing machines and 2x dishwashers so it should be pretty active. it's also well positioned now for solar water heating which I want to do perhaps in the coming year or 2.

Seriously, all of these standards and regulations are too much. Like considering the distance to the water heater in the standard - what happens with solar water heating when its far from the user? I want to put the solar water heaters on a different building to where the primary users are with the hot water tank in between. In such a case is the water heater the sun so 150 million KM away?

It seems like all these regulations are in place because everyone became too cheapskate to want to build quality. As long as its safe, then should be up to the person building and if they can't sell it because its poor quality than that is their problem....

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#2282942 24-Jul-2019 16:23

mclean:

Zeon:.. I.e 2.8L of water.

We have I would guess 15m-20m between our hot water tank and furthest faucet including probably 7m outdoor at 20mm before 15mm indoor. Our flow rate if we really let the tap rip is 90L per minute so we can get hot water pretty quick if we want it.

That's pretty good.

Energy-wise, running 2.8 litres out of a hot tap is about equivalent to filling a kettle, boiling it, and tipping it down the drain. That's BEFORE you get the hot water you want.

But at what cost would the solution be to avoid this wasted heating?

I totally get why you'd want to avoid this - from an on-going financial, environmental and sanity-preserving perspective - if it was a regularly-used space such as a main bathroom or kitchen (as in my in-laws' house, as mentioned earlier).

But, I'm betting that for the OP, as it was for us in a very similar scenario I outlined near the start of the thread, cost of installing a second heating system would far outweigh the benefits, given in both these cases the bathroom isn't expected to get much use.

mclean

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#2282967 24-Jul-2019 16:50

jonathan18: ...I totally get why you'd want to avoid this - from an on-going financial, environmental and sanity-preserving perspective - if it was a regularly-used space such as a main bathroom or kitchen (as in my in-laws' house, as mentioned earlier).

But, I'm betting that for the OP, as it was for us in a very similar scenario I outlined near the start of the thread, cost of installing a second heating system would far outweigh the benefits, given in both these cases the bathroom isn't expected to get much use.

As I said, the rule applies only to kitchen taps. For bathrooms you can use your own judgement. Whether the rule applies to solar heated systems isn't clear - I'm sure it wasn't intended to and I don't think any Council would pull you up on it.

mattwnz

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#2283031 24-Jul-2019 19:22

mclean:

MrAmerica: You sure the building code specifies to the kitchen? Plumber said its anywhere in the house, ie I think pipe to the bathroom can be obly 15mm due to this?

It's NZS 4305 clause 3.2 (called by NZBC Acceptable Solution H1/AS1). You can download the standard for free now. But I would certainly recommend the same for bathrooms and don't over-size the pipe.

I wonder how many houses that are built today aren't within that max distance , I suspect a lot. Prior to the last few weeks these standards weren't readily available unless people paid for them.

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Kickinbac

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#2283049 24-Jul-2019 20:00

For the OP.
I’ve seen on american websites systems that use a recirculating hot water pump to send cold water in the plumbing line back to the hot water heater, via the cold water or a dedicated return line, while simultaneously bringing hot water to all fixtures on that plumbing line. The system had a push button that switched the pump on and a temperature sensor that turned the pump off when the hot water arrived. Some versions use an occupancy sensor so if someone went into the bathroom, the pump switched on automatically.

MrAmerica

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#2283829 26-Jul-2019 08:21

Kickinbac: For the OP.
I’ve seen on american websites systems that use a recirculating hot water pump to send cold water in the plumbing line back to the hot water heater, via the cold water or a dedicated return line, while simultaneously bringing hot water to all fixtures on that plumbing line. The system had a push button that switched the pump on and a temperature sensor that turned the pump off when the hot water arrived. Some versions use an occupancy sensor so if someone went into the bathroom, the pump switched on automatically.

Yes thats what I was looking at. But I think considering its only going to see use with visitors, kids staying etc its probably not worth the hassle. Also we are going to install solar so costs for hot water on average will be bugger all anyway.

bfginger

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#2284450 26-Jul-2019 23:04

Don't install those "water saving" taps any distance from the cylinder. They run so slowly it takes forever for the hot water to arrive. Total waste of time and energy.

Make sure to insulate the full length of the hot water pipes. It's very cheap to do.

Kickinbac

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#2284453 26-Jul-2019 23:33

Insulating the pipes may have little effect if the bathroom is only used occasionally. The water will sit in the pipe and just cool slower.

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