Instant vs Gas cylinder hot water

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cldlr76

289 posts

Ultimate Geek

#106226 19-Jul-2012 17:34

Hi,

Has anyone swapped a gas hot water cylinder to an instant hot water system, and if so what affect did it have on your power bill.

People have said to me that you end up using more hot water with the instant systems because people stand in the shower longer not worried about running out of hot water but with the bathroom controllers you can stop that by setting the volume of water used for a shower.

Thanks

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#658626 19-Jul-2012 18:08

A bathroom designer I talked to recently said he bought a house with one and didn't like them. Time to start supplying hot water and time to come up to heat if another tap's turned on were the main things.

astrae

268 posts

Ultimate Geek

#658630 19-Jul-2012 18:16

We have an Infinity Instant Hot water system and we love it. I don't quite understand your post; are you going from Electric to gas or looking at Gas Cylinder to Instant because going from gas to gas isn't going to effect your powerbill????

We went from Electric to Instant gas and took about $60 a month off our power bill. We love the system and have no problems with it at all. Instant is good because when you aren't using it, it sits idle. A gas hot water cylinder works in a similar way to electric so it is constantly keeping the water hot.

We are on bottled gas as mains supply isn't available in our street. A 40KG bottle lasts us about 2-3 months and costs $107.

cldlr76

289 posts

Ultimate Geek

#658648 19-Jul-2012 19:14

Sorry, yes I mean gas bill, we have mains gas which is on the same bill as the power, so commonly just refer to it as the power bill.

When I spoke to the gas fitter when we did our kitchen he said we would have to replace the existing gas line to the hot water cylinder with a bigger diameter one as the instant systems use a lot more juice to instantly heat the water. So I'm not sure having a tank constantly heating, but with a lower gas flow would be much worse than only heating the water you use but at a higher gas flow.

Thats interesting about the time it takes to get hot water to a tap, obviously instant doesnt really mean instant.

mattwnz

20164 posts

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#658649 19-Jul-2012 19:17

cldlr76: Sorry, ?yes I mean gas bill, ?we have mains gas which is on the same bill as the power, so commonly just refer to it as the power bill.

When I spoke to the gas fitter when we did our kitchen he said we would have to replace the existing gas line to the hot water cylinder with a bigger diameter one as the instant systems use a lot more juice to instantly heat the water. ?So I'm not sure having a tank constantly heating, but with a lower gas flow would be much worse than only heating the water you use but at a higher gas flow. ?

Thats interesting about the time it takes to get hot water to a tap, ?obviously instant doesnt really mean instant. ?

I was told it uses more power than a gas hot water cylinder. But I think it also depends on how many people are in your house. If there s just one person, and you have got a big cylinder that is being heated the entire day, then an infinity unit should be cheaper.

astrae

268 posts

Ultimate Geek

#658651 19-Jul-2012 19:19

Ours is instant. 4-5 seconds for the bathroom taps which is about right for the distance of the pipes.

Kitchen is still little longer as its further away.

Our system is 2yrs old.

scuwp

3885 posts

Uber Geek

#658652 19-Jul-2012 19:20

Yes the instant may use more energy when its running, but it is using next to zero energy when its not being used. I have always understood that a major cost in water heating usage was not the use of it but storing it for extended periods. The instant systems of course stop that happening.

It depends on the install location as to how long it takes to get to the tap, no different to the storage system. Long distance away = long time for hot water to get to tap. Personally I have not noticed any unacceptable delay.

I have had instant (Infinity et al.) for a very long time, NO WAY would I go back to storing hot water.

Just my 2 cents...

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davidcole

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#658671 19-Jul-2012 20:13

I thought rinnai had a new system where it can keep the water in the pipes warm...So like a hot water cylinder it's using a big more gas (or power?) when idle but still much less that keeping a cylinder warm.

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timmmay

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#658675 19-Jul-2012 20:20

I was told modern cylinders are so well insulated they lose very little heat, that it was mostly lost from the pipes and fittings.

I'm about to put a cylinder up in my ceiling cavity, which obviously gets very cold in winter. The plumbing firm's planning on putting a standard cylinder up there. Any suggestions anyone? There are outdoor cylinders but that seems like overkill.

Niel

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#658703 19-Jul-2012 21:16

Yes, modern cylinders are very well insulated to the point that people install heaters in their linen cupboard because the cylinder does not warm up the space to stop mould growing. On our cylinder it is only the copper pipe coming out of the cylinder where you can feel any heat.

In South Africa the normal place for a cylinder is in the ceiling, there is absolutely nothing abnormal about that. But the humidity is low enough that you just don't get mould so there is no need to warm up the linen cupboard. Biggest issue is when you have a significant leak and the drain pipe on the pan under the cylinder is not large enough to cope or was not hooked up in the first place, but NZ has strict standards and accountability.

Electric cylinders do not constantly use power, it only uses power to recover from heat loss which is not much in a modern cylinder.

But what I'd get next time is a heat pump electric cylinder and put a diverter on the exhaust. In winter the exhaust would go outside, in summer it would go inside. So in summer the waste cold air would cool the house.

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timmmay

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#658706 19-Jul-2012 21:24

Thanks Niel, makes sense :) Heat pump hot water isn't economical yet unless you use use a heap of hot water, according to consumer.

stuzzo

534 posts

Ultimate Geek

#658717 19-Jul-2012 21:45

When the water stops flowing in your hot water pipes, that stagnant water then acts as an insulator to prevent much further heat loss from the HWC. Often the outlet pipe bends down once it leaves the top of the cylinder which is particularly effective at stopping heat loss.

You will lose the heat from the water run into the pipes as they cool. Further insulating of all the pipes is only really effective if water is used frquently.

mattwnz

20164 posts

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#658719 19-Jul-2012 21:50

timmmay: Thanks Niel, makes sense :) Heat pump hot water isn't economical yet unless you use use a heap of hot water, according to consumer.

They are often used for underfloor heating, heating the water for the pipes.

Handle9

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#658736 19-Jul-2012 22:14

Power wise instant gas hot water heaters are very good. There are two of us in the house with a very high flow rate shower and the only thing we have on gas currently is hot water. Our bill is about $45 a month of which $30 is connection charges. They use LOTS of gas when running but they don't run for all that long compared to a storage system.

There are some issues with instant hot water heaters. The first as some people have mentioned is the dead leg. There is no latent heat to keep you how water pipes warm so if your main uses (bathroom and kitchen) are a long way away from the heater then you have to purge quite a bit of water before you get hot water. Also if you don't have the shower as the first branch you get temperature fluctuations when you turn on a tap. Depends on your house and your plumber should be able to advise you. If you design the hot water system for instant hot water you can get better performance but you are looking at a retrofit.

The other issue which had is you need a high capacity gas feed. Our mains feed from the meter was one of the old "free" connections and had been undersized. Effectively every pipe size was smaller than it should have been - the main should have been 25mm and was 20mm, the branch feeds should have been 20mm and were 15mm etc. What happened the hotwater heater starved of gas and we got fluctuations of temperature without any other taps on. Along with a 10 year old heater it made having a shower a bit of Russian roulette - hot/cold/hot/cold.

If this is the case for you it can be a very expensive exercise to get it fixed. I got my main replaced and it cost about $900 for about 12m, along with some other work I got done. I did all the earth works also so if I paid for these it would have cost more.

If my plumbing was suitable, the gas feed was suitable and we had other appliances on gas I think they're excellent, if not I'd consider a storage cylinder.

timmmay

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#658737 19-Jul-2012 22:15

mattwnz:
timmmay: Thanks Niel, makes sense :) Heat pump hot water isn't economical yet unless you use use a heap of hot water, according to consumer.

They are often used for underfloor heating, heating the water for the pipes.

That's the way I'd try to do it too, but as a hot water cylinder heater, given the cost, they're not economical yet as far as I've read. Once prices come down they may be.

I wouldn't have space for one anyway, unless it's in the ceiling and air ducted in, or the outdoor unit separate from the cylinder. There's no space around my house that wouldn't be an eyesore.

I'd quite like one monster heat exchanger unit running hot water, under floor heating, and central heating, but I don't think it's viable yet.

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Snowflake

#658762 19-Jul-2012 23:19

i've had regular cylinder, gas mains cylinder and instant system. when i renovated an old house i went with the instant again.

one thing i like is being able to set the temp to 37degC, set the number of litres to deliver, turn on the bath and walk away. perfect temp for the kids, doesnt overflow, and you dont accidentally fill the bath too much.

being able to set the temp also means you can crank the shower nozzle all the way round and just use the hot water delivered & taps running, and toilets flushing, make no difference to the pressure of the shower.

yes, there is a 5-10 sec delay before the water heats up, but the conveniences outweigh the inconveniences in our house :-)

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