Instant vs Gas cylinder hot water

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#658801 20-Jul-2012 00:20

I retrofitted an instant gas system to my old (very old) house after having had one for years in other places. Time lag between turning on the tap and receiving hot water depends almost entirely on where the unit is situated. In my place, I was able to put it on the outside wall of the main bathroom so the bathroom takes only seconds to get the hot water. The kitchen is further away and takes a little longer.

In my previous house I had the controllers and loved them. In this place I opted to go without the controllers to save money. You should look at these if your household includes kids though.

Price-wise, moving from the electric hot water system in this house to the instant gas has resulted in a huge saving.

One caveat - water pressure can affect the effectiveness of hot water delivery. In my previous houses I had no problems with hot water being used in multiple locations at the same time. Two people showering in different bathrooms would have a good, regular, stable temperature supply of water. In this house, with really low water pressure, its not possible to run two different showers or even run any other hot water while someone is in the shower. So, check your water pressure before deciding.

corksta

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#658811 20-Jul-2012 02:32

We just changed to a gas instant flow system two weeks ago from a standard hot water cylinder, so haven't had our first bill yet.

Subtle things we've noticed is that pressure seems to be slightly stronger, but it does take a little longer to heat up, however we can deal with that knowing the hot water is never going to run out. We aren't spending longer in the shower, so we're looking forward to seeing a lower power bill!

It cost us about $3,000 to set up which included connecting to the mains supply, the unit and installation of it, and the electrician to wire it up.

davidcole

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#658819 20-Jul-2012 06:24

I'm with regs. Leaving the hot water tap on hot and knowing it will be perfect temp (and why waste the heat by cooling it slightly?)

I'd recommend one controller in the kitchen (that has the kitchen override for 55 degrees. And one near your main shower (or each shower) then you can dial the temp as needed.

When the unit is in use others can use the water, but no one can adjust the temp.

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kiwitrc

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#658820 20-Jul-2012 06:33

davidcole: I'm with regs. Leaving the hot water tap on hot and knowing it will be perfect temp (and why waste the heat by cooling it slightly?)

I'd recommend one controller in the kitchen (that has the kitchen override for 55 degrees. And one near your main shower (or each shower) then you can dial the temp as needed.

When the unit is in use others can use the water, but no one can adjust the temp.

Whats the story re legionella and not having the hot water go up to 60 as is required in cylinders, anyone know? Its always seemed stupid to me to stipulate cylinders have to heat to 60 to kill legionella and then stipulate the hot water from the cylinder cant be more than 55??

Wondering how inline systems get building approval?

davidcole

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#658821 20-Jul-2012 06:36

Not sure actually. Maybe cos it's not being stored warm?

You'd have to ask whoever sets that rule how instant hot water systems aren't covered by the same rule.

corksta

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#658837 20-Jul-2012 07:43

Actually I forgot to add you'd be amazed at how much silt, dirt, and crap builds up in the bottom of the hot water cylinder. Ours was only about 8 years old, but when it was drained there was about two litres of gunk on the bottom, which is just natural buildup from the water in the cylinder. Seeing that stuff ooze out and suddenly you didn't feel so clean.

Skolink

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#658881 20-Jul-2012 08:58

kiwitrc:
Whats the story re legionella and not having the hot water go up to 60 as is required in cylinders, anyone know? Its always seemed stupid to me to stipulate cylinders have to heat to 60 to kill legionella and then stipulate the hot water from the cylinder cant be more than 55??

Wondering how inline systems get building approval?

The building code stipulates that for solar systems (with electric backup), the cylinder only has to reach 60°C once per week. Our controller isn't that smart, and doesn't control the electric element, so in winter I have the element thermostat set to 60°C. It does result in a bit of unnecessary heating. In summer I set it to 50°C just for those few days where the cyclinder doesn't reach 90°C.

There is no storage in a inline system, so nowhere for the legionella to grow. You'd think there might be a risk of it growing in the pipes after the heater, esp with lagged pipes keeping it warm for a long time. Obviously it must just get flushed out.

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#658989 20-Jul-2012 11:39

kiwitrc: Its always seemed stupid to me to stipulate cylinders have to heat to 60 to kill legionella and then stipulate the hot water from the cylinder cant be more than 55??

Don't you have a tempering valve after the cylinder, so the cylinder can be hotter, but the out-flowing water is always mixed down to the target 55degC or so afterwards?

I'm not sure, as in would have to check, but it's probably more of a concern on non chlorinated (rain/river/dam etc) supplies than town supplies. Presumably, with no storage capacity the on demand systems are not as prone to having a large supply of water standing unused for a long period of time.

kiwitrc

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#658992 20-Jul-2012 11:45

Jaxson:
kiwitrc: Its always seemed stupid to me to stipulate cylinders have to heat to 60 to kill legionella and then stipulate the hot water from the cylinder cant be more than 55??

Don't you have a tempering valve after the cylinder, so the cylinder can be hotter, but the out-flowing water is always mixed down to the target 55degC or so afterwards?

I'm not sure, as in would have to check, but it's probably more of a concern on non chlorinated (rain/river/dam etc) supplies than town supplies. Presumably, with no storage capacity the on demand systems are not as prone to having a large supply of water standing unused for a long period of time.

Yes correct that is how it works, but the tempering valve mixes cold water with the hot down to 55 max so I dont understand why then legionella cant grow in the pipes? It just seems to defeat the whole purpose of raising the temp to 60 in the first place.

mattwnz

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#659021 20-Jul-2012 12:43

A few things to note are that the life span of these things isn't that long. A plumber who serviced them in a retirement village said you are lucky to get 10 years out of them, vs a hot water cylinder which can last 20 years +, some can last 40 years.
Also if something goes wrong electronically, they can be difficult and expensive to repair, and often you just swap out for a new one.

timmmay

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#659041 20-Jul-2012 13:05

High pressure hot water cylinders last 10-15 years according to my plumber. Low pressure ones can last much longer.

Jaxson

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#659044 20-Jul-2012 13:09

Yeah, you have no storage of warm water any more, so no hot water in a power cut etc if that's an issue.

I've not notice any significant hot water delays, other than a 5 second max type pre heat time. Supply delays will be the same as before, unless your cylinder is closer to your point of use than the new location of the instantaneous unit. They come on pretty quickly once they detect flow, but can be quite noisy, so I'd think carefully about what's next to the unit. Probably not ideal if it's a bedroom etc.

I assume the water in supply pipes is likely to hang around less than in a cylinder so it's less of a legionnaires risk. ie the bugs have more residence time in a cylinder, as they might be able to hang out there for a long time before being flushed out, especially if the tank is not being completely emptied each time it's used.

kiwitrc

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#659047 20-Jul-2012 13:11

Jaxson:

I assume the water in supply pipes is likely to hang around less than in a cylinder so it's less of a legionnaires risk. ie the bugs have more residence time in a cylinder, as they might be able to hang out there for a long time before being flushed out, especially if the tank is not being completely emptied each time it's used.

Yeah that may well be the case.

Elpie

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#659081 20-Jul-2012 14:04

Jaxson: Yeah, you have no storage of warm water any more, so no hot water in a power cut etc if that's an issue.

Depends on the system. Some only use electricity to spark ignition and can be safely fired with one of those gas clicker thingees. I'd check with the installer to make sure this is safe with whatever system you have though! I used to safely do this with my old system but don't know how safe it is with the Infinity.

Jaxson: They come on pretty quickly once they detect flow, but can be quite noisy, so I'd think carefully about what's next to the unit. Probably not ideal if it's a bedroom etc.

If an Infinity system is noisy I'd get it checked out. Mine makes no noise at all but I guess a lot of different factors come into play with these systems.

Jaxson: I assume the water in supply pipes is likely to hang around less than in a cylinder so it's less of a legionnaires risk. ie the bugs have more residence time in a cylinder, as they might be able to hang out there for a long time before being flushed out, especially if the tank is not being completely emptied each time it's used.

Makes sense. The water is completely flushed out every time a hot water tap is turned on. Even with insulating the pipes the initial flush is almost always too cold for legionnaires.

mattwnz

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#659082 20-Jul-2012 14:07

timmmay: High pressure hot water cylinders last 10-15 years according to my plumber. Low pressure ones can last much longer.

Our last gas mains one lasted 40 years. The current one in the house is already 20 years old.

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