High gas usage

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Paul1977

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#222960 5-Sep-2017 15:56

We had a gas continuous hot water system (with 2x 45KG LPG bottles) installed in October last year. We also had gas pre-piped under our kitchen in preparation for a kitchen renovation which has subsequently been put on hold, so as it stands at the moment the only thing we use gas for is hot water. There are only two of use in the house and we do mainly cold clothes washes.

We don't have temperature controls in kitchen or bathroom, it is set at the unit to 55 degrees and we just mix in cold to get the desired temperature.

We aren't using hot water any differently, but have had significant variation in how long a gas bottle lasts, with the last two being especially quick to deplete.

Bottle Replaced Days Lasted

5/10/2016 46

20/11/2016 49

8/01/2017 75

24/03/2017 53

16/05/2017 41

26/06/2017 35

31/07/2017 35

I haven't properly weighed a bottle after the valve switch over to see if it is really empty, but I have physically lifted it and it feels pretty empty to me.

Could this large variation be attributed to it requiring more gas to heat the water in Winter, since presumably the cold water coming in is colder than in Summer?

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1049 posts

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#1859092 5-Sep-2017 16:05

Seems about right.

I'm in a place (as a renter) at the moment with 2 x 45kg Gas cylinders too, and only used for hot water and cooking. Our household is 2 adults and 2 kids under 10. Adults are showering twice a day, and we call for a cylinder every 4 weeks or so at the moment, less often in the summer months.

wellygary

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#1859093 5-Sep-2017 16:08

Yip.

Colder water needs more heat , + you subconsciously spend longer in the shower in colder weather...

Aredwood

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#1859129 5-Sep-2017 17:15

Do you always leave both bottles turned out all the time? Or do you leave 1 bottle turned off, and only turn it on when the first one runs out?

Paul1977

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#1859178 5-Sep-2017 18:43

Aredwood: Do you always leave both bottles turned out all the time? Or do you leave 1 bottle turned off, and only turn it on when the first one runs out?

Leave them both on so we don't get an unwelcome surprise in the middle of a shower. I was thinking of doing this as a test however to see how long a single bottle truly lasts.

nickb800

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#1859183 5-Sep-2017 18:56

Could it be due to lower temperatures reducing vaporisation of your LPG

e.g. http://www.stuff.co.nz/national/2672638/Rubbish-gas-leaves-users-cold

paulchinnz

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#1859230 5-Sep-2017 20:46

@paul1977 if you leave both on, does that mean you get an unwelcome surprise half as often but have to wait a day or two for delivery of bottle? Or do you run one bottle until about half empty, then turn both on and replace when bottle feels empty?

Aredwood

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#1859247 5-Sep-2017 21:04

The changeover regulator should show a (usually) orange flag to say that the primary bottle (the one the lever points to) is now empty, and gas is being supplied from the reserve bottle. Keep going for a week or so with the reserve bottle supplying your gas before ordering another bottle. This gives time for you to use up any remaining butane in the first bottle that you haven't been able to use yet due to cold temps making it harder to draw from the bottle.

Incoming water temp makes a big difference to amount of gas used. Another factor is colder air temps in your bathroom during winter, means you will turn your shower mixer further round to "hot" during winter. So even more hot water used.

I have seen a study that said that household electric hot water cylinders typically use 60% more electricity during winter than summer. Due to more hot water being used and colder water temps to be heated. I can't see any reason why gas hot water would be any different.

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paulchinnz

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#1859251 5-Sep-2017 21:17

I must have an ancient setup ... my only indications that the bottle is empty are 1) no hot water (or intermittent), 2) bottle feels light and 3) pouring hot water down the side shows low gas level.

Aredwood

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#1859256 5-Sep-2017 21:30

The red parts of the top dial change to green when the main bottle still has gas in it.

the orange indicator disappears when the main bottle has gas.

Both of these regulators are common in NZ, but there are lots of other models as well. Post a picture of your regulator.

Batman

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#1859272 5-Sep-2017 21:47

nickb800:

Could it be due to lower temperatures reducing vaporisation of your LPG

e.g. http://www.stuff.co.nz/national/2672638/Rubbish-gas-leaves-users-cold

Hmm interesting! How to tell if I'm getting the good stuff or the bad stuff?

Oblivian

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#1859278 5-Sep-2017 21:58

Batman:

nickb800:

Could it be due to lower temperatures reducing vaporisation of your LPG

e.g. http://www.stuff.co.nz/national/2672638/Rubbish-gas-leaves-users-cold

Hmm interesting! How to tell if I'm getting the good stuff or the bad stuff?

You can't. It's what turns up in the boat/market sway at the time.

Mixture of Propane/Butane.

mdf

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#1859279 5-Sep-2017 22:00

Do gas hot water heaters have an optimal temperature rise?

5th form physics taught me (IIRC) that if it takes X joules to heat a volume of water to a certain temperature, the same X joules energy would also heat half an amount a water to twice the temperature, or twice the amount of water to half the temperature. But that assumes perfect systems and I am wondering whether heating more (or less) than that decreases efficiency?

I've managed to figure out that the L/min rating is based on a rise of 25 deg above ambient. Is this the setting they are optimised for?

I haven't measured it in terms of gas usage, but it seems to me that we get better water pressure in the shower if we turn down the temperature on the water heater and mix less cold in at the shower mixer. The pressure is worse if the burner temp is higher and we use the shower mixer for more cold.

That might be due to my absolutely craptastic plumbing though, and nothing to do with water heater efficiency whatsoever.

Paul1977

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#1859287 5-Sep-2017 22:16

paulchinnz:
@paul1977 if you leave both on, does that mean you get an unwelcome surprise half as often but have to wait a day or two for delivery of bottle? Or do you run one bottle until about half empty, then turn both on and replace when bottle feels empty?

It's as @Aredwood said on ours - indicator turns red when it switches to the reserve bottle to let you know to order a replacement. I also tend to leave it for about a week after I notice the red before ordering a replacement (as suggested above), as when it gets close to empty it seems to flick back and forth between which bottle it uses for a few days.

Oblivian

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#1859291 5-Sep-2017 22:28

They get less efficient the lower the level too.

And unless you are with a junk provider, the bottles are serialised weighed. They should credit the fill difference

Just don't let them be stolen :) heaps went missing after quakes and it's customer liability.

paulchinnz

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#1859301 5-Sep-2017 22:55

Last time I left both my bottles on (by accident), they ran out more or less simultaneously on a Saturday and we spent 2 days with cold water out of tap. Too cold to wander out to double check right now, but I've never seen red/green indicator with my setup.

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