How much is your gas bill?

yeah not sure whats on the roof for insulation.. an inspector commented that i have thick layer of insulation during an asbestos inspection..

 

You mentioned you have a Rinnai instant hot water system so if I take a punt that it is the Infinity 26, which uses 199MH/Hr, and there are approx 37MJ to the cubic metre, that equates to running the hot water on full with no cold water for about 11 minutes, which sounds a bit excessive for a shower. More realistically, you might have one of those water saving shower roses installed, which limit water flow rate to 9 litres per minute, which would give you a shower time of around just over 30 minutes and even longer if you mix some cold water in too.

For comparison, my 3 star 310 litre storage hot water system uses around 1.2 cubic metres of gas a day in summer and 1.5 in winter. This provides 3 showers a day with 9 l/min water saving shower roses of 20 minutes total of which 20% of cold water is mixed in (ie. 0.8 x 9 x 20 = 144 litres of hot water daily) , a load of washing on warm every other day (say 20 litres of hot when used, so 10 litres per day), and hot water for washing dishes in the sink twice a day (say 10 litres total). This totals 164 litres of hot water a day, which a Rinnai Infinity 26 would need to run on full for 6.3 minutes to produce for a total consumption of (6.3 x 199 / 60) 20MJ or 0.56 cubic metres for the entire day. In my case at least, a Rinnai Infinity 26 should nearly halve my hot water heating cost!

In consideration of the above, the only ways that you can be getting as high a reading as you did for your one shower are that either:
1. You are having very long showers with high pressure hot water,
2. Your ducted gas heating came on while you were having a shower, thus corrupting your reading,
3. You have a major gas leak, or
4. Your gas meter is reading incorrectly.

If #1, install water saving shower roses and cut down shower times.

If #2, do the test again with the ducted gas off.

To check #3, read the gas meter, turn off your ducted gas and don't use hot water for 30 minutes, then read the gas meter again. The change should be zero.

To check #4, read the gas meter, make sure no one uses hot water for this test, turn on your ducted gas and raise the temp a couple of degrees above the current room temp, turn it off after exactly 5 minutes of running (from when you turned the temp up, not when the fan came on, which is delayed), read the gas meter again, find out what your ducted gas heater's gas flow rate is from the following spec list Product range and specifications then calculate what your consumption should have been compared to what you actually used (after converting to like units). If you have trouble with the calculations, post up your readings and specific gas unit model number and I'll work it out for you.

 

Yes I have a Rinnai 26 Infinity. I have a 3 star Estillo shower head that runs 9L per minute....just tested again by turning off the ducted heating and no changes in cubic m for 10 mins shower.. the other two times I have done it, the ducted heating was off but on program mode.. average about 6 showers per day in the household.. not sure why it was 1 cubic m last time.. perhaps slightly longer shower..

4. A bit too technical for me to convert.. but here is the test number no change in the black and white digits for the gas meter.. the red one went from 574 to 765.... unit is TQ 420 Ecoair..

 

Strange with your shower use reading nothing at all. You should read the red digits like you did with the ducted heater test as a shower is only likely to use decimal places of a unit's use.

With your ducted heating test, you consumed 0.191 cubic metres over 5 minutes, which is 7.1MJ. Your furnace is rated at 80MJ/hour, which is 1.33MJ/min, so 5 minutes use should consume 6.7MJ. Your reading is 6% higher which IMO is within testing tolerance, so I think your meter is OK.

Apart from trying the 30 minute leak test I suggested previously, another thing you can do is note how often your heater is coming on in an hour to maintain 17C. At 80MJ/hour, it roughly takes 3 minutes to use 0.1 cubic metres so 30 minutes cumulative use is 1 cubic metre. For comparison, over the last week mine comes on for 10-15 minutes in the late afternoon to get up to 19C from say 17/18C, but then is only on for 3 minutes every 30-45 minutes to maintain that temperature. Ours is a 26KW unit and chews through approx 127MJ/hour, so we use 0.1 cubic metres every 2 minutes, 50% more consumption than yours but with 44% more heat output which balances it out.

 

kindda like this experiment.. sorry didn't read the meter correctly for the water heater... i used a stopwatch now for accuracy... 14 mins shower consuming 0.519 cubic metres... prob consume about 3 cubic metres in the household a day..

i have set the heater from 9pm to 1am at 18C.. and 7.10am to 8am at 18C..
house is at 12C.. the heater was continuously on for 2 hours to heat up to 18C...

total cubic metre used 10 per day with this setting..
comes down to insulation i think.. the house is not well insulated and have difficult time restoring the heat.. bought some thermal curtains online.. will get it soon and hope that will help..

thanks for your clear explanation.. i find it very helpful..

 

That's a much more realistic consumption for that time period.

That's about 4 times longer than it should take in a well insulated and sealed house. This seems beyond just an insulation issue. I suspect your ducted gas furnace is drawing in a swag of outside air from somewhere rather than recirculating internal air like it should, thus handicapping your heater's performance.

You can borrow an energy assessment kit from your local library that has a non-contact thermometer like this: http://www.jaycar.com.au/non-contact-thermometer-with-dual-laser-targeting/p/QM7221 to help find a possible draft source and the coverage of your insulation. When I initially checked out my house, I found the main bathroom IXL tastic was allowing outside air directly in to the ducted gas furnace intake with the thermometer showing a very low temperature line straight to the tastic. I reckon about 50% of the gas consumption drop I experienced came from fixing this one thing. The thermometer also showed the big gaps I had in insulation around down lights and ducted evap cooling vents (as much as 0.5 metre sections missing from when the tradie installed it for the previous owner), which prompted me to fill the gaps then beef up the insulation overall and give me the rest of the gas consumption drop.

BTW, it's not just about lower gas bills. Sealing off drafts and improving insulation makes for much more comfortable living areas, even at lower temperatures. When my wife is at work some mornings when it is cold, I don't even bother turning the heater on at all and can quite happily sit in a 15C room with the morning sun streaming in and be completely comfortable.

 

the heating unit is installed below the house.. yeah i will check it through.. good idea.. will see how long for it to get to 18C tonight.. its been 40 mins and still running...

 

I have added total blackout curtains this year and can't believe the difference it makes in keeping the house warm. Previously I had the mid blackout lining on the curtains. There is an enormous difference in the installation of the heaviest lining

 

I covered our main bedroom window (old house, crappy thin window) with bubble wrap.. Seems to help but hard to measure

 

I've been running the electric heaters and gas heaters non stop and dryer.... this bill is going be shocking!

Not much you can do when kids are sick though. Just gotta grin and bear.

 

It was newly installed last Monday, a bit shy of two weeks..Presuming its new and shouldn't have problem.. I have called the installer... they find it odd too and asked me what level was the fan set to.. it was set at 7.. what fan setting do you use? they will send someone in to check...