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xlinknz:
Hi all
Our gas usage has gone up >50% by volume over the last 6 months. For the last month were were extra dilligent on hot water use e.g. showers etc with little change.
Downers confirmed no gas leaks (and meter ok) which only leaves the 20 year old Rinai Infinity 24 to be checked for efficiency etc
Has anyone either found their Gas Instant Hot water heater significantly inefficient or replaced an old unit?
Also if it requires replacing I am tempted to replace it with electricity instant heated hot water if available (but leave gas for oven top)
Can't comment to much on your current gas use.
For gas instant hot water heaters, standard units are generally around 80% efficient. But high efficiency models like the Rinnai NB series exist that are around 97% efficient. More focused at commercial applications that are going to see a heap more run time than a residential application, but an option that exists. This particular one may be a bit big / expensive for a single home residential application, but I assume other brands make smaller ones:
https://rinnai.co.nz/water-heating/gas-hot-water-systems/residential-and-commercial-use/rinnai-infinity-nb-series-internal-and-external
On instant electric, I have specified one of these before: https://www.stiebel-eltron.co.nz/del-plus-three-phase-instant-water-heater
Was for a sizeable pump station, so several hundred kW of electrical capacity. And the facility is not regally staffed, so it would spend most of it's life off... Felt it was good selection.
The larger size is roughly equivalent to a Rinnai A16 (~ 16L / min at 25 degree rise), so is a step down in capacity to your current Infinity 24 (assuming it is working properly, which is under question).
For context a common shower head provides around 14 L / min, and a WELLS 3 star shower head can still provide a good shower with 9L/min.
So you can run a single shower fine, but where your 42 kW gas unit could handle two showers at the same time (12 L / min each), the 28 kW instant electric would be close to being able to supply two 3 star showers (not quite as hot as normal, but still OK), but two common shower heads would result in disappointing performance.
So it comes down to how much hot water stuff you want to run concurrently...
Also note you need a heap of power. Smaller of the two units need 27A 3 phase (32A breaker), and the larger size needs 38.9A 3 phase (40A breaker).
In Auckland Vector offers 1 & 3 phase connections, with 32A, 60A or 100A pole fuses. Would likely want the latter if you are want to go this route.
In general most NZ houses with electric hot water run a storage cylinder. Means the water can be heated over a longer period of time with 13 - 16A of single phase power... Meaning it is fine for a house like mine to have a cheaper 60A single phase connection. Standing losses on modern cylinders are small (around 1 kWh / day for a 180L if I recall correctly), Both big (300L & 400L) cylinders, and rapid recovery (below one is 26A single phase) cylinders are available:
https://rheem.co.nz/products/home/electric-water-heating/mains-pressure-vitreous-enamel/31230033
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As a general note, NZ's natural gas reserves are declining way faster than expected, and (while they love to talk up biogas & Hydrogen lends), the gas piping network is in a bit of a death spiral as they try to eek every bit of money they can out of a declining customer base (meaning their opex costs are shared less ways). Generally I suggest people move off gas as appliances come up to end of life.
Note if you are on natural gas, your daily charges will be brutal if you are only using it for the cooktop. (savings from gas being cheaper than power generally, which if you use a bunch means your savings can cover your daily connection charge).
Might need to consider swapping the cooktop for induction at the same time (may require a new wire run, which can be hard), or having it converted to run off LPG 9kg Bottles.
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