Instantaneous Gas Water Heater... umm, Problemmo...

[Batpig]

Hello Everyone,

I’ve been taking a closer look at Instantaneous Gas hot water heaters lately, and they certainly look the goods except for one major flaw - Minimum Flow Rate. Yes, I said Minimum. This is the smallest flow rate required for the electronics inside these things to react and ignite the gas to start the water heating process. At flow rates below this, all you get out of them is unheated water...

The following are the published "Minimum Flow Rates" for a variety of popular models, and I have been told by technical reps from at least two of the companies concerned, that these figures are optimistic if anything:

Rinnai Infinity: 2.4L/min
Rheem Integrity: 2.7L/min
Dux Endurance: 3.0L/min
Bosch Highflow: 2.5L/min
Bosch Hydropower: 3.5L/min
Bosch Pilot: 2.0L/min (except 10P: 5.0L/min)

You can see that the Bosch Pilots (the 13P and the 16P at least) at 2.0L/min, are the best of a bad bunch.

Now tell me this... What happens up here in Sunny Old Queensland if you jump into the shower in the middle of summer and you don’t quite want an absolutely cold shower, but you don’t want a warm one either. You just want it to be lukewarm. I’ve never measured the temperatures involved, but my gut feel is that cold water straight out of the ground in the middle of summer up here is probably about 25deg, and that a comfortable shower with some grease-cutting ability for hair-washing would be at about 30deg in summer - ie. only a 5deg increase above the ambient cold water temperature. Unless you’ve got controllers wired into it, the hot water produced by your Instantaneous Gas unit hanging on the outside wall will be either 55 or 60deg (depending on the brand), unless you purchase one of the models that are factory preset to 50deg. Let’s say you do just that...

Now if your shower rose is flow-restricted to even as much as 9L/min (I say "as much" because some of the new ones are less!), then by my calculations, to have a 9L/min shower at 30deg, you would require 7.2L/min of cold water, and only 1.8L/min of 50deg water out of the hot water system. The result - none of the above units will even turn on! The problem would only worsen for even more efficient shower roses (which the government up here will eventually want us all to get), or for warmer ambient cold water temperatures, or for even more tepid shower temperatures, or for water heaters that weren't preset to 50deg...

Now if you went the way of controllers to get around the problem, you would need at least two of them - one for the shower, and another for the kitchen sink, laundry tub, vanity basin, etc - and you definitely can’t get two temperatures out of the things at the same time if someone wants to use the sink while you’re in the shower. What’s more, wiring the controllers into an existing cavity brick home would be almost impossible to do neatly...

I know there’s plenty of people out there who absolutely swear by them, but unless I’m missing something, I reckon the whole concept is a bit "half-baked"...

Have any of you had this problem with such units during hot weather?

Many Thanks,
Batpig.

[Gra]

I had a problem with my instantaneous HWS, that the hot water would shut off in the middle of the shower. Removed the flow restrictor from the shower head, no problems.. I use a Rinnai Infinity.

[Master Splinter]

I think you're missing the point of the unit - you don't use the shower's cold tap when using one.

Set to 30 degrees and let it supply you with 9 litres a minute of 30 degree water.

Most (I'd say all, but I haven't explicitly looked for the absence of kitchen controllers) have a minimum of a bathroom and a kitchen controller; once the shower control is activated, the kitchen is locked out from increasing the temperature so the showeree doesn't get to resemble a boiled lobster.

There's nothing in the kitchen (barring coffee, and you use a kettle for that!) that can't wait ten minutes for really hot water while someone has a shower. Kinda like how you can't run lots of cold (or hot) water from another tap in the house with storage heating without the person in the shower complaining anyway.

The three after-construction installs that I am familiar with have all looked very neat; the wires for the controller don't need to drop down below the height of the noggins so the installer doesn't even have to play with long drill bits, and whatever modifications have been needed to the plumbing have been made without huge hole in wall dramas.

[Brickie]

Put a solar unit on the roof, costs more initially. but it will pay its self off in the long run.:)

[bricks]

Hello Everyone,

Now if your shower rose is flow-restricted to even as much as 9L/min (I say "as much" because some of the new ones are less!), then by my calculations, to have a 9L/min shower at 30deg, you would require 7.2L/min of cold water, and only 1.8L/min of 50deg water out of the hot water system. The result - none of the above units will even turn on!

Many Thanks,
Batpig.


What the sales man doesn't tell you is that in any case a flow restiricted shower head is not reccomended to be installed on an instant hws, you need to get a instant hws shower head or remove the flow restrictor.

Your exactly right in that the unit won't turn on, or it will stop and start.

[juan]

Now if your shower rose is flow-restricted to even as much as 9L/min (I say "as much" because some of the new ones are less!), then by my calculations, to have a 9L/min shower at 30deg, you would require 7.2L/min of cold water, and only 1.8L/min of 50deg water out of the hot water system. The result - none of the above units will even turn on!I have a Methven Kiri Hi Rise Shower head (7.5L) connected to my Rinnai 26 which has 2 controllers and it functions perfectly.

[Batpig]

I think you're missing the point of the unit - you don't use the shower's cold tap when using one.

Set to 30 degrees and let it supply you with 9 litres a minute of 30 degree water.

Most (I'd say all, but I haven't explicitly looked for the absence of kitchen controllers) have a minimum of a bathroom and a kitchen controller; once the shower control is activated, the kitchen is locked out from increasing the temperature so the showeree doesn't get to resemble a boiled lobster.

The three after-construction installs that I am familiar with have all looked very neat; the wires for the controller don't need to drop down below the height of the noggins so the installer doesn't even have to play with long drill bits, and whatever modifications have been needed to the plumbing have been made without huge hole in wall dramas.

Dear Master, I did realise that running a controller and (mainly) one tap in the shower was one kind of solution, hence my comment:


Now if you went the way of controllers to get around the problem, you would need at least two of them - one for the shower, and another for the kitchen sink, laundry tub, vanity basin, etc

but I still don't think this is a cast-iron solution, because the minimum selectable temperature with any of them when a controller is hooked up is about 37deg. Given that you have different temperature showers at different times of the year - no, heck! make that different times of the day for any given time of the year! - and that the ambient in-ground cold-water pipe temperature changes throughout the year, I reckon that you could still run into trouble even with a controller, due to the 37deg minimum. And when I then think about dialling one temperature after another from different ends of the house several times a day, instead of just using the tap to do both temperature and flow - as is the case with Mains Pressure Storage - I just can't help thinking that the whole Instantaneous concept is still half-baked. Wouldn't be the first time in recent history that substance lagged behind hype. Needs more thought, I reckon...

And don't forget, I'm cavity-brick, so no neat 'n easy retro-installs...


What the sales man doesn't tell you is that in any case a flow restiricted shower head is not reccomended to be installed on an instant hws, you need to get a instant hws shower head or remove the flow restrictor.

Your exactly right in that the unit won't turn on, or it will stop and start.

Thanks for confirming that Bricks. I've never heard of those "Instant HWS Shower Heads". Pray tell who might make some?

Thanks to all so far,
Batpig.

[Master Splinter]

...minimum selectable temperature with any of them when a controller is hooked up is about 37deg...

And don't forget, I'm cavity-brick, so no neat 'n easy retro-installs...

Batpig.

The ENVSMT unit starts at 31 degrees: http://www.rinnai.com.au/hotwater/home/specification.asp?whs=home&pg=5

And for cavity brick, there's wireless: http://www.rinnai.com.au/hotwater/home/wireless.asp?whs=home&pg=4

[wonderplumb]

Pull the restrictor out of the shower head you have, its fairly simple.
They are a pain in the neck, I put in a fancy Grohe shower rose for a lady the other day, cost her around $300 and i asked her if she wanted the restrictor removed because she wouldnt get the full benefit from it.
"Oh no" she said, save water and all the rest.
She called the next day describing the same symptoms while trying to have a 'warm' shower. She could only have a hot one.
Pulled the restrictor out and good as gold.

[Batpig]

Dear Wonderplumb,

Did she have controllers on her system?

Thanks,
Batpig.

[tameriska]

I am not sure about the other brands, but Rinnai at least has I R wireless controllers available for some models

[Smurf]

Messing about adjusting the temperature of the hot water would be a bit irritating in my opinion. I like being able to run the washing machine on warm, fill the sink with genuinely hot water or whatever while the shower is going. Also I like having the temperature control inside the shower rather on a wall somewhere and I do adjust it during the shower most times - I want it a bit cooler when I put my head under than when it's just on the rest of my body.

All works wekk with a storage water heater of any type (electric, gas, solar, heat pump) - instant would be OK but I'd want the hot water at least 50 degrees, preferably 60, and adjust it at the tap.

I've heard of people in Tas having trouble with minimum flow with the instant units so presumably there would be even more troubles in Qld etc during summer.

[wonderplumb]

Dear Wonderplumb,

Did she have controllers on her system?

Thanks,
Batpig.
No mate it was a Rinnai 26 factory set at 50 degrees.

[Batpig]

Messing about adjusting the temperature of the hot water would be a bit irritating in my opinion.

Amen Brother Smurf!


I've heard of people in Tas having trouble with minimum flow with the instant units so presumably there would be even more troubles in Qld etc during summer.

Amazing... Just goes to show that mankind has this nasty never-ending habit of concentrating on the glossy brochure for each new technology that comes along well before he nuts out the essential technical issues (happens with everything nowadays: every new version of Windows, DVD formats, even with the way that Mulching Mowers clag-up so quickly underneath compared to the old-style Catcher Mowers...)


No mate it was a Rinnai 26 factory set at 50 degrees.

Thanks Wonderplumb. Yes, that would be the best bet. 50deg preset will increase the flow rate being asked of the unit for any mixed water temperature at the shower, compared with the otherwise 55 or 60deg output. Combine that with removed Shower Rose restrictors and you might be okay...

Still can see some problems though... You get up in the morning and turn the mixer lever all the way to "hot" until the pipe clears and heats up, then you turn it down a bit and add some cold water. Opening the cold water line will cause a pressure drop in the cold water feed to the Instantaneous, and since there will always be a delay for the existing hot water in the line to come through, you wouldn't therefore know straight away whether or not you'd inadvertantly dropped the flow rate through the Instantaneous to below the required minimum. Would be a case of repetitive, delayed "cause and effect"... Controller would be a pain in the R's for reasons already mentioned, and would only get you down to 37deg for the smaller size of unit that I need anyway, so you're still playing Ducks And Drakes with the delay in finding out whether or not the Instantaneous unit has actually switched off on you... Will be more of a problem up here too, of course, due to the ambient heat in summer...

Thanks guys,
Batpig.

[Smurf]

Just point about the flow restrictors.

The supposed benefit of the instant units is that they use less energy. Unless you don't have somewhere to put a decent sized tank, that's really the only benefit.

But if you're going to increase the flow through the shower in order to make the instant unit work properly then that will undo much or all of the energy savings from having the instant unit in the first place.

Obviously they do work well in many situations but they're not a perfect technology that suits everyone. Likewise electric, solar etc also have their limitations and aren't always the best option.

[Batpig]

The supposed benefit of the instant units is that they use less energy. Unless you don't have somewhere to put a decent sized tank, that's really the only benefit.

But if you're going to increase the flow through the shower in order to make the instant unit work properly then that will undo much or all of the energy savings from having the instant unit in the first place.

Dear Smurf,

You and I can both see that, but do you think those clowns in State Government up here thought about it when they came up with this whole ill-conceived "Post-2010 Phase-Out of Domestic Electric Hot Water Systems" krap?... The whole issue is an utter nightmare, especially for old unit blocks that don’t have gas yet, nor anywhere to put any small individual gas storage units that might get around the massive water wastage that is going to result from the en-masse uptake of instantaneous gas units. And as you have said, more gas will be burnt anyway because the required hot water flow rates will have to be higher for the instantaneous units than with mains-pressure storage heaters...

Utterly crazy, hey...

Best Wishes,
Batpig.

[wonderplumb]

IMHO, the best way to go for HW is a reticulated system off a gas storage HWS. They dont use much more gas than a rinnai, and the circulating pump uses bugger all energy.
Should I ever be fortunate enough to actually build my own place it will be flow & return off a gas storage HWS.
Only draw-back is the cost of initial installation gets up there but man its worth it.

[Batpig]

Dear Wonderplumb,

That one makes a lot of sense, but I'm a bit worried about the heat loss in all of that pipework, because the pipe runs would all have to be external in my situation - possibly as much as even 30m of it - and the hotter something is, the quicker the heat radiates out from it. Even if it was all lagged, it would still be like a big oil-heater, heating up the outside world for everyone to enjoy (unless it was summer...) But it does make a lot of sense, because as Smurf has implied, removing the restrictor in the shower head to get hot water flowrates above the required minimum for an Instantaneous, will just mean that the advertised efficiency gain from the Instantaneous over the Storage will be fretted away, either in part or possibly whole. And you wouldn't have all of that on/off toggling krap going on either...

You know what would be good?... an automatic recirculation pump - ie. where you didn't have that constant heat loss from continuous circulation, but you didn't have to press a button like you have to on a Chilli Pepper or a Water Guardian either. All you would do was turn a hot water tap on, and the sudden flow was sensed electronically, and if the water temperature was less than about 40deg, the water was automatically pumped back to the tank along the return line until 48deg or so had been achieved, whereupon a valve was opened permitting flow to the house or flat, and the pump was turned off - all automatically... I might start another thread on it, because your idea of MP Gas Storage solves so many other issues.

Many Thanks,
Batpig.

[Pheonix]

Looked at one of those "instant heat" units for my hws. (Dux quick recovery gas)
They wanted over $1000 for it:(

[juan]

I think you're missing the point of the unit - you don't use the shower's cold tap when using one.

Set to 30 degrees and let it supply you with 9 litres a minute of 30 degree water.The problem is that you cannot set them all down to 30 degrees as the lowest setting on most of the standard ones is 37 degrees although the Rinnai ENVSMT model can be set down to 31 degrees. In Adelaide we get real hot weather (national champions for it) and with the Rinnai set to minimum it a bit chilly for me. I like about 40 degrees. But have encountered no issues with mixing cold water and ran shower head at about 30 degrees yesterday by mixing cold water and it functioned perfectly. I have my unit outputting at 60 degrees max but the bathroom is tempered to 50 degrees with a tempering valve. I guess the valve is doing nothing unless someone forgets to drop the controller temperature after using 60 at the kitchen sink.
I love our Rinnai 26 Plus instantaneous HWS and can see a significant decrease in gas costs since I changed over from the gas storage unit.

Cheers

[Smurf]

Dear Smurf,

You and I can both see that, but do you think those clowns in State Government up here thought about it when they came up with this whole ill-conceived "Post-2010 Phase-Out of Domestic Electric Hot Water Systems" krap?... The whole issue is an utter nightmare, especially for old unit blocks that don’t have gas yet, nor anywhere to put any small individual gas storage units that might get around the massive water wastage that is going to result from the en-masse uptake of instantaneous gas units. And as you have said, more gas will be burnt anyway because the required hot water flow rates will have to be higher for the instantaneous units than with mains-pressure storage heaters...

Utterly crazy, hey...

Best Wishes,
Batpig.
I wonder if the Qld government realises that water consumption will certainly rise with these units? Every time you turn on the tap, several litres are wasted before hot water comes out of the unit (in addition to having to run it through the pipes). That's not necessarily a reason not to use them but it's clearly a case of less power, more gas and more water being needed.

[Batpig]

I wonder if the Qld government realises that water consumption will certainly rise with these units?

ummm........................NO!

Does that answer your question regarding the IQ of our pollies up here?...

Listen, Smurf, while you're on line, would you mind popping down to this thread for a bit? (unless you're already down there...)

http://www.woodworkforums.ubeaut.com.au/showthread.php?t=68754

Thanks Muchly,
Batpig.

[BrissyBrew]

I wonder if the Qld government realises that water consumption will certainly rise with these units? Every time you turn on the tap, several litres are wasted before hot water comes out of the unit (in addition to having to run it through the pipes). That's not necessarily a reason not to use them but it's clearly a case of less power, more gas and more water being needed.
I have a Bosch 17e instantaneous gas hot water system which I am happy with, $790 from my local pumbing outlet.

I understand the issue however with water wastage and was reading an article in fine home building (US publication) where the issue was not water wastage but water temp going hot-cold-hot between showers, with some elaborate plumbing and a very small electric hot water system/tank located in the bathroom they had a system that did not have the cold water (waste) and recirculated/recycled cold water sitting in the hot water pipe.
The truth, about electric hot water systems, gas we have and is cheap to pump around, spare capacity for electricity generation in queensland we dont have. Power plants are expensive to build and now politically damaging, because the cheapest solution is coal fired power stations = C02 or nuclear which has its own political and waste issues. This is why conserving electricity use, without necessarily conserving engergy appears to be the real motive behind switching off electric hot water systems.
Now I know many people on this forum will advocate for cheaper alternative power sources such as solar, wind, hydro, tidal power, however I fail to remember when the last time was that the mother earth donated any money to any political party. Until people realise that the air they breath and the food and water we consume maintains our life, and not interests rates as the top issue at an election I dont hold much hope for green energy providers. Not to mention that fact that the major oil and gas companies hold the patents for a lot of the green energy technologies, eg efficient solar. Every wondered why BP uses solar on its service stations, because by doing so it means they are "using" the technology in a commerical manner and this protects their patents on the technology.
Sorry about the rant!

[MonkeyWrench]

As a plumber I believe it is a legal requirement that all we install complies to the WELLS rating system. Removing flow restrictors from shower roses could put you into even more hot water (if someone reports ya).
When my mains pressure cylinder blew up I replaced it with a renai 20, big mistake. Now I run the hot basin tap while I shower to keep things cool in summer.

[Batpig]

Thanks MonkeyWrench, that makes three of you Plumbers (incl. Bricks and WonderPlumb) all confirming the issue...

I guess it would be fair to say that the units must have been great before WELS restrictors came in, but there's no way the manufacturer's haven't been getting adverse post-WELS feedback for a while now along the lines of what we've been discussing... So you've got to wonder - why have they been sitting on their hands? :?...

Mains Pressure Storage - looks like you and me are going to be friends for a little while longer at least...

Cheerio,
Batpig.

[bricks]

As a plumber I believe it is a legal requirement that all we install complies to the WELLS rating system. Removing flow restrictors from shower roses could put you into even more hot water (if someone reports ya).
When my mains pressure cylinder blew up I replaced it with a renai 20, big mistake. Now I run the hot basin tap while I shower to keep things cool in summer.

I put this to my local SA water inspectors and if the fine print is read then you can actually remove the flow restrictor in a shower head where instantaneous gas heaters are installed. The reason being that the flow restrictor is to reduce the flow rate to under 10 lt/minute, ( for the wells rating) a gas instantaneous unit won't allow you to have more than that anyway. Plus the flow restictor is actually rendering the operation of the heater inefficient. That is the case apparently for SA, however you can now buy instant unit shower heads, so this may change. When you remove the flow restictor you also void your warranty on the tapware possibly?

[namtrak]

For what its worth, we installed Rinnai 24 in the house we just finished about 6 years ago, and it has never missed a bit. We had flow restrictors in the shower and kitchen, and controllers in both. Bath controller runs from 37 to 50 and kitchen controller runs from 37 to 55. We all only use hot water, but have had no problem on hot days when mixing the hot and cold.

We also just installed a second bathroom controller with flow restrictor in the new ensuite and it also hasn't missed a beat. 4 people regularly showering, cleaning etc.

We will eventually retro-fit a solar system and use the gas system as a back-up.

Our energy costs have halved.

Our mains water flow into the house is around 30/35 lpm.

The house we have just moved into in Queanbeyan has a Rinnai 26 and also has flow restrictors, and as yet no problems. Although there are no controllers installed - something we will rectify as we renovate.

[Smurf]

If you use a heat pump then electricity is at least as efficient from fuel in ground to hot water at the tap. In most cases it is more efficient though not by much. Ordinary electric systems are a lot less efficient than either heat pump or gas however.

In terms of power generation capacity, if you run it on off-peak then you are NOT adding to peak power demand and thus not adding to the need for new power stations. All you are adding to is the need for fuel to run them - but that's comparable to gas if you go the heat pump option.

The exception is Tasmania where hydro-electric power generation by its nature is energy constrained rather than capacity constrained. That is, the limit is not the capacity of the turbines but the water to run them. So new schemes were built when total, as opposed to peak, usage increased. All of the Tas hydro schemes were built with capacity to use the water - they didn't add turbine capacity specifically to meet peak loads although in practice they ended up with enough anyway due to the nature of the water storages and thus the turbine capacity they needed.

All the mainland states have spare capacity in the middle of the night to run off-peak loads. Tas has plenty of turbines sitting idle at night but you'd still be adding to the water use which the limit on system capacity (and the system is fully utilised even with normal rainfall - Tas is a net importer of electricity from the other states). That said, Tas can access additional energy, as opposed to capacity, from the other states and from gas-fired generation without too much difficulty.

So from an efficiency perspective heat pumps or gas wins over electric. Solar with electric boost is a winner only if it will heat more than two thirds of your water - good in some places, not so good in others. Solar with gas boost would be more efficient than any of the others if the system works properly (I've heard some horror stories with these units however).

Financially, gas and off-peak are similar running cost for the energy. How you use it will determine what the actual bills are. Heat pumps and solar are cheaper to run as long as they're on an off-peak tariff.

[Batpig]

Dear Smurf,

Nice contribution... :wink:

Regarding this:

Solar with gas boost would be more efficient than any of the others if the system works properly (I've heard some horror stories with these units however).

Any chance of an elaboration on the nature of the problems being encountered with this solution?

Thanks,
Batpig.