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Replace continuous flow gas heater with ?







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User #10230 • 8053 posts

AndyB

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posted Tuesday at 4:50 pm



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O.P.

I’m looking for an economical and environmentally-friendly replacement for our continuous flow gas hot water system. Perhaps the most awkward limitation is space: we don’t have much space to work with in the current location: the path between house wall and retaining wall is about 800mm wide and we need access, so a 600mm diameter tank just won’t work.

Options considered:

Heat pump, put it elsewhere. This would likely require re-plumbing because our farthest bathroom is already too far away (~1min to get hot water with current system) so probably not economical. Wife is also not keen on the alternative locations.

Split system heat pump, custom slim tank(s). Not sure if this is possible: can you get < 400mm diameter or depth with custom tanks? If so, are they expensive? Heat pump can go on the roof above.

Electric continuous flow: Single-phase doesn’t provide enough heating for the house. We don’t have 3-phase, nor is our solar/battery inverter capable of 3-phase, so upgrading would be expensive. Probably don’t have enough battery capacity to make it economical either.

Tank on roof: this might be an option if the structural integrity is there. Has anyone done this?

Move the retaining wall: likely to be expensive but the wall is only 600mm high and there is space to move it 500-600mm.

Thoughts and suggestions?









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posted Tuesday at 5:15 pm



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AndyB writes...

Thoughts and suggestions?

How much hot water do you use each day?









User #82466928416 posts

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posted Tuesday at 5:23 pm



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AndyB writes...

Split system heat pump, custom slim tank(s). Not sure if this is possible: can you get < 400mm diameter or depth with custom tanks?

Unlikely given the design of tanks with the heat transfer coil going around the storage tank. Slimmest regular heat pump unit would be an iStore 180 litre with diameter of 540 mm.

Another option might be solar thermal system with roof mounted tank and electric booster. But you'd need suitable roof real estate for it.









User #56984314733 posts

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posted Tuesday at 6:49 pm



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AndyB writes...

put it elsewhere. This would likely require re-plumbing because our farthest bathroom is already too far away (~1min to get hot water with current system) so probably not economical.

25 metres of ½ inch has a volume of about 2 litres. Wasting 2 litres of cold water, plus perhaps another 2 litres of luke warm water before the hot water flows, doesnt turn this potential solution into an uneconomical one.









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mobnet writes...

Wasting 2 litres of cold water, plus perhaps another 2 litres of luke warm water before the hot water flows, doesnt turn this potential solution into an uneconomical one.

Insulating the pipes helps with longer runs, doesn't keep it hot for long but enough for getting ready in the morning, etc.

On the expensive side but you can get < 10 litre electric HWS for inline installation in the bathroom. This would provide hot water straightaway while hot water from the main HWS travels through the pipes.









User #4128323868 posts

JohnVIC3132
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posted Tuesday at 7:37 pm



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AndyB writes...

Thoughts and suggestions?

Under option 5 you are going to have to walk around a HW storage cylinder attached to the home.

I presume you want to go all electric ?









User #10230 • 8053 posts

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posted Tuesday at 7:38 pm



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O.P.

wattmatters writes...

How much hot water do you use each day?

Honestly don’t know, but it’s a 3-adult household with 2 of us having long-ish showers plus guests at times. Based on the manufacturer guidance I expect a 250L or higher tank would be required.

mobnet writes...

25 metres of ½ inch has a volume of about 2 litres

The existing pipe run would be about that. The usable alternative locations would add 15-20m (there is nowhere close with usable space). But probably worth getting some advice on this option: there is additional delay from the gas ignition in the current system, so it might not be a big a difference.

wattmatters writes...

Unlikely given the design of tanks with the heat transfer coil going around the storage tank

What about dual skinny tanks with the coil around both? I assume that the inner tank is the part that needs to withstand the pressure, so has to be circular.

Another option might be solar thermal system with roof mounted tank and electric booster.

Hadn’t thought of that option, thanks. Most of the sunny space near the current system is occupied with solar panels but it might fit. Do solar thermal systems work OK in the southern half of Oz?









User #4128323868 posts

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posted Tuesday at 7:48 pm



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AndyB writes...

there is additional delay from the gas ignition
& initial heating of water ?

Low flow showerheads (say aerated 5LPM = 9.5LPM) increasing warm water wait time.









User #79363611232 posts

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posted Wednesday at 7:33 am



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AndyB writes...

Honestly don’t know, but it’s a 3-adult household with 2 of us having long-ish showers plus guests at times. Based on the manufacturer guidance I expect a 250L or higher tank would be required.

That's a reasonable estimate and you can just let it heat water 24 hours a day when needed if you occasionally need a bit more hot water. If you get a heat pump they don't use much energy.

Based the distance I would consider two hot water systems instead of one









User #143622 • 5733 posts

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posted Wednesday at 8:30 am



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AndyB writes...

Split system heat pump, custom slim tank(s). Not sure if this is possible: can you get < 400mm diameter or depth with custom tanks? If so, are they expensive? Heat pump can go on the roof above.

The CO2 split systems such as Reclaim, Sanden, Thermann use conventional solar-rated tanks (no heat exchanger coils on/in the tank) but even so, the smallest I've seen is 160 litres with 528mm diameter. They do allow a large separation between the compressor unit and tank (10m?) but that probably doesn't help your situation. Reclaim seem to have the widest range of tanks; perhaps you could contact them and see if they have any custom solutions.

Even conventional electric element tanks seem to be 500mm or up for any decent capacity. Perhaps you could consider using a small conventional tank (perhaps Rheem 50 litre, 400mm diameter) as a booster heater located close to your bathroom (maybe even indoors somewhere?), with the main heat pump water heater located where space permits. Not the cheapest or most efficient solution though.









User #7837943186 posts

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posted Wednesday at 9:29 am



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AndyB writes...

The existing pipe run would be about that. The usable alternative locations would add 15-20m (there is nowhere close with usable space). But probably worth getting some advice on this option: there is additional delay from the gas ignition in the current system, so it might not be a big a difference.

This will be a factor. I changed from an old continuous flow Rinnai unit to an Aquatech X8 heat pump in the same location and the hot water arrived at the taps faster. There was a delay with the gas unit from turning on the tap, for it to ignite the gas and start heating. This is one reason I really dislike continuous flow hot water. I also hate how you can't do short bursts of hot water with them, because the water is never running long enough to ignite the gas, and you end up just having cold water.

Do you have a floor plan showing the current location and location of the taps? I'm wondering if a split unit could work with the tank in the garage, or an internal cupboard?









User #56984314733 posts

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posted Wednesday at 9:45 am
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mobnet writes...

25 metres of ½ inch has a volume of about 2 litres.

AndyB writes...

The existing pipe run would be about that. The usable alternative locations would add 15-20m (there is nowhere close with usable space). But probably worth getting some advice on this option:

I doubt you house is 40 meters long.

You dont need run a hot water pipe between any alternative location and the current HWS location.
The hot water pipe can connect to any part of the existing hot water pipes within your house.

In the roof space or on the roof may be potential locations too.









User #408431570 posts

jack-the-lad
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posted Wednesday at 9:59 am



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TheRoyal writes...

Based the distance I would consider two hot water systems instead of one

My previous home had this. Two small Infinity units. Each placed directly adjacent to the bathrooms. Absolutely brilliant.









User #10230 • 8053 posts

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posted Wednesday at 3:37 pm
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posted Wednesday at 3:37 pm (edited Wednesday at 3:50 pm)





O.P.

this post was edited

mobnet writes...

I doubt you house is 40 meters long

House is ~18m wide and ~15m deep. Ensuite is upstairs and almost on the opposite corner to the hot water. Even if it’s a direct line (unlikely) it will be at least 20m, hence my 25m estimate. The only currently-viable alternative location for a hot water unit is ~15m in the opposite direction to the current piping if I go around the outside walls.

The hot water pipe can connect to any part of the existing hot water pipes within your house.

Thanks, good to know that. Not guaranteed that I can put the unit near existing piping, unfortunately. The wider space near the current piping has sewerage access requirements for the council.

EDIT: added note about viable alternative location.









User #10230 • 8053 posts

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O.P.

hound58 writes...

They do allow a large separation between the compressor unit and tank (10m?) but that probably doesn't help your situation

It helps to reduce clutter and give me more height to work with if we put the compressor unit on the roof, but no, it doesn’t solve the depth/diameter constraint in the current location.









User #792374206 posts

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AndyB writes...

Do solar thermal systems work OK in the southern half of Oz?

Had one on our house in the Adelaide Hills. More than enough hot water in summer, off-peak boost as required for the rest of the year.









User #10230 • 8053 posts

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posted Wednesday at 5:51 pm



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O.P.

jack-the-lad writes...

Two small Infinity units. Each placed directly adjacent to the bathrooms. Absolutely brilliant.

The infinity units are gas, correct? Or are there electric units that I missed?









User #57461437704 posts

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