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Instant water heating anyone?


crossley

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Will be going to the crick show this weekend, with an eye to what is available in on demand water heaters. I have the usual set up, a little wenlock back boiler stove gravity feeding a radiator in the fwd saloon done in 28&22 mm copper,  and a calorifier coil by gravity too. Plus two rads on a 15mm pumped circuit going aft. Now the fwd rad has  always worked all too well, but the hot water takes hours, I don't think the circulation is that good, it only being an  1/2" or so coil. So I have to either roast in the saloon for hours, run the main engine, or boil a kettle to get hot water. I'm not particularly keen on instant gas heaters, what with all the faffing about with special flues, and room sealed this and that, but what other options are there? I quite fancy the little webasto, but how to heat the fwd radiator as it's on the other side of the back boiler? A small dedicated heater just for hot water, showers etc, is just what I'm looking for. I don't have a shore supply, but can run the 1 kw immersion heater off the inverter, if need be, I have a big bus 24v alternator that copes easily with this, but it means hours on the engine. 

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Maybe, yes. Is there a modern instantaneous water heater that I could be having a look at whilst at the show,?maybe something new to me, I have given details of my installation so others can advise of a suitable unit, should such a thing exist. The gas boilers are I think going to be the quickest form of heating, but the choice is limited to the room sealed units now I'm told. 

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Morco D61 is the usual one, there's a couple of similar ones on the market so worth googling prices before going. On liveaboard it needs to be installed by a registered gas bod or can be installed DIY (ie not 'for reward') by someone as competent as the gas bod should be.

The calorifier heating from stove could be greatly improved with a plate heat exchanger (£35-50) and a couple of small 12V DC pumps (£13-25 each), maybe figure up to £100 all in. These are the sort of thing:

http://www.ebay.co.uk/itm/Hrale-Stainless-Steel-Heat-Exchanger-10-Plates-max-22-kW-Plate-Heat-Exchanger-/331858113137

http://www.solarproject.co.uk/page2.html

http://www.ebay.co.uk/itm/6-5L-Min-DC-12V-Solar-Hot-Water-Circulation-Pump-Brushless-Motor-Free-Shipping-/232277557088

Seems a shame to use gas for water heating in winter if there's a stove and backboiler fitted and running.

Edited by smileypete
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I don't have a back boiler or calorifier just an instant water heater and it works great - despite what people say about them not working with showers.

Makes life much simpler plumbing wise.

IIRC, the BSS has hitherto allowed them to be installed on boats until a room sealed equivalent becomes widely available.  I don't know enough about the BSS or the market to comment on whether this situation has changed. 

The Morco G11E was about the best of this type last time I looked.  

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On 26/05/2017 at 14:46, Neil2 said:

I don't have a back boiler or calorifier just an instant water heater and it works great - despite what people say about them not working with showers.

Makes life much simpler plumbing wise.

IIRC, the BSS has hitherto allowed them to be installed on boats until a room sealed equivalent becomes widely available.  I don't know enough about the BSS or the market to comment on whether this situation has changed. 

The Morco G11E was about the best of this type last time I looked.  

 

Depends how you are defining 'best'. I chose the Morco D61 as the 'best'. It works brilliantly with my Triton thermostatic shower.  

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9 minutes ago, Mike the Boilerman said:

 

Depends how you are defining 'best'. I chose the Morco D61 as the 'best'. It works brilliantly with my Triton thermostatic shower.  

Another vote for D61 - had ours for almost 5 years and works perfectly for our hot water requirements including a shower.

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4 hours ago, Neil2 said:

I don't have a back boiler or calorifier just an instant water heater and it works great - despite what people say about them not working with showers.

Makes life much simpler plumbing wise.

IIRC, the BSS has hitherto allowed them to be installed on boats until a room sealed equivalent becomes widely available.  I don't know enough about the BSS or the market to comment on whether this situation has changed. 

The Morco G11E was about the best of this type last time I looked.  

Instant gas heaters are great in many guises as are gas fridges I have had variants of both on different boats over the years I would prefer them everytime as main choices but nowadays everything seems to be lectric fed which makes no sense. Changing a few gas bottles is no problem on most boats ( it was a total pain on my Hudson ) this boat is a complete doddle.

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4 hours ago, Mike the Boilerman said:

 

Depends how you are defining 'best'. I chose the Morco D61 as the 'best'. It works brilliantly with my Triton thermostatic shower.  

There was a thread some time ago, maybe a couple of years, where someone mentioned the G11E which is very similar to the D61 but has a much higher flow rate.

Modern thermostatic showers are terrific aren't they, the old mixer valve I had would never work properly but even with the weedy pressure from my Rinnai the thermo mixer works perfectly.

The only drawback with instant water heaters is the gas consumption but I've tried all sorts of systems and I just prefer the simplicity of the instant heater.        

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On 26/05/2017 at 19:51, Neil2 said:

There was a thread some time ago, maybe a couple of years, where someone mentioned the G11E which is very similar to the D61 but has a much higher flow rate.

Modern thermostatic showers are terrific aren't they, the old mixer valve I had would never work properly but even with the weedy pressure from my Rinnai the thermo mixer works perfectly.

The only drawback with instant water heaters is the gas consumption but I've tried all sorts of systems and I just prefer the simplicity of the instant heater.        

 

Yes it has a much higher flow rate, but water and gas on a boat are limited commodities that need conserving. The higher flow rate from a G11 is pointless as it just means using the limited supply of gas and water you have on board twice as fast too.

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I like the idea of increasing the rate of heat transfer between the back boiler and calorifier by using a plate heat exchanger, but it's complicated by needing two additional circ pumps and extra tappings in the calorifier to create a pumped circuit, I'm going to try moving the circ pump first, as I think it's in the wrong place, and put swept tees into the coil circuit where it tees off the flow and return lines. Does anyone be have a little wenlock stove to heat their water? And how long does it take? The actual back boiler itself looks like a proper job, being a full height cast iron thing. On a day like today, an  instant heater would be a boon. I'll be looking around tomorrow, getting some ideas. 

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My bad, posted about the heat exchanger without thinking it through.

Thinking about it the heat transfer capacity of the coil is probably more than adequate for the backboiler, the problem is getting the heat through it efficiently. :) This is probably mostly down to poor circulation, one of those 12V DC pumps should fix that.

But another issue is heat loss in the pipes, especially if the large gravity pipes form part of the pumped circuit. My preferred way would be to tee the pumped circuit in quite close to the backboiler, and insulate the pipes of the pumped circuit between the backboiler and calorifier. This sort of layout:

gallery_2174_346_1611.png

Trouble is the existing may make it tricky to run insulated pipes between calorifer and backboiler, might be possible to box them in at floor level or even under gunnel.

Also with a small pump the pipes should be 'self bleeding' so any un-dissolved air can rise somewhere it won't interfere with circulation, on the pumped part this may be a radiator, or a 'dead leg' with a bleed screw.

If there's good insulation and all the rads can be turned off, then all the backboiler heat must end up in the calorifier, making it heat as fast as poss. :)

Edited by smileypete
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Spent a few hours at crick show today, but nothing stood out, I think for now my instant water heater is going to remain the big copper kettle.. sometimes a little lateral thought pays off, I've found a thing called an "injector tee" which looks promising, and should speed the water through the coil on it's way back to the boiler. They are made esp for mixed gravity/pumped systems. 

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I thought of making something a bit similar but kinda doing the opposite; using the flow from the pump to keep a swing check valve closed and automatically shut off gravity flow.

So when the calorifier water is being heated, all the backboiler heat goes to the calorifier to get it hot as quick as poss. Could also be done with a normally open honeywell valve but they're £££ and need 240V, there are some cheap 12V valves around but would stay closed in the event of failure.

Of course the gravity rads could be shut off manually, as long as they're switched back on if need be, but it's a bit of a faff.

(Ideally you'd want to avoid lukewarm water sitting around too long in the calorifier as it's bad (or good!) for bugs.)

Edited by smileypete
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16 hours ago, crossley said:

Spent a few hours at crick show today, but nothing stood out, I think for now my instant water heater is going to remain the big copper kettle.. sometimes a little lateral thought pays off, I've found a thing called an "injector tee" which looks promising, and should speed the water through the coil on it's way back to the boiler. They are made esp for mixed gravity/pumped systems. 

To be honest if you want the low down on instant water heaters you'd be better off going to a motorhome or caravan show, as that's what most modern instant heaters were designed for.

 

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