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  #1  
Old 24th February 2014, 08:03 AM
Jeff Sheff Jeff Sheff is offline
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Default Darkroom Water Heater

I am just in the process of fitting a new sink in my darkroom and while I've got the pipework stripped down I thought I would fit a hot tap.

My initial plan is to use one of those instant heaters that fit under the sink and warm the water as it passes through. This would of course give me hot water but what I would like ideally is mixer based one so I can wash my films in the middle of winter. At the moment I use my Jobo but decided to go back to washing by hand hence the need for a regulated water temperature of about 20c.

Any ideas would be welcome.

Jeff
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Old 24th February 2014, 10:08 AM
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A good one is not cheap. Problem is temperature accuracy at any flow rate and ability to adjust it finely and be able to see what the temp is. These aren't cheap but are one of the few that give you an led read out and will work for colour temps too. And the right model will go down to 20degC, some won't.

http://www.stiebel-eltron.de/en/priv...hlauferhitzer/
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Old 24th February 2014, 11:06 AM
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Instant heaters need quite a big flow rate to work properly otherwise the element will repeatedly shut down and you'll get a very inconsistent temperature. To provide a mixed flow at the rate required for film washing would mean a very low hot flow rate so I suspect that type isn't going to be very successful. I think you probably need some form of local hot water storage, maybe one of those wall-mounted heaters that store a few litres might work. One of these for example:

http://www.heatraesadia.com/express/
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Old 24th February 2014, 11:28 AM
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There are these but again not cheap

http://www.hassmfg.com/search.pl/139...&submit=Search

As you can see keeping water temp constant at a given flow rate doesn't come cheap plus you need a hot water feed.

Another idea would be to use an emersion tank with thermostat set very low. But do you have the space or want the hassle of an emersion tank.

When I looked at it (didn't do anything about it) I concluded that the Siebel units were simplest, smallest and probably about the best it was possible to make happen with ease of use and accuracy. But not cheap and you do need the one which allows 20degC.

And as Richard has suggested you would need to check with Siebel what the minimum flow rate is before it shuts down. But it does have the benefit of delivering water at correct temp for development purposes.

Last edited by Argentum; 24th February 2014 at 11:36 AM.
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Old 24th February 2014, 11:37 AM
TonyMiller TonyMiller is offline
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Could you pipe the cold to an electric shower on the wall and run the shower hose from that as a mixer providing a steady 20°c? There's usually a 2nd hand one going on ebay
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Old 24th February 2014, 12:20 PM
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I suppose the question ought to be, what is the required flow rate range for print washing? Without that information it's impossible to determine which type of unit will do the job.
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Old 24th February 2014, 12:43 PM
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The Sadia unit I linked to has a "Thermostat adjustable from 5°C to 75°C" and as it stores up to 15 litres of water temperature variations at a low flow rate should be minimised.
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Old 24th February 2014, 01:12 PM
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well yes but as water is used from the sadia unit it will be replaced by cold from supply. At start of flow it won't make a difference but with a constant flow 15 litres will be replaced how quickly and will the heater heat it at quick enough rate to keep the temp constant?

All depends on flow rate and heating rate which will also be dependant on temp of cold supply.

how much water is used in 30 minutes of print washing ?

I asked Stiebel about flow rate. Answer is that minimum rate to activate heater element is 2.5 litres a minute but at 20degC the heating element may cut in and out meaning temp may not be constant at that slow flow rate.
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Old 24th February 2014, 05:12 PM
Tom Kershaw Tom Kershaw is offline
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An instant heater will not work. Suggest going for a small storage model as suggested by Richard. My Heatrae Sadia unit is a 4.5kW / 15L model. The 4.5kW is useful as the tank can be reheated while warm water is in use. A 3kW model may not be able to reheat the small volume of water fast enough.

Tom
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Old 24th February 2014, 05:38 PM
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Quote:
Originally Posted by TonyMiller View Post
Could you pipe the cold to an electric shower on the wall and run the shower hose from that as a mixer providing a steady 20°c? There's usually a 2nd hand one going on ebay
That would be my approach as well.
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