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  1. #1
    Dave Swinnard's Avatar
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    Water heater for darkroom...tank or tankless

    I am building a darkroom in an external garage - drainage and cold water have been run. Now I need to address the issue of hot water (electric). Looking at options it appears that point of use tankless systems are less expensive than the small tanks I've seen. I have both 110 and 220V available in the garage.

    So my question to you folks is: has anybody used a tankless, point of use water heater in a darkroom situation? If so, does it supply your needs adequately? Are there any gotcha's? (I've only ever had experience with tanked systems)

    Dave

  2. #2
    mr rusty's Avatar
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    Tankless systems will be instant heaters and will almost certainly require a lot more power. While you may have the voltages available are your cables up to it? In the UK standard cables from sockets are good for 3kW. Anything above that and you need a separate cable run.

  3. #3
    Dave Swinnard's Avatar
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    Quote Originally Posted by mr rusty View Post
    Tankless systems will be instant heaters and will almost certainly require a lot more power. While you may have the voltages available are your cables up to it? In the UK standard cables from sockets are good for 3kW. Anything above that and you need a separate cable run.
    I can run cables from the sub-panel in the garage if necessary.
    It was a 3kW unit I was looking at. My major unknown is whether the unit will supply the water I need for the durations involved in the washing steps...tempered water for long(ish) durations, i.e. low flow situations.
    I have exactly zero experience with such units.

  4. #4
    ROL
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    I would also like to hear about people's experiences with tankless for the darkroom. On the face of it, they would seem to be a great option for point specific use, all other factors being equal – which they're not. Pragmatically however, most B/W processes only require water temps controlled to 20ºC, not much to warm water even in the winter where I live. Mixing Dektol is the only time I need "hot" water, except when cleaning up. FWIW, I tied into an existing gas fired tank system, and have never wanted for correct water temperature (adjusted through water temp control panel). It appears to me if you are starting from scratch with an independent system that requires electric to start with, a tankless would be ideal. Sorry, I can't be of more help, but please report back, especially if you're the guinea pig.

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    I had a similar situation with my darkroom - I was worried that since the instantaneous power drawn by a tankless system would create a big power draw, and potentially dim my enlarger bulb, I opted for a small conventional heater. The heater that I have is ~5 or 6 gallons, and is powered by 110V - it sits under a bench and seems to work well. If I had gas in the garage, I probably would have opted for a gas powered tankless system.
    I don't use a lot of hot water in the darkroom, mostly just to mix with cold to bring the temp up to 20C, so a small capacity heater works just fine. I turn off the heater when I am not using the darkroom.

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    I will preface this by saying I looked in to these quite some years ago, but, flow rates were the problem with the tankless variety when I did. I'd pay close attention to those numbers and figure out your flow rate (of the hot water) carefully. If you're running through a mixing valve and you only use 20% hot water to get to 68 or 70 that is a very small amount of water volume, which might not be sufficient to trigger some units into action. I'm a fan of a well insulated hot water tank, and insulated hot water pipes.

  7. #7
    L Gebhardt's Avatar
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    I have played with two models of gas tankless heaters and I find I can't get a low enough flow rate for darkroom use. At low flow rates the burners turn off, giving you only cold water. I imagine the electric ones may be better in this regard, but I haven't tested them. I now use a heat pump water heater (50 gallon tank) for the house and darkroom. It's much cheaper to run than the propane tank heater. But that's not going to be worth the expense for a heater that's only used for the darkroom.

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    Quote Originally Posted by L Gebhardt View Post
    I have played with two models of gas tankless heaters and I find I can't get a low enough flow rate for darkroom use.
    The ones I investigated were gas as well. No experience with electric models either.

  9. #9
    Dave Swinnard's Avatar
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    Quote Originally Posted by L Gebhardt View Post
    I have played with two models of gas tankless heaters and I find I can't get a low enough flow rate for darkroom use. At low flow rates the burners turn off, giving you only cold water. I imagine the electric ones may be better in this regard, but I haven't tested them. I now use a heat pump water heater (50 gallon tank) for the house and darkroom. It's much cheaper to run than the propane tank heater. But that's not going to be worth the expense for a heater that's only used for the darkroom.
    Larry, the cold water at low flow rates is my biggest concern. I wonder if the electric ones have the same issue. I am digging about on the home renovation forums but haven't found my answer yet.

  10. #10

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    I'm looking at the Rheem RTE3, basically the smallest electric model I could find. 120v, minimum flow of 1/2 gallon per minute and an external temp control. I'm gonna guess that 1/2 gallon per minute is the ballpark minimum of anything out there.

    The gas unit we had was useless even for the shower, with the new water-conserving shower heads, have to turn on hot water in the sink in addition to the shower to activate the heater. Ended up with an electric 5 gallon tank in the darkroom, which I was not totally happy with, particularly in cold weather.

    This Rheem is designed for a bathroom sink or the like, and seems like it would provide 70-80f without wasting too much water or electricity. I think it has a 30 amp breaker, so you could probably fashion it to be able to plug into the wall instead of hard wiring.

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