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Water heater for darkroom...tank or tankless

Dave Swinnard

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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
 
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.
 
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.
 
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.
 
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.
 
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.
 
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.
 
About 5 years ago I worked in a lab that had a gas tankless water heater and we had nothing but problems maintaining 70 degrees for B&W processing. When I built my darkroom I put in a 19 gal electric hot water heater in and has worked well. The only thing I would do different is a bigger one (40 gal).
 
My experience is that a tankless heater doesn't work for darkroom applications, there is no buffering with regard to flow rates for example. I eventually went for a 4.5 kW 15L dedicated unit that can re-heat with enough power to provide hot while still under load. The 3 kW units cannot do this. However, a large tank would work fine provide it isn't depleted.

Tom
 
Minimum low flow rates. Of course, go figure. Thanks for the cogent discussion, everyone.
 

Hi Michael. This is good information.

Can I ask why you feel you need a larger tank? Do you routinely run out of hot/warm water during your normal processing situations?
 
In my last darkroom, I put in a 10 gallon electric tank. It proved to be useless as I didn't turn it on unless I was working in the darkroom, and then it took too long to heat, and then ran out too soon. My current darkroom is plumbed for a heater, but I have yet to install one. However, I'm in Texas and you're in Canada, so things are different.

If and when I do install a heater, it will be a standard 40-50 gallon model, which I have seen used successfully in other local darkrooms. In all the years I've been on internet forums, I not heard much good about tankless in a darkroom situation. It's the flow rate.
 
I have tankless hot water in my entire house, not to be confused with instant hot water. This includes tanklesss in the darkroom. Works great, I love it. Mine runs on propane. Bill Barber
 
You could move to Texas where you really don't need a water heater most of the year. Bill Barber
 
I wonder about having a tankless heater that is used to fill a tank heater that is only used when you are working in the darkroom.

Or two smaller tank heaters in parallel.
 
I'm a plumber. Save yourself a lot of potential headaches and get a minimum of a 30 gallon water heater.
 
We have a whole house gas fired tankless water heater, at the low flow rates appropriate for washing it doesn't come on.
For the darkroom I have a small point of use tank heater on the hot line that takes care of that problem. It's only 2.5 gallons, so it's easy to run it out of heated water if I'm using a lot of water, but it isn't a problem for normal use. It runs on 110 power, so that makes things easy.

For a point of use tankless heater you would want to look at what its minimum flow rate is for activation. My recommendation would be a point of use tank water heater if power and space aren't issues. Though, the 10 gallon and smaller ones will fit pretty much anywhere.
 
mopar_guy said:
I'm a plumber. Save yourself a lot of potential headaches and get a minimum of a 30 gallon water heater.
Click to expand...

This. I've put in a LOT of tankless systems - mostly gas-fired - and they do a great job of heating water very quickly, but a tankless heater by itself is not going to be a good system for a darkroom that requires large amounts of 70°-ish water unless it has a low-flow, low-heat capability. The amount of hot water that most faucets or tempering valves will draw in order to create the water temperatures that we want in a darkroom is almost non-existent, and that low of a flow at temperature is usually only reachable by having a system that maintains a reserve tank. Simply put, most tankless systems can't provide this small of an amount of heated water without 1) a reserve/holding tank and/or 2) a circulating pump in the mix, the price of which makes the entire system stupidly expensive and still not as functional as the "normal" way of heating water. Thus, I'll back up mopar_guy and suggest a conventional electric heater. Personally, I'd put in a 50-gallon because they're usually about the same price as a 40, and both of those are less expensive than the 30-gallon models in my neck of the woods...and come to think of it, that's exactly what I did.
 
The local HVAC dealer says the new tankless are the most efficient available. No heating water all day for the few bits of time you use it. When we were in Portugal we had propane fire tankless. Could set the temp and flow at the heater. Grease pencil marks for each family members preferred shower temp. For my 54 degree F ground water temp it would take an electric tankless about 2 KW an hour to provide 68 degree F darkroom water. Can you say 20 amp breaker. (for a gallon a minute flow). If you can go to a low flow then tankless electric is the easy on the budget direction.
 
What are you going to do with the hot water? Why not buy a Jobo instead of a water heater. The Jobo has the heater built in. In my darkroom I use tempered water only to fill the Jobo (convenience) and to mix Dektol (as mentioned above).
 

Thanks Sundowner and all you others who've provided feedback. This is exactly the sort of experienced based information I knew would be forthcoming from this diverse group of folks.

I will go with a tank unit, power is already there. but I'm afraid I'll have to go with a 20 gallon based on size constraints. (it's that or just cold water...)
 
ic-racer said:
What are you going to do with the hot water? Why not buy a Jobo instead of a water heater. The Jobo has the heater built in. In my darkroom I use tempered water only to fill the Jobo (convenience) and to mix Dektol (as mentioned above).
Click to expand...

I already have a Jobo and it does a fine job of tempering my film processing liquids, but for print washing and some of the alt processes I want larger quantities of running, tempered water available.

As I have an opportunity to build (though on a tighter than I'd wish for budget, but that's what retirement gets me) my first designed-by-me darkroom, I want to have hot water available when I need it.

Having spent the money to have drainage and water run out back to the garage, and agreement from the wife to use (a bit less than) half of the space, a hot water tank is not a big stretch financially. I expect this to be the last (and first) time I get to put a darkroom together with "wants" and maybe even a few "nice-to-haves*" instead of making do with re-tasking available spaces other people's ideas of darkrooms.

* the Jobo and an Expert drum was one of the biggest "nice-to-haves" I ever got to have in my darkroom.
 
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