+ 1 Votes Not Enough Info dogknees 3 years ago The electrical connection should make no difference. In parallel they each get half the current but the full voltage, while in series they have the same current, but half the voltage. Since power is the product of voltage and current, the two arrangements give the same power. The water is the hard part. If, for instance, they raise the temperature of the water by 50 degrees C, and that the water enters at say 10 degrees, in series the first one would heat it to 60C. But, the second can't raise it another 59C as that is over the boiling point of the water, and it takes more energy to actually boil it. The effectiveness is also dependant on the water temp entering the unit. The heat flow is dependant on the difference in temperature between the heating element and the water. As the difference goes down, so does the rate of increase. So, you need to know, at least, the temperature of the water at the start and the maximum temperature of the heating element in the heater. You would also need some more information about the efficiency of the heating elements and the rate of heat flow from them to the water as a function of the rate of flow. + 0 Votes To all that care to see a better diagram... Benny7440 3 years ago I didn't know that Google Docs had a better (simpler) drawing api there until yesterday, so I took the time to re-draw everything again, but this time in just one diagram you can see all four combinations. Hope this help a little. The link: https://docs.google.com/document/d/1q3uKjinjeah1wRfUFi7So8qQFUeYdDcnV03IZS6jaP4/edit?hl=en&authkey=CKDJxaoO Thanks indeed to all that have responded! + 0 Votes I might be missing somethingm, but Tony Hopkinson 3 years ago If the heaters are "equal" There are only two combinations, series and parallel In series Heater 1 is going to do it's stuff then heater 2, bearing in mind heater2 is going to work on heater 1's output. There will be some change in flow, don't know whether you can discount non-linear effects either. It effectively takes more energy to raise a volume of water from 30 - 40 degress than 20 to 30. In parallel, each one is is going to get half the flow... + 1 Votes What "4" combinations? oldbaritone 3 years ago As Tony said, there are really only two combinations, series or parallel for the water. If you're thinking about mucking with the electrical supply - don't! It should be connected the way the manufacturer specifies. So don't even think about trying to hook the electric supplies in series; you'll create a serious risk and it's completely avoidable. Ground Fault protection as specified is essential too. You don't want someone in the shower to get zapped. Have an electrician do the electrical connections for you, so they're done properly. Your comment "... and they don't have a thermostat ..." also is a concern. Are these heaters approved for residential use, or is it some industrial unit? Without a thermostat is there the possibility that they will produce scalding-hot water that may be dangerous in the shower? And as dogknees mentioned, if they're in series the water may be dangerously hot all of the time. Usually, putting industrial equipment in a residential application is a no-no. All of that being said, parallel will give you more flow rate, at a lower temperature. But if the shower is on low, the parallel configuration might not have enough flow rate in each unit for the sensor to turn the heat on. Series will give you a higher temperature, at a lower flow rate. But "higher" might be dangerously so. Given your question, it sounds like you should bring professionals in to review and make recommendations for you, not just post vague questions on a blog. Someone might get hurt if this is done improperly. + 0 Votes Thermo ... Charles Bundy 3 years ago homework or is this a real world application? You might try http://www.gdn.edu/PT_Faculty/cmckeithan/1011_6thru8prob.htm Which has a bunch of fluidic and thermo problems/solutions. Hope this helps! + 0 Votes This is most certainly a homework problem robo_dev 3 years ago In home plumbing, there are at least a dozen reasons you don't put things like heaters in parallel or in series, nor do you typically have more than one. If your goal is to heat the water, then it would be logical to have a recirculating pump of some sort. A typical 'on demand' electric hot water heater is not suitable for use for a shower, as it does not provide enough hot water fast enough. The only tankless models that can do this are gas-fired units..... + 0 Votes OK maybe I'm missing something here OH Smeg 3 years ago But when you say in Series or Parallel are you talking about the Electrical Connections, The Water Connections or both? Frankly I can see no benefit for feeding one heater with the output of another so here I'm assuming that they are feeding different showers and you want to know how to wire them in. This is a basic Electrical Examination question and if you can not answer it you are not qualified to be considering doing the work. For a complete answer read and learn the contents of your Text Books that is the best answer that I can give you so you will learn these things. Col + 0 Votes orfice upstream of switch. goodsellus 3 years ago for size on your own. jg + 0 Votes To difuse all the smog Benny7440 3 years ago First of all, lets say thank you all for responding! Now for the specifics... I- To dogknees: If you consider that in parallel the current is half you're wrong. 120 Vac is what's coming from the grid & if in parallel they both receive that voltage. When in series they both experience half of the previous current since they're equal in resistance & power rating (wattage). Think of it as if they were 2 equal bulbs: in parallel they both shine with the expected luminosity; but if in series they might even fail to give any apreciable light (half of the current of any of the previous bulbs & half the voltage, so one fourth of the power for each). In your 2nd paragraph you really gave me a valuable tip referring to the specific heat of water, something that I hadn't considered yet. The last remark is very tied to your 3rd paragraph. It's clear for me that you're right I need more specifics on the circumstances... II- To Tony Hopkinson: The following link may serve as a clarifier: https://docs.google.com/leaf?id=0B7H8_cPT-BwdNzdkOWVjMTEtMDAyNy00ODI0LTliZDMtZGMwNTM5OTk3N2Fm&hl=en Also, the amount of heat in a certain quantity of water will affect heat transfer ratio (a valuable tip)... III- To oldbaritone: The following links are intended for clarification: http://tankless-water-heaters.ecrater.com/p/1450643/marey-aquamatic-2-electric-shower-tankless http://www.inspectapedia.com/plumbing/Electric_Shower_Heaters.htm The last one contain a picture of the exact type I'm referring to. Sorry for the lack of info in my original post but, as I mentioned right there, this site doesn't offer the possibility for uploading attachements/diagrams. I did mention this there & also that I had the diagrams already prepared so you had the possibility to ask for them instead on insisting in judging what, for you, was already blurred... IV- To Charles Bundy: Those links were very good & interesting. By the way, this isn't any homework even though I have had those heaters around for quite a few years now; but in a sense, it's a home 'work' but not any assignment from any school or university. It's a personal thing/idea/project to be dealt with any time in the future. That time might be right now, though! V- To robo_dev: I'm sorry to tell you but you're wrong twice: isn't a homework (if I'm understanding 'homework' correctly, it's what you bring home in order to work it out & presenting your results to the teacher/professor). I'm not a student, I'm curious! Next, we have had in this house for more than 30 years those kind of water heaters (electrical). I'm not sure where they come from but all my life suppossed that it was something in the category 'Universal knowledge'. I mean that I always suppossed that everybody else new about them... VI- To OH Smeg: Yes, you're right! You're missing a few things. Have a look at the diagrams... + 0 Votes More fog diffusion needed... Benny7440 3 years ago Thanks, Tony Hopkinson, for responding! ...Going from a general sense to the more specific one. This whole thing of starting this discussion was aimed at ending with a clear understanding of the effect of the different configurations, in a purely theoretical sense, of the output water temperature. In relation to your second sentence/first paragraph, Tony, I guess you're referring to, say, current (I) or water flow, each of the units receives half of the system total. Next sentence, 'full current flow' (for both water & electrical current) of the whole system; but, in relation to the previous configuration it makes little sense. It would have been helpful to use a standard way of measuring electric current & water flow, for comparison purposes (i.e., Amps = I(total), I1 & I2 & I1+I2 = I(total) & GPM = Gallons Per Min.). The end of that sentence seems to be a contradiction: ...'get half of the time to apply it' is referring to what, precisely? If the flow is for all configurations equal at the input stage then, when in series, the water will have double the time within the confines of the heating enclosures. Seems to me that your last post is difficult to grasp, sorry. + 0 Votes Nope Tony Hopkinson 3 years ago If split one flow into two, you get half in each, same as if you split one current into two you get half in each. If your heaters had a capacity of one liter and you had a flow of a liter per seond. In series each heater has each litre of water for one second to work on it, in parallel two... Taking your measurements at the wrong point there, when you join them back together you get 2 * half a litre per second.