Using a tankless water heater for water changes?!?!?!

[zachrabbit15]

So was setting out in my fishroom today. I'm planning on switching the tanks to the other side of the room and when I do, the plan is to drill all the tanks for a central drain system to help outomate my 50% water changes. That part is easy but having 400+ gallong of up to temp water to refil with is not quite as easy. I'm very lucky that we are in a very nice little vally with a well. My water comes from the tap at 5.5ph and 60ppm TDS so I don't need to really age or treat my water. I'm adding a shop sink to the room and will be teeing of the main water line feeding my current water heater. While at Home Depot I started looking at the Tankless water heater systems and it got me thinking.

CVould I just run a tankless water heater system to heat my water *** I fill the system after water changes?

Any and all thoughts appreciated. Thanks Zach

[nc0gnet0]

No.

[nc0gnet0]

....I could go into all the technical reasons why It's not a good idea if you want me too......I looked into them a couple of years ago myself for almost the same reason ( a little more water). Your much better off going with a power vented 40 gallon hot water heater setup to be used just for your fish needs.


-Rick

[zachrabbit15]

That doesn't really give me much reasoning? We have one on the house now and with the thermostate I can control the temp from 84deg to 115deg, playing with it today, the temp does not fluctuate more than 5deg while filling a 90g tank. Our old 50g electric tanked water heater would run out of water before I was finished with water changes in my old 120g (60g water change). As for vented we are not set up for gas and getting set up in Washington, lets just say its not going to happen.

I'm not arguing that it will not work, but I do want to know why it wouldn't :)

[nc0gnet0]

As for vented we are not set up for gas and getting set up in Washington, lets just say its not going to happen.


Ouch, that really sucks! Back two years ago when I was researching this (and I was, like you ready to pull the trigger on going with an on-demand hot water heater for my fish room) the biggest reason for the change was going from electric heat to natural gas (a much cheaper option). A lot of my knowledge on the mater therefore applies to the natural gas units, but, there are going to be areas which are common to both.


the temp does not fluctuate more than 5deg while filling a 90g tank

that is getting awfully close to my comfort range in regards to temperature fluctuation. fine for adults and decent size juvies, anymore than that and it could be an issue with young fry/wigglers IMO.


Our old 50g electric tanked water heater would run out of water before I was finished with water changes in my old 120g
How fast your hot water tank runs out of water will be a factor of the temperature of the water in the tank, how fast it can heat the water to temp, and what the ambient temperature of your tap is.

Ok, back to the tankless water heater:

Fact: on an average household with average water usage, they are more efficient than that of a tank water heater
Fiction: On demand hot water heaters are more efficient at heating the water. Not true, they are actually less efficient at heating the water, but they more than make that up by not having to continously reheat the water in the tank to keep it up to temp. This advantage lessens with the more water you need to heat

problem: Your heating needs are going to be far from typical, not may people take 400 gallon hot showers etc. These units are not designed for that type of usage, and you will find yourself literally burning them out as a result. Take a drag car running nitrous, designed to run in 1/4 mile blips. Works fine when properly implemented,,,,,,,,but can you take that car out and run it in the indy 500.......nope.

As a result, your going to be replacing more heating elements on your unit, doing more maintenance (and the parts are costly) and you will never hit the break even point over a tanked water heater.

So, if the question is will it work, I guess the answer could be yes, but if the question is would it be cost effective, the answer is no. You did throw me a curve by not having natural gas however.

Are you running your water change water straight from the tap, no storage tanks etc?

[zachrabbit15]

Right now I use a old 120 acrylic to fill/heat/transfer water for water changes. As I bring more tanks on-line the 120 is already maxed at this point. Space is somewhat limited in my room, consession to my fience :), soadding more water storage is very limited. What I am trying to eliminate is having to use space to store water.

The unit I'm looking at is not cheep but is a commercial unit for running 40gph at max temp 130f continuis duty ($1800 german built). So not a cheep inverstment, but neither is having 20 or so prs of discus.

[DLock3d]

Really glad I opened this thread. I've thought about this before myself. Fortunately, I never pulled the trigger.

[nc0gnet0]

The unit I'm looking at is not cheep but is a commercial unit for running 40gph at max temp 130f

Assuming your ambient temperature of your tap is 55, that means you will roughly have 90 gallons of hot water per hour to do water changes. So, with your uber expensive on demand hot water heater it will take you more than 4 hours to do water changes....better pack a lunch. And thats at running your unit at maximum rated capacity for 4 continous hours (going to need a setup to mix hot and cold water and keep it regulated also.

Your going to have to face it, to do 400 gallons of water changes a day, your going to need to take a good hard look at upping your water storage somehow. However, you could go with 2-3 on demand hot water heaters and cut your time down in half or a 1/3.

[zachrabbit15]

Your looking it at as running 130f max temp 100% duty cycle, at 80f, it is running 40% duty cycle and will run over 300gph. For a note I keep mine at 87f. So a hour and a half at the most.That means I can drain one set of tanks (3x75g), clean them, and start refilling them whlle I move on to the next set. Also as for ware on the unit it is one on/off cycle per day instead of 20 5-20min on/off cycles, it is rated at a contunius on at 100% duty cycle for 2hrs. Like I said not a cheep unit plus has 10yr warrenty.

[nc0gnet0]

Your looking it at as running 130f max temp 100% duty cycle, at 80f, it is running 40% duty cycle and will run over 300gph.

And your talking to sales people and information brochures, whereas I talked to field technitions and installors ( I happen to be in a related field that works hand in hand with many different heating and cooling companies). And in my example, while yes I am running max temp, that does allow me to use another 60 gph tap (unheated). I would double check to see if like you say at 40% duty cycle, the unit can actually handle a flow rate of 300 gph. To get that kind of flow rate through the small diamter internal plumbing of the unit, your going to have to have some pretty decent pressure at your tap.


Also as for ware on the unit it is one on/off cycle per day instead of 20 5-20min on/off cycles, it is rated at a contunius on at 100% duty cycle for 2hrs. Like I said not a cheep unit plus has 10yr warrenty.

Is that an anti-leak warranty or does the warranty cover the heating element as well? Check that carefully. Which unit are you looking at, one of the Stiebels? Also be aware your going to need to hire an electrician to wire this thing up, and stand a good chance of needing some upgrades to your electrical service box (these units require 150 additional amps of service). You will also need to get a flush kit for the unit, which runs around another 200 bucks.

Good luck, you sound fairly convinced. Initially I am sure you will be quite happy with it (until your electric bill comes) but, the proof will be two years down the road. I was suprised to see the price has come down as much as they have, when I was looking into them they were closer to $1800.

[nc0gnet0]

So Zach,

Did you pull the trigger on this venture? Curious how things are working?


-Rick

[ganesan]

I never keep a heater in my ageing barrel as when I do daily 25% WC the temp of aquarium never changes significantly. May be its because I live in the tropics where the temp of the atmosphere is around 90 to 100 F