Author Topic: Dual Flush Toilets Save Money?  (Read 521 times)


  • 5 O'Clock Shadow
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Dual Flush Toilets Save Money?
« on: July 05, 2018, 12:25:44 PM »
Just thought I’d share some math for others who might be wondering the same question that I was – do “dual-flush” toilets save money? In short: No.

Cost of water: I pay $4.63 per cubic meter including sewage = $0.00463/L ($0.001223/gal)

Assumed usage: 4 regular flushes per day on a regular toilet, versus 1 “solid” flush and 3 “liquid” flushes per day on a dual-flush toilet. This is for my master bathroom so it normally is only used when getting ready in the morning and evening.

American Standard: I’ve had bad experiences with cheaper toilet brands so I consider these pretty minimal.
Model 1: American Standard Reliant 4.8 LPF Round Front Toilet ($138.00)
Normal flushes per day: 4 x 4.8L = 7008 L/year
Cost per year: $32.45

Model 2: American Standard Cadet 3 2-Piece 6.0 LPF Dual Flush ($268)
“Solid” flushes per day: 1 x 6L = 2190 L/year
“Liquid” flushes per day: 3 x 3.8L = 4161 L/year
Cost per year: $29.41 ($3.04 saving)
Payback period: 42.7 years (bad investment IMO)

Glacier Bay: Home Depot’s store brand. YMMV, personally I avoid them.
Model 1: GLACIER BAY Premier 2-piece 6.0 LPF Single Flush ($98)
Normal flushes per day: 4 x 6L = 8760 L/year
Cost per year: $40.56
Model 2: GLACIER BAY All-In-One 2-Piece Dual-Flush ($144)
“Solid” flushes per day: 1 x 6L = 2190 L/year
“Liquid” flushes per day: 3 x 4.1L = 4489.5 L/year
Cost per year: $30.93 ($9.63 saving)
Payback period: 4.7 years (maybe worth it if the toilet lasts this long)

In both of these cases I’d be wary of the more complicated dual-flush toilet lasting long enough to save money.
Why bother to do math like this? I was actually tempted to “invest” in the $268 American Standard dual-flush before now. Instead I’ll get the simpler Relient model now and save $130. Am I overthinking this? Almost certainly, but that's my style!


  • Walrus Stache
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Re: Dual Flush Toilets Save Money?
« Reply #1 on: July 05, 2018, 02:30:52 PM »
Savings on water is not the driving force behind dual-flush toilets.  as you noted in most municipalities water is so cheap that the ROI can be decades.

the real reason to use a dual-flush vs. traditional toilets is if you give a damn about the environment.
You could make (and others have made) similar calculations about using disposable plates vs. normal reusable ones, about the 'cost' of plastic straws (about as much as for the soda it displaces) etc.

tl;dr - it's not about the money.

full disclosure: i have dual flush toilets installed since 2012. My personal opinion is that all renos and new construction homes should install them as a matter of principle.
"Do not confuse complexity with superiority"


  • Handlebar Stache
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Re: Dual Flush Toilets Save Money?
« Reply #2 on: July 05, 2018, 04:35:19 PM »
It is also important to note that not all of us live where water is cheap -- our water rates start at $0.0089/gallon, and go up from there; that's nearly 8x what you pay! Unsurprisingly, yes, dual flush toilets are extremely common where I live.

Although I agree generally with nereo here -- even if you don't live in a place with expensive water, there's still an environmental case for using minimal amounts of (fresh, clean, drinkable!!!) water to flush your toilet.


  • 5 O'Clock Shadow
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Re: Dual Flush Toilets Save Money?
« Reply #3 on: July 14, 2018, 06:56:59 AM »
I live in a rural area with well water and a holding tank for septic.  So we have no water bill but we pay about $400/yr to pump the holding tank (multiple pumps @$80 per pump).  We bought the dual flush toilets to try to reduce the water going into the holding tank so we could pump it less.  We got the Eljer brand toilets for both of our bathrooms.  I think they were fairly cheap at Menards.  We've had them for over 5 years now and they've been great.  No issues. I think it's something like 0.6 gal flush for "liquids" and 1.6g for "solids".  I don't have definite proof that they reduced the holding tank pumping at all but they've been good toilets.

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  • Bristles
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Re: Dual Flush Toilets Save Money?
« Reply #4 on: July 14, 2018, 07:47:21 AM »
My last house was a 1955 custom built mansion monstrosity that had its original by-god toilets that had an enormous tank.  They were champagne beige and it was like the tide going out with each flush.  Of course, the original owner also had by-god chandeliers in the master bathroom.  We were only the second owner and the original folks had lived through the Depression and very much compensated for the earlier life's privations.  Much remodeling ensued but we didn't choose the dual flush stuff, just modern, smarter appliances as the standard replacements.  We put in enormous amounts of insulation and replaced many leaking windows.  We left it in much, much better shape than how we found it from an ecological perspective. 

Alternatively, the house I moved into last fall is a 1938 house and the prior owners lived there 25 years.  I knew both the husband and wife coincidentally due to my profession and had seen articles the hubby had written in the local newspaper advocating for a carbon tax initiative.  Super tree-huggers you could say, and very concerned that you saw how tree-huggy they were in their public lives.  In this house they had a new electric car charging station installed and a 100% organic garden (both proudly noted in the listing for the house). 

However, the furnace was from 1960 and had an original, manually controlled mercury switch thermostat.  The back door was literally rattling in its frame from lack of weatherstripping.  They had zero window coverings on the original wood windows (testimony from the neighbor about the nightly show, no curtains on bedrooms and baths, ever.)  Also, they left the master bathroom window open 100% of the time because there is no vent fan in that room.  As another annoyance the dishwasher sounded like a cat was screeching every time you opened or closed the door though that is not really an environmental crime other than noise pollution. 

On day #1 after the movers left I installed a $35 digital thermostat and installed $3 worth of weatherstripping (and ordered the $12 DW door balancing parts that fixed that goddamn dishwasher).  Over the winter I installed heavy curtains and the draft reduction was instantly noticeable.  Many times over the last 7 months this house has made me fucking angry but I have just worked through the list, including a new 96% efficiency furnace.  Clearly the prior owners invested a lot into their image of being earth mothers but neglected to do the things that could make real, daily, huge differences in their energy consumption.   

The point I am making is that a lot of the green technology around is sold to those who want to look green.  You don't get an article in the paper by updating the 60% efficiency furnace to a 96% one-- well, maybe the reporter will call me today-- /snark.  Cue the South Park episode featuring the Toyota Pious with its emissions of Smug rather than smog.     

I worked at a fuel cell company for a few years in the early 2000s and that company (in business since 1996) has yet to make one nickel of profit.  But the research must go on and hopefully the technology will catch up.  Don't forget that bottled hydrogen comes from cracked natural gas.  And the car charging station is powered by a coal and natural gas generating station.  Right now the cost of the materials and production effort far, far exceeds any perceived savings, but as I said that is not the whole point.

All that said, I do advocate that new homes have fixtures installed that are the smart and efficient as a matter of standard practice.  And the cost for things like dual flush will come down over time because they are standard.  Install enough of them and in places where water is not plentiful it does make a difference.  But don't feel guilty for doing the math and deciding a retrofit is not a good option.     


  • Magnum Stache
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Re: Dual Flush Toilets Save Money?
« Reply #5 on: July 14, 2018, 05:36:34 PM »
I installed the $20 dual-flush kit from Big Box. It's worked fine in my low-flow toilet for years.

Professor Toilet doesn't like them,

but it's important to remember that using button #1 is for liquids and #2 works the same as the toilet did previously. Payback was less than a year.