What should I know about toilet retrofit dual-flush systems?

Asked by Stephan Pollard
Fayetteville, AR

I'm wondering if it makes sense to retrofit my toilets with dual-flush devices rather than purchasing entirely new US EPA WaterSense-labeled toilets. Are USGBC LEED credits available when using these devices?


Molly McCabe, AKBD, CGP, CAPS

Answered by Molly McCabe, AKBD, CGP, CAPS

Bainbridge Island, WA

A Kitchen That Works LLC

April 18, 2011

Dear Stephan,

Reducing water consumption is always a good idea, but doing so with a dual-flush conversion kit is probably at the bottom of the list of good options.

In an effort to establish full disclosure: I have never installed a conversion kit nor have I knowingly used a toilet that had a conversion kit installed in it.

I am going to assume that your question is geared toward existing single-family residential toilets.

  • With that, there are no LEED points available because there is no LEED program for residential remodels, only single-family residential new construction.
  • My second assumption is that your toilets were installed after the year 2000 and flush at a rate of 1.6 gallons.

A conversion kit would seem to make sense

Given that we typically flush more liquid waste than solid waste, a dual-flush conversion kit would seem to make sense on the surface.

However, in reality it generally does not, for the following reasons:

  • You will likely void the toilet manufacturer’s warranty if you install a conversion kit in your toilet.
  • The design of your toilet most likely requires the full 1.6 gallons to clear the bowl. Therefore you run the risk of not clearing the bowl if you install the conversion kit, and we all know that a dirty bowl gets flushed twice -- no water savings there.
  • Many homeowners do not understand what kind of flushing method their toilet uses; i.e., gravity-fed (wash-down) vs. siphonic. Dual-flush conversion kits are only applicable to gravity-fed models. Therefore, homeowners run the risk of choosing the wrong product.
  • The time and effort to install a conversion kit is greatly underestimated by most manufacturers of this type of product. Realize that with most kits you will have to turn off the water supply and remove the tank from the bowl (two-piece toilets) before you can install the kit.

To the best of my knowledge, there are no domestic dual-flush conversion kits on the market that have been tested by an independent third party to quantify the manufacturer’s stated flush performance. However, most, if not all, kits meet either the ASME A112.19.10 national standard for retrofitting 3.5 gallon toilets or the IAPMO PS 50-2008 standard for retrofitting 1.6 gallon toilets.

Other forms of compliance to look for include: ASME A112.19.2 – “Vitreous china plumbing fixtures” and ASME A112.19.5 – “Trim for water closet bowl, tanks, and urinals.”

On the other hand

Now, if my assumption is incorrect and you have a toilet that was installed prior to 2000 that flushes at 3.5 gallons per flush, or prior to 1994 that flushes at 5.0 gallons per flush, then it might be more tempting to consider a dual-flush conversion kit.

Again, consider the following:

  • You will likely void the toilet manufacturer’s warranty, if you have any warranty left, if you install a conversion kit in your toilet.
  • The design of your toilet most likely requires the full 3.5/5.0 gallons to clear the bowl. Therefore you run the risk of not clearing the bowl if you install the conversion kit.
  • Conversion kits will typically only allow you to flush liquid waste at a reduced-flush rate. Therefore, if you currently have a 3.5 gallon toilet, it will continue to flush solid waste at 3.5 gallons.

Other options for homeowners

Over the years, many handy homeowners have attempted to reduce their toilet’s water consumption by using displacement objects in their toilet tank, such as a brick or a plastic milk jug.

Displacement products may be used with some success if the toilet flushes at a volume of 3.5 or more gallons per flush; less than that and they will not clear the bowl on the first flush.

Another option is the early-closing toilet flapper, a retrofit product that replaces the toilet’s original, fully-buoyant flapper with a reduced buoyancy flapper. The reduced buoyancy closes faster than the standard flapper, reducing the quantity of water that leaves the tank, hence the term “early-closing.” Again, retrofitting can void your warranty and some municipalities do not approve their use because the flush volume is adjustable, making it possible to flush at a rate higher than 1.6 gallons. This mechanism was used on many of the early 1.6-gallon-per-flush toilets, which many of us know were prone to clogging and not clearing the bowl on the first flush.

Commercial applications

If you are considering retrofitting a toilet in a commercial location, you can consider a flushometer valve fixture such as the Sloan Uppercut.

  • The Uppercut conversion product reduces the flush volume for a liquid-only flush by approximately 30%.
  • The user lifts the handle up for liquid waste and pushes down for solid waste.

Having used this type of toilet in airports and other public places, I can say that old habits die hard, and more often than not, I push the handle down even when flushing liquid waste.

If you choose this product, make sure you provide easy-to-read signage that instructs the user on how to properly flush. This product may be eligible for points under LEED Existing Building: Operations & Maintenance certification.

I recommend WaterSense certified toilets and greywater

If you want to reduce water usage with respect to your toilets, you will be best served by replacing 3.5 gallon (or more) per flush models with WaterSense-certified 1.6 gallon per flush or dual-flush models.

Lastly, you could consider models that utilize graywater, such Water Saver Technologies’ Aqus or Caroma’s Profile Smart 305.

  • These units typically require permits and inspection after installation to ensure that the proper flow restrictors have been installed to protect the water supply from contamination.
  • These products have some design limitations, so make sure they will work well in your specific application.

Tagged In: low flow toilet, dual flush toilet

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