RO/DI hooked up to cold AND hot supply

[Myka]

Who has their RO/DI plumbed in so that it's getting a bit of hot water mixing in with the cold? How are you doing it?

Most people just plumb the RO/DI into the cold water line, but I don't want sweaty lines dripping on my finished floors. I don't want to insulate the RO lines to prevent the sweating because I also want to take advantage of the higher product ratio from using slightly warmer water.

I have always just had the RO hooked up to a sink tap and just turned the hot water tap on a bit. Now I moved the system into the laundry room (no sink) and have to figure out how to plumb it into the washing machine hookups. The cold water line is already split for the steam washer and steam dryer, and the hot line is just going into the washer. Can I just split the hot water line and (and the cold water line again) just use butterfly valves to control the hot/cold flow to the RO?

I have a little voice in the back of my mind from my construction days telling me that hot water lines need to have open ends and can't be pressurized. The voice says the pressure from the cold water might back flow into the hot water line and pressurize the hot water tank, but isn't the hot water tank already pressurized? I think there might even be a check valve on the product side of the hot water tank maybe?? Maybe I'm overthinking it and the little voice needs to shut up...

[WarDog]

Your hot and cold are going to be equal pressure all throughout the house, within a psi, as it's all being fed through the prv coming off the street supply at the point of entry where the shut off is.

[Ryanerickson]

In 4th year plumbing they taught us that ro units should be hooked up directly to hot water supply apperntly it's more efficient I've always used cold

[Myka]

Originally Posted by Ryanerickson

In 4th year plumbing they taught us that ro units should be hooked up directly to hot water supply apperntly it's more efficient I've always used cold

Interesting. Filmtec website says maximum operating temperature is 45C (113F), and looking at a bunch of other brands it looks like 42-45C is pretty standard. Our hot water is a lot hotter than 45C. My understanding is that high temperatures will melt TFC membranes.

I certainly wouldn't want to pay the electric charge to heat all that water either. I just want a trickle of hot water...

[shiftline]

Doesn't hot water kill the RO membranes faster?

[Ryanerickson]

I would think so lots of hot water tanks have rust inside,I thought the idea was odd last few days of the coarse the teacher gave us a bunch of photocopied paper work. One was about reverse osmosis. Mindy the proper way to do this is with a mixing valve you could get one from a plumbing wholesaler. They are commonly used on faucets in public washrooms that are touch less operation.

[spit.fire]

Originally Posted by shiftline

Doesn't hot water kill the RO membranes faster?

Yup

[hillegom]

If the pressures in house plumbing, hot and cold, are equal, why not put a john guest 1/4" ball valve in the hot water line and open it a smidgen. You would then use two one way check valves so that the hot and cold doesn't mix.

Just as an aside, hot water tanks have sacrificial zinc anodes in them.
they corrode before the steel does. Your RO membrane would have to take on the additional job of removing zinc. But I do not think that there would be very much of that in the water. The anodes last at least 5 years, the length of time most hot water tanks are warranted for.

[The Codfather]

Originally Posted by spit.fire

Yup

Agreed, hot water will damage the menbrane. As mentioned a mixing valve is the best way to blend the water, shoot for 20-21C for best performance.

[Myka]

Originally Posted by The Codfather

As mentioned a mixing valve is the best way to blend the water, shoot for 20-21C for best performance.

I never heard of one before this thread. Now there is an answer! I'm glad it's this simple. I even found a SharkBite one so I can install it myself. Thanks guys!