RO/DI hooked up to cold AND hot supply
 

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... :neutral:

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.

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

Doesn't hot water kill the RO membranes faster?

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... :D

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.

Yup

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.

That sounds like a good idea...I'll look into these and see if I can incorporate it.

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.

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! :)

There's a trade off to the better production ratio eh? IMO, save yourself the hassle. Not only are you using more energy for a bit or warm water, but the rejection rate with warmer water is worse, so you'll burn thru DI media faster. Personal experience with my unit in winter vs summer - summer RO TDS @ about 14-16 degrees C incoming water temp = 1. Winter RO TDS with incoming water @ about 8 degrees C = 0. I can live with a slightly lower production rate thank you very much. Incoming TDS for the most part is in the 160 to 170 range in my humble abode. That's Kalamalka Lake water. On the rare occasion they switch us to Duteau Creek source, TDS drops to 50!

The temp of the water here entering the house is right around 4C, so it does improve production quite a bit by increasing the temp. I have a zero waste, so i have no reject water, so i guess pending on your situation and your water quality to start with, it does make a difference.

M, do you have a booster pump? Or do you run on line pressure? I guess depending on what your requirments are, maybe youd be farther ahead by adding a booster pump instead of blending your water for better production.
If you go the cheap route on a blended control, it is not very accurate, also depending how you distribution piping is done, you may find that there is a large pressure difference between the hot and cold. There are a few factors to consider, id boost before i blend. I have access to the equipment through work, thats why i went cadillac on my system. Just my 2cents.

My tap is at 65 psi and it's a 150 gpd membrane. I had a booster pump but it only improved production from 1:1.7 to 1:1.6 so I didn't use it. For me the biggest difference in production is incoming temperature. Cold tap water this time of year is 4-6C and in summer it is 8-12C. If I boost it up to 20C then my production almost doubles.

I'm not concerned too much about DI as it hasn't been a problem -even dealing with ammonia in the RO water from chloramines I just replace the DI when I replace the prefilters...it's pretty burned up by then.

My tap water is 180-220 and has chloramines so I run two carbon filters. My membrane is 4 years old or something and is running at 8 ppm last time I checked. I flush it lots. It's holding it's own. :)