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Old 03-05-2021, 02:50 PM   #1
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On Demand Hot Water Mod - Your Thoughts?

We always had a conventional, 6 gal water heater. Our new to us 2018 Thor Quantum has the Girard tankless. I understand how it works and I have the same problems that most users have - if you stop the hot water flow and then restart it 10 to 20 seconds later, you will get a short period of hot, then a short period of cold every time before it evens out again. This seems unavoidable because the water stops IN the heater, gets hot over a few seconds, you turn it back on and that hotter water hits you, and right behind it is the cold water that passed thru the heater BEFORE it turned back on.

I want to keep this heater but I want to minimize this effect to a greater extent than I'm able to by just operating it correctly - cuz that's just not enough, especially if your trying to wash dishes in the sink and preserve water. I'm thinking of doing two things:

1. Install an accumulator tank to even out the pressure. I found a one liter capacity accumulator, figuring the 1 gallon was just too big but the 1/2 or 3/4 liter ones would be less effective. My inclination is to put that right after - just downstream of - the water pump. I'm sure this will help a bit, as it has for others.

2. Install another tank, not an accumulator with a bladder, but just a holding tank of about 1 liter capacity, with TWO openings, somewhere in the hot water line. This tank would simply get filled on one end and go out the other, with no effect on the pressure. My thought is that the hot blast and the cold blast of water from the heater would MIX to some extent in this tank, thus decreasing the "swing" in water temp that ultimately made its way to an outlet. The bigger the tank and the better the mix, the less the variation in temperature. Obviously, the smallest possible tank is preferable.

I can't find any such holding tank smaller than 1 gallon, which seems too big to bother with - might as well get a 6 gallon replacement heater.

So... I'm thinking of using 2" PVC, maybe 12-15" long, capping it at both ends, and installing a suitable connector on each end (on top of one side, bottom of the other to promote mixing) so I can place it inline in the hot water line.

I could install it right after the heater, so it feeds to all the outlets, or I might install it right before the kitchen sink because that's where I have the most room and that's where I have the biggest issue with temperature fluctuation.

Other than "managing" the inherent quirks of this system by operating it "correctly", I haven't found any other mods suggested by anyone to minimize this issue with on demand hot water systems.

Anybody have any thoughts? Anyone thought of doing this?

Thanks... Joe


PS: I impressed my own self when I thought of this because of it's simplicity. I'm thinking I might soon find out why that was premature...
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Old 03-05-2021, 09:03 PM   #2
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If you can run a line back to the fresh water tank from the shower, this device could work.

You set the water temp and leave it running. When you switch the valve it send the water back to the tank. No waste.

https://aquaviewinc.com/rv/

Don't have one yet but looks promising.
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Old 03-05-2021, 09:35 PM   #3
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Originally Posted by twinboat View Post
If you can run a line back to the fresh water tank from the shower, this device could work.

You set the water temp and leave it running. When you switch the valve it send the water back to the tank. No waste.

https://aquaviewinc.com/rv/

Don't have one yet but looks promising.
TB, that is nuts. How the heck did you find that:-)
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Old 03-06-2021, 02:28 AM   #4
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Wasn't me.

Another IRV2 user posted about it a few months back, I remembered it, I just had to find devices name.
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Old 03-06-2021, 08:02 AM   #5
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Yeah, the showermiser is a GREAT idea, and I'd do that except that running a line back to the tank seems real difficult in my rig, so I'm trying to avoid that. Also, it would only work for the shower, if installed there, not the other outlets, like the kitchen sink.

Anyway, I'm hoping that by mixing the hot and cold blast in the PVC "holding tank" right after the hot water heater I can make the temp at the outlets a little less variable and more tolerable. The question is whether it's gonna be effective enough to warrant the effort.

Thanks for the comments!!

Joe
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Old 03-07-2021, 05:14 AM   #6
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Originally Posted by JPZLAW View Post
Yeah, the showermiser is a GREAT idea, and I'd do that except that running a line back to the tank seems real difficult in my rig, so I'm trying to avoid that. Also, it would only work for the shower, if installed there, not the other outlets, like the kitchen sink.

Anyway, I'm hoping that by mixing the hot and cold blast in the PVC "holding tank" right after the hot water heater I can make the temp at the outlets a little less variable and more tolerable. The question is whether it's gonna be effective enough to warrant the effort.

Thanks for the comments!!

Joe
If you look at the Aqua View website you will see that they also have kits for the kitchen sink. It is basically a diverter valve that will flush mount in a counter top. Continuous circulation of the output of a water heater is not a new ideal and I know at least two people who have homes where the water is circulated back to the tank so that when you turn on the water it is already hot. This is certainly not energy efficient but may not be the energy hog you expect just like your air conditioner will take much longer to cool down a room from 100 degrees if you only turn it on when you are home.

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Old 03-07-2021, 05:35 AM   #7
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Don't know if this will work. working with cosmetics we used motionless mixers
It creates a lot of turbulence as the liquid goes through the pipe.
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Old 03-07-2021, 05:45 AM   #8
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We have a ten gallon tank but this mod might work for you too.

On another thread someone posted a modification that I absolutely love as does the wife.

A mixer valve was installed in the hot water line. The valve mixes cold and hot and sends out a constant temperature no matter who flushes or turn on a faucet.

The mixer valve is brass and around $80. It does not take up much space.

In addition I changed the t-stat on the water heater to a higher temp one. So more hot water to start and then mixed down gives longer and steady showers.

The water temp can be adjusted so it never gets too hot.

If interested I will find the thread and post the link.

In a past rv having the same problem of either a hot burst or a cold burst, depending on the rv we had, a simple ball check valve was installed in one line or the other just behind the shower mixer valve but could be installed in a lot of places.

I do not understand the physics of how water can back up a line when they have the same water inlet pressure but it seems to happen. This issue happened when using the on/off valve on the shower head.
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