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Author Topic: Water heating problem  (Read 2524 times)

Mike Watkins

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Water heating problem
« on: October 29, 2017, 03:22:42 PM »

A G200 feeds my house and my garage - separate buildings.  Above the garage is a guest apartment.  There's a 40 gal. electric water heater in the garage (primarily for the apartment but also for my shop in the garage) that's hooked in to the G200 lines and has a heat exchanger sitting on top of it that is connected in to the cold feed and is as hot as hell!
Yet, the water coming out of the hot tap is cold.  If I run the hot tap for 5-10 minutes it MAY just reach tepid.

In the main house, everything works well.  The garage is exactly the same configuration.

I imagine the problem is insufficient, continual hot water useage out in the garage to allow the hot water to permeate throughout the water heater tank so while very hot water is coming in to the bottom of the heater tank it's just going cold by the time it gets to the top and feeds out the hot water tap.

Other than shortening the tank's cold feed to deliver hot water to the top of the tank does anyone have any neat ideas on how to fix this?
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hondaracer2oo4

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Re: Water heating problem
« Reply #1 on: October 29, 2017, 04:10:59 PM »

Does it have a tempering valve? They do fail. Have you tries running the water heater with electricity and see if you get hot water? When you pre heat the water with the flat plate it ussually takes a couple mins to get the hot water to te tap.
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Mike Watkins

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Re: Water heating problem
« Reply #2 on: October 29, 2017, 06:42:40 PM »

Thx hondaracer2oo4.
The water heater works fine as an electric heater.  When we have guests in the apartment, I simply flip the breaker on and within an hour or two they have hot water. 
Not sure what you mean by a "tempering valve", exactly.  Is that the same as the "T&P" valve on the parts explosion I checked?
Don't know what it's function is precisley.
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hondaracer2oo4

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Re: Water heating problem
« Reply #3 on: October 29, 2017, 07:32:18 PM »

No a tempering valve is placed on the outlet side of the water heater to mix the outgoing water to safe temp. I assume this is a flat plate heat exchanger, how  many plates and what are the dimensions? Any way to measure the temp leaving the hx before it enters the tank?
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RSI

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Re: Water heating problem
« Reply #4 on: October 29, 2017, 08:11:43 PM »

If it is just not being used enough to keep the tank hot then you could just add a small recirc pump between the hot and cold lines above the plate.
If you do have a mixing valve then you will need to connect the pump before the mixing valve.


If you don't want to do the pump, you could switch it over to a sidearm configuration instead. Or another option would be to move it to the hot side and use it as on demand instead.

If you don't already have a mixing valve, you would have to have one if you do the sidearm or plate moved to hot line.
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E Yoder

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Re: Water heating problem
« Reply #5 on: October 30, 2017, 02:21:00 AM »

As was mentioned, sounds like there's not enough use through that water heater to replenish hot water off the heat exchanger. But- that means leaving the electric on won't cost much at all. And it'll begin working when guests are using hot water and pull fresh hot water in.
Or the recirc pump or sidearm would work as was suggested.
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Mike Watkins

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Re: Water heating problem
« Reply #6 on: October 31, 2017, 05:22:59 PM »

Managed to lock myself out of this forum by updating my email address but, thanks to Marty Lappin, I'm back in now.

Thank you for some good suggestions - some of which (sidearm, tempering valve, to name just 2) I had to research to find out what they do.

Eldon Yoder's suggestion is the simplest, of course, but I don't really follow why it wouldn't cost much?  If I only use the hot water in the workshop - maybe briefly, twice a day - aren't the heating elements going to be working almost as hard to maintain temperature, especially when my HX is ineffective in dormant demand?

What I did discover, researching these suggestions, is that my installation takes no account of the concept of a "thermal block". Across my entire installation, the plate HXs seem plumbed to create just that!  In the garage, for example, the plate HX sits on top of the water heater with its HW system exit rising 18" before dropping 22" into the cold intake of the heater. The 18" riser is HOT but the drop pipe is COLD - classic thermal block.  Hot water will rise but not sink. The same is true in the main house where the hw exit rises 4 ft. before dropping 10" into the cold intake but there demand is sufficient to keep it flowing and so, while not optimal, it still works.

In both cases, it is only continual demand (or the electric elements) that will keep the water hot since the there is little to no convection caused by the plate HXs.  There is a notion I came across of "thermal pressure syphon" that could create a convection process with the plate HXs but the way they are plumbed right now apparently inhibits that.

All in all, from what I have read and You-tubed, it seems a sidearm is the most logical and efficient way to optimize the heat convection without either power or continual demand- and, for low use installs, perhaps the only sensible approach.  What do you guys think?

If so, any recommendations on a sidearm? Garage HW heater is older (2,000-ish) and has no side ports so would need to use drain and pressure relief valves about 40" apart.

I do not, it turns out, have a mixing valve anywhere in the entire system.  Our water is scalding hot - too hot to hold my hands under - but my wife likes it that way! Maybe she's really from Mars, after all?
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E Yoder

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Re: Water heating problem
« Reply #7 on: November 01, 2017, 03:48:42 AM »

What I meant by not costing much is maintaining temp uses a lot less electricity than heating up water from 55℉.

To convect off of a flat plate you would need a return pipe also to create enough flow to amount to anything. That's how a sidearm works. A flat plate lower than the water heater would get the piping warm but it's not going to thermo siphon any volume of water in and out one pipe. I think I'm understanding correctly?
In the case of your garage/guest room the sidearm option probably would be best. I haven't used them so someone else can better describe the details of installing one.
Another option would be to use two tees and valves to bypass the water heater to pull straight off the flat plate during the heating season. Then you could shut off the water heater electric. But it will be very hot water.
My 2¢. I'd like to hear more ideas.
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shepherd boy

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Re: Water heating problem
« Reply #8 on: November 01, 2017, 04:44:13 AM »

  If you pull directly off the flat plate through a mixing valve (tempering valve) bypassing the water heater, you will have an on demand water heater and nothing will have to stay hot. Add a on demand water heater to it and do away with the standard water heater may be your best option for that situation.
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Mike Watkins

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Re: Water heating problem
« Reply #9 on: November 01, 2017, 04:46:31 PM »

Decided to following E Yoder's suggestion and just turn on the power to the heater for now but monitor power consumption for a while.  I am pretty convinced, however, by what you guys have told me and what I have read, that a sidearm would be the most elegant solution in this particular scenario. 

There was one You Tube I saw that suggested if you plumbed it right, a plate HX could create a convection system because the pressure of the water heating up in the HX is greater than the water cooling down in the tank - they called it "thermal pressure syphon" - thus forcing hot water into the tank creating a convection effect.  Certainly not much of that going on at my place :(

I turn my wood furnace off in the spring so I am comfortable for now leaving the traditional heater in place but, if ever I should find a little spare cash, I shall look into the by-pass and demand heater idea.

Thanks a lot for all your input and great suggestions. Most enlightening. Great learning experience for me.
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RSI

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Re: Water heating problem
« Reply #10 on: November 01, 2017, 05:41:29 PM »

If it is just the tank cooling down, the electric usage to keep the tank hot would take a lot of years to pay off the cost of a sidearm.
If it cools off very fast you could put a thermal blanket kit on it to slow down heat loss.
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