Heat Traps, Hydronic Heat, and Optimal Return Line Placement

[AFinePilsner1]

Hi gang. I'm proactively replacing my 21 year old Lochinvar (giddy up). I have attached an image of my current hot water and hydronic floor heat setup. Basically, the original installer mixed a top discharge with a side return instead of doing both at the top or both on the side. It really is an elegant system though and has worked flawlessly and cheaply all these years. I know, right!

I am curious about how the standard heat trap nipples on the new water heater will work with my closed loop hydronic heating system. I have lots of trade skills, but managing the thermodynamic properties of water is not one of them. Here are my options:

1. I could install the new water heater the exact same way. My fear is that the heat trap on the top cold water inlet might function like a partial check valve though. I wonder if the cold water heat trap on the inlet will cause some strange back pressure build up as the new cold water competes with the returning warm water.

2. I could make the warm water return to the top on the cold water side just after the inlet ball valve. I hope that someone can confirm though that putting the return line there will not cause a back flow problem. [Please note that the manufacturer install image does NOT show a check valve and expansion tank at that connection. This topic was debated on a different discussion board https://www.plbg.com/forum/read.php?1,294601.]

3. I could remove those heat traps from both inlet nipples and run the new water heater just like the last one. They just pop out. I am sure there is heat loss, but the system seems to work well now.

So, what would you guys do if this were your house?

PS- While I have your attention, that ball valve on the automatic system refill on the closed loop hyrdonic section (see image) should probably be off and turned on once a year before heating season or if I ever notice a pressure drop. However, please notice that there is little bit of pipe after it and before the backflow preventer. In my mind, water can trap and stagnate there all year and then enter my water heater when I turn it on to top off, so I had been leaving it on. Shouldn't that technically be an all-in-one Watts combo there or something else? I think the original plumber improvised. Please note: There is a heat exchanger to separate the systems.

 

[Fitter30]

I wouldn't have piped the system like you have but if it works pipe the new heater like the old the heat nipples won't be a problem. The wh dip tube on cold is attached to the dip tube. That line from back flow to ex tank is putting 50-60lbs of water pressure on the floor and heat exchanger. Water between backflow and ex tank is probably stagnate. What type of glycol are you using? Automotive or boiler type? If there was a small leak in the floor heat it could be possible that one wouldn't see it dilute the antifreeze then there wouldn't be any protection. Instead of having make-up on all the time. Floor side a male hose fitting at back flow and at shut off use a wash machine hose in between. Need to add water crack water valve bleed air out or the hose before opening valve further.

 

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[AFinePilsner1]

Thanks! I appreciate your insight about those heat trap nipples. I also appreciate the tip about adding that hose fitting. I assumed that I had Propylene Glycol in the system because it was clear, but I could be wrong. For all I know, this thing could have been replacing water in the closed loop for a couple years before I bought the house. I shut off that refill valve and will watch the pressure. Assuming nothing drops, I will flush the system in the spring and add that fitting.

 

[John Gayewski]

Heat trap nipples aren't a check valve they only stop ghost flow they can't stop a pump and you can actually cut the little flapper if you want.

You shouldn't tie your hydronic heat in with your domestic hot water. It's a bacteria petri dish. They need seperated by a heat exchanger. I would be willing to bet it's not legal even in Michigan.

 

[AFinePilsner1]

Heat trap nipples aren't a check valve they only stop ghost flow they can't stop a pump and you can actually cut the little flapper if you want.

You shouldn't tie your hydronic heat in with your domestic hot water. It's a bacteria petri dish. They need seperated by a heat exchanger. I would be willing to bet it's not legal even in Michigan.

Thanks. I suspected that the flap traps were less aggressive but wanted to be sure since I don't regularly deal with hydronic heat systems. The fact that the old system was plumbed non-standard to begin with also caused me concern.

Right now, I'm leaning toward just returning the warm water to the cold inlet like the manufacturer recommends. I guess the worst case scenario is that a fixture sucks some warm water and I have to insert a check valve and expansion tank.

So that I clearly understand best containment practices: The hyrdonic system is on a closed loop that runs through a heat exchanger. However, there is a bridge with a backflow preventer used for topping off the system with water. Are you saying that this connection feature probably shouldn't be there at all? I have no problem capping it off and filling manually if that is the best practice.

 

[Breplum]

You need to use a heat exchanger.

 

[AFinePilsner1]

You need to use a heat exchanger.

Agreed. There is a heat exchanger to create a closed loop heat system. However, the original plumber engineered an auto refill, which I suspect, creates a stagnant water spot even if working correctly.

I think that such engineering can be done better, but I’m not sure if having an auto refill is current best practice.

 

[John Gayewski]

Your drawing is showing the hot water for the house and the hot water for heating coming from the same pipe. Are you saying your drawing is wrong?

 

[AFinePilsner1]

The red loop is potable water that flows through a plate heat exchanger in one direction. The heat exchanger is in about the middle of my drawing. The purple loop is a closed loop heating system filled with antifreeze that flows through the same heat exchanger from the opposite direction. The fluids are isolated and do not come in contact with one another. Up until that point, everything is normal as far as I can tell.

However, and here is where my question comes from, the original plumber also added a water makeup system that taps the potable water to make up any lost fluid in the heating loop. This is why I have drawn the red line going into the back flow preventer and a purple line going out. I just scribbled on my image to make this more clear for everyone. I am certainly not an artist.

Code may allow this (as it does for boilers, various sprinklers, etc.), but I'm not sure what current best practice is and what pros do in their own homes. For example, I bet most sparkies side wire receptacles at home, and the floor guys undercut their door jambs. Perhaps no refill at all is the way to go in this case. I always appreciate any advice and learning.

 

[John Gayewski]

Oh, if that was leveled heart exchanger I missed it it looks like how they draw an emitter normally.

Makeup water with a backflow is fine, he did it right.

 

[AFinePilsner1]

It probably is an emitter image. Lol. I just picked whatever clip art I could find that looked like the parts I needed. If I drew them it would have been comical. Thanks for responding.