How to stop hydronic convection

hot_rod

downstream of the circ with the check valve, both being in the supply side?

I think it would be better to have the flow check on the return side. This would seem to provide a "gravity gate" on both the supply and return.

You also mentioned the temperature drops as you feel the pipe further along. Perhaps little if any flow.

It is possible to have two way flow in a pipe under the right conditions. Hense the flow protection on both S&R to be assured you have put a stop to that nonsence :)

Makes me wonder how many systems out there actually have small ghost flows that go un-noticed by the homeowners. I've seen indirect tanks slowly over-heat do to lack of adequate S&R protection. Just ma nature trying to always achive thermal equalibrium.

hot rod

Dave_4

How to stop hydronic convection

I have radiant heat heated by a Combicore-II. This week, the new heater was installed to replace a corroded 7-year old original Combicore. I asked the plumber about how to prevent the convection that occurs when heat is not heated and he told me that that's just how it is when you have a big tank of water that is always hot.

I have a Grundfos UPS 15-58FRC with a built in check-valve, as well as a Taco 219 flow check connected two feet downstream. With the circulator off for 24 hours, the temp at the flow check is 110* (water temp is 135*). Measuring ten feet away, the temp of the pipe is 80*. Is this normal?
In the summer, I use a ball valve to shut down the loop, but it seems that there should be a way to make this more care free.

Any advice?

Steve

[Deleted User]

thermal traps

Pipe yourself a thermal trap dropping at least 24 inches down and then return back up also put a drain on the bottom of it all thermal migration should and usually stops also insulate the trap and your hot water piping using a fiberglass pipe insulationm with a real wall thickness like 1 inch no homo depo junk and you should be good to go i use them very often and they have yet to let me down peace and good luck clammy

zeke

quote "have a Grundfos UPS 15-58FRC with a built in check-valve, as well as a Taco 219 flow check connected two feet downstream. With the circulator off for 24 hours, the temp at the flow check is 110* (water temp is 135*). Measuring ten feet away, the temp of the pipe is 80*. Is this normal? In the summer, I use a ball valve to shut down the loop, but it seems that there should be a way to make this more care free.

Any advice? "

80 degrees at 10 feet is not thermal convection but is mostly conduction thru the pipes and is normal and should not be a cause for concern since very little heat is lost from this. If it still bothers you, go for the thermal trap recommended or put in a spring loaded check valve in place of your swinging check valve. It should be pointed out ghat the ideal check valve does not prevent thermal convection since it flows in the same direction as the system.

I personally don't think it is worth the expense or the bother to make the change.

Charlie Taylor_2

Thermal Trap not working

This past weekend I installed a thermal trap on my Combicore. The pipe comes out of the hot tapping at the top and then goes down below the cold tapping and then rises up to the heating loop.

Despite the above, the convection is high enough that the room is heating up in this mild weather. The delta on the heating loop is 40*: 130* out and 90* return.

I'm tired of having to manually close a ball valve on warm days.

What now?

Weezbo

turn the appliance off a while.*~/:)

or maybe insulation of the pipe would help....

Mark Hunt_3

Question


Do you have a thermostatic mixing device on the radiant side?

Mark H

hot_rod

I agree

with Zeke, I think you are sensing conduction transfer. If anything a spring checK on the return side would provide 100% check protection for both S&R.

I've seen zone valves used also, but an overkill in my mind.

You might pull the circ to be sure a piece of debris isn't holding the check open. doesn't take much.

hot rod

Steve Garson_2

If it was conduction transfer, it runs 30-feet to the warm tile floor in the bathroom:-)

I'll check if the circulator has debris in the check valve. I surprise that the big heat trap did nothing.

Paul Pollets

Check valves

We always put a spring loaded check valve at the pump outlet and on the return. Ghost flow can be a problem without them.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Charlie Taylor_2

The flow check is down stream of the circulator around a foot or so. What model 3/4-inch spring flow check do you suggest? I'm amazed that the room is being heated with gravity through four radiant loops in the room at the far end of the house.

Charlie Taylor_2

Best spring flow check

Is one better than the other: Bell & Gossett 3/4" Threaded Straight-Angle Flow Control versus
the 3/4" CxC Horizontal (Bronze) Taco Flo-Chek?

Thanks,

Steve

Charlie Taylor_2

Grundfos integral check valve

The thought just occurred to me: if my circulator is pumping away with the intake at the hot side of me water heater, for the check valve to work, wouldn't it need to be mounted in the opposite direction to stop the heat from circulating by convection? Did the installers connect this properly?

hot_rod

hot_rod

This is what's is in that circ

as far as a check device. It is a spring check with a 1/2 psi spring, as I recall. The circ, when running, creates enough pressure difference to pop open that check and allow flow. When the circ is stopped the spring seats the check to stop any thermal induced flow.

If it were reversed as you mentioned the circ would never open the check.

I don't think either valve you mentioned is a spring check? I believe they are weighted style.

I prefer the low spring tension spring checks for absolute closure. Provided they don't have a solder ball, copper chip, or dirt holding them open :0

Watts, Conbraco, Jomar, and most all the valve manufacturers sell low 'pop" spring checks specfically for hydronic use.

hot rod

Glenn Sossin_2

Conduction ?

I agree with Hot Rod and Zeek - sounds primarily like conduction. Has anyone considered or tried splicing a piece of pex, at the heater as a part of the heatrap. It won't conduct heat like the copper and take a big bite out of the conduction component.

Patchogue Phil_32

water

wouldn't the water conduct the heat still thru the pex?

Glenn Sossin_2

Alot less

If we assume this problem is primarily conduction, the water isn't moving.

Trying pick up a piece of 3/4 copper, and then a piece of 3/4 pex. You feel the difference, the copper feels colder - because it conducts heat better. If conduction is a major contributor, all I'm suggesting is, splicing a some pex would reduce that rate because it doesn't conduct heat as well.

I don't have the numbers but, I believe you could compare the specific heat of pex versus copper to get an idea of the conduction relationship between the two mateials.

Patchogue Phil_32

not what I meant :-)

I meant the water INSIDE the pex would conduct heat, even if the water is not moving.

And as you say, no heat loss to the air from the pex so that heat (that might have been lost to the air via the copper section) can also be conducted via the water.

Charlie Taylor_2

The right check valve

I'm looking for the right check valve online. At the Watts site, I couldn't find any spring checks. At Conbraco, they have a few, but they have options on the spring strength to open: 1/2-psi, 5-psi or 10-psi. But the specs state that they are for stopping reverse flow.

I just want to be sure to install the correct devices.

Thanks so much.

Glenn Sossin_2

I was thinking of that too

last night when you posted. Will see what I can find out.

Steve Garson_2

I just bought a spring check valve. This weekend I'll install it and make sure there is no debris in the check valve inside the circulator. I'll post my results. Thanks to all.

EMC PLUMBING

check-trol by B&G

any body ever use these check-trol isolation flanges have had problems with the ifc pumps with unwanted flow have been using flow check valves but was wondering if thses flanges work

zeke

Steve,
ALL check valves allow flow in the direction of the circ pump and stop in the opposite direction. Natural convection, unfortunately occurs in the same direction as the system when the circ pump is off, so an ideal check valve does very little to prevent natural convection.
What we are all telling you is that a spring loaded check valve will need an additional pressure to overcome the spring and will be enough to stop the differential pressure exerted by the thermal flow.
As an example,I determined the thermal pressure on a system where the radiators are 30 feet above the boiler and assuming a supply leg of 140 deg and the return leg of 104 degrees I got a pressure differntial of 0.3 feet of H2O, of about 0.12 psi.These numbers are miniscule and a 1/2 lb spring check should be enough, even if your height is greater than 30 feet and the differential temperature greater than 36 deg as I assumed.

Steve Garson_2

Check Valve in Circulator

This morning I pulled the circulator and clearly saw the problem: an enormous amount of rusty gunk that had collected in the circulator and clogged the check value. Take a look at the attached photos. This circulator is one year old!

The plumber who replaced my Combicore told me that the corrosion was due to the original installer using a three foot piece of iron pipe with no dielectric union to the copper pipe.

The crud explains why the water I drained looked like mud. I removed the circulator, took it apart, and carefully scrubbed off as much crud as I could. Everything works now and there is no longer any convection taking place.

Now the next question: should I flush out the entire system so that any remaining rusty gunk is flushed out, or will the introduction of oxygen in the new water be worse than leaving thinks as is. I want to do whatever is more likely to eliminate future problems. The system has a Spirovent, so there is good air removal.

Opinions experts?

Thanks,

Steve

Steve Garson_2

Check Valve in Circulator

This morning I pulled the circulator and clearly saw the problem: an enormous amount of rusty gunk that had collected in the circulator and clogged the check value. Take a look at the attached photos. This circulator is one year old!

The plumber who replaced my Combicore told me that the corrosion was due to the original installer using a three foot piece of iron pipe with no dielectric union to the copper pipe.

The crud explains why the water I drained looked like mud. I removed the circulator, took it apart, and carefully scrubbed off as much crud as I could. Everything works now and there is no longer any convection taking place.

Now the next question:

Should I flush out the entire system so that any remaining rusty gunk is flushed out, or will the introduction of oxygen in the new water be worse than leaving things as is. You would not believe the color of the water that came out of this circulator when I flushed it.

I want to do whatever is more likely to eliminate future problems. The system has a Spirovent, so there is good air removal.

Opinions experts?

Thanks,

Steve

Weezbo

from what i see,

that is not something that a simple flushing of the system will eliminate.

while it May be a way to reduce flow rates you are likely to have far more remedial work ahead of you than you first conjectured,...

Charlie Taylor_2

Can you elaborate?

Can you elaborate a bit?

Weezbo

at the moment i am on a mad dash after a steam control

and must meet with the electrician to discuss control strategy ,and spin in a RMB and jazz up the two lower zones of a radiant slab... may i do so a bit later when i get home?....

Thanks for the consideration....

the question is a bit rhetorical i am sure...

Charlie Taylor_2

Actually, the question was not rhetorical. Before this Combicore was replaced three or four weeks ago, the plumbing had a 30-inch piece of iron pipe that ran from the radiant hot out to a iron elbow to a copper thread to sweat connector. When this pipe was cut out, it had perhaps a pencil thickness of an opening in it. This was seven years after installation.

When I replaced the Taco circulator four years ago, it had seized over the summer from rust. Two years later, I replaced the circulator again with the same problem. Last year, I replaced the circulator yet again with the Grundfos. But today, I was able to remove it and clean it up pretty well.

Now that there is no iron pipe in the system, my hope is that we can end the corrosion.

This afternoon I decided to thoroughly flush the system. It took around fifteen minutes of constant flow to have clear water come out of the hose. It seems that the rust only collected on the iron parts of the system. All the copper pipes cut during the install were clean on the inside.

Does the fact that there is some remaining minor rust in the circulator mean it will grow again like a cancer? I'm really disappointed by the company that did the original install. I would die if the Onix tubing gets damaged from this and I am forced to install baseboards ...before I die of old age, which hopefully won't be for another forty years or so.

hot_rod

Any non barrier tube used?

I'd guess you have O2 ingress somewhere. Far too much corrosion to be caused by the O2 in the original water fill.

Or you have fresh make up water being added due to a small leak in the system?

Best cure would be to find and limit the O2 ingress.

If not you will need to use, and replenish an O2 scavanger chemical. Not unlike what is used on open type OWF's to stop rusting.

I'd use a good hydronic flush cleaner, then add a hydronic system treatment. One of the main componebts of those products is the O2 scavangers.

It does get used up over time if even small amounts of O2 are getting in.

Same thing happens with glycol systems when the scavangers get used up.

! doubt the steel to copper connection caused this and would not use dielectric unions in any closed loop hydronic system. They are just not needed. Corrosion and rust will not occur in an O2 free condition.

hot rod

Charlie Taylor_2

Hot Rod:

Thanks for the information. All the tubing is Onix which has an oxygen barrier, unless, of course, the tubing had a manufacturing defect. I guess we'll never know. Besides that, everything is now copper.

I suppose I should contact Watts Radiant to confirm which oxygen scavengers are acceptable.

Thanks for your help.

Steve

Charlie Taylor_2

Can you suggest a cleaner and water treatment. I looked at the Rhomer products but I can't believe the price. I don't need a whole gallon based on the concentrations needed.

Weezbo

well, i am back:(

it was a forced change of plans as it were.

ok so the question in question, which was a certainty , is now answered by my return.

first off the bat is get right information in order to "steer' ones thinking to the second point of intel the cause, to focus on its Source.

Only in Acupuncture can one fight all the symptoms and syndromes ,correct all of them and that rectify the source, when the specific Source still remaining elusive to identification. *~/:),

what is the source of water into the appliance?

have you done an examination of the headers of the tubing?

have you or anyone else in the process taken the time to re-pressurise the 'system' side of the heating and check it with ultra sound? the boiler side to 30 psi? and leave it alone for a day to double check the readings?

anyone do a water sample test on the water feeding the system?

a water test of the water within the boiler?

are or were there any observable "Leaks" around the boiler or header connections?

does any of the tubing go "Underground" anywhere within the supply and return piping to the headers?

are you adverse to using a plate exchanger with strainers on both sides of it with an expansion tank on the system side, with a known quality and type of solution?

when you flushed the system side,...what was your Flow rate per min ? how about the boiler side?

with some answers ..whatever they may be i think we would have something slightly more empirical to "go on' ...
the cause is what we will most likely be able to determine...that does Not (spelled out real clear like) N O T preclude more than one cause...




.

Charlie Taylor_2

Here you go:

what is the source of water into the appliance?
>City water: Newton, MA. Not hard at all.

have you done an examination of the headers of the tubing?
>Good question. Its behind a panel in my garage, so no. I will look tomorrow.

have you or anyone else in the process taken the time to re-pressurise the 'system' side of the heating and check it with ultra sound? the boiler side to 30 psi? and leave it alone for a day to double check the readings?
>Another good suggestion. I have a pressure gauge on the line at 20psi. I haven't tested it to 30psi. It is very possible that air was introduced by the failure of the Combicore which may have interconnected the potable with the hydronic, but who knows. As far as checking with ultrasound, no one has done that.

anyone do a water sample test on the water feeding the system?
No.

a water test of the water within the boiler?
No. Again, this was just replaced less than a month ago.

are or were there any observable "Leaks" around the boiler or header connections?
There was a minor amount of rust underneath the PRV that is above the water heater.

does any of the tubing go "Underground" anywhere within the supply and return piping to the headers?
>None

are you adverse to using a plate exchanger with strainers on both sides of it with an expansion tank on the system side, with a known quality and type of solution?
>I'm open to anything

when you flushed the system side,...what was your Flow rate per min ? how about the boiler side?
>The flow rate was probably around 3GPM. I didn't open the regulator all the way, perhaps I should have. When you refer to the system side and the boiler side: This is a Combicore, so the potable hot water tank is the "boiler" and the PEX coil inside the tank is the heat exchanger for the radiant system.

with some answers ..whatever they may be i think we would have something slightly more empirical to "go on' ... the cause is what we will most likely be able to determine...that does Not N O T preclude more than one cause...

Thanks SO MUCH for your time and attention.

As as aside: my convection started again, despite my addition of another spring check valve, so obviously some more crud must have floated into the valve. This is frustrating.

Steve

.

Charlie Taylor_2

Will the expansion tank support pressurizing to 30psi?

Bruce Stevens

Yes the expansion

tank is rated to take 30PSI, has to be to be on a boiler

hot_rod

Good question about the O2

source. I see and hear about that problem from time to time??

I'd be glad to send you a small quanity of Rhomar. Do you know the system capacity? I suspect a pint or so may do it.

hot rod

Weezbo

yes to the expansion tank question...

and if it is truly a stainless steel expansion tank there is every likelihood that it may be charged and tested to 100 psi.

is it an ST-12, or an x-trol tank?

you would need to check the manufacturers literature to determine if i am making that number up or not though ...as i am aware of more than one change to various products having made to conform to lower standards than we once enjoyed in the U.S.A.

Weezbo

i just came away from some pinner leak next door ...

brand new shiny chrome valve..so, if a new valve can leak surely there should be no great expectations of older valves

however many of the older valves held water , stopped the flow when you turned them off, and basically let the water through them when they were opened Whole Notha Laval these days
*~/:)

'honestly there are people who probably have full time work rebuilding failed valves, stems ,seals packing, ... on some jobs ...buh i digress...

i think that when you look into some of these other minor technicalities you may find that it would be to your advantage to pay a couple $ to put caps on some purge valves, boiler drains, tighten to snug some Bonnets on valves...maybe even, re tweak the headers on the supply side of the Onix tubing... if there appears to have some visible sign of leaking ....then, You have to consider the incoming water , it may need to be filtrated prior to it running into the system ...If you take a look at Brad Whites boiler install ,you will see another appendage to the boiler. That gizmo dials in a bunch of minor technicalities bailing around a boiler system...sorry , eliminates various substances from within the stream of the fluid.... there is one that the system 2000 is "Up On " these days ...that with a strainer could be a way to help. It depends though, on the water or fluid test analysis....

the pressure test should work by valving off the heder...well enough. the prv should have no difficulty at 28 P.S.I.




i would like to know if you have opened the strainer on the bottom of the pressure feed valve to the boiler (with it properly valved off) just to see if there are any signs of mineral build ups ?....take a white bucket, valve off both sides of the regulator that lets water into the boiler. Remove the strainer cap at the bottom of the regulator, shoot some water thru the supply side to it,...let it blast into the bucket, then with it valved off on the supply, try the same thing by opening the boiler side valve .....even though you said you have it valved off and seldom use its auto feed ability,...sometimes that is a point of enlightenment...


the other thing is is this some boilers are piped 'Different' than others , what i mean by that is they have air relief valves or air eliminators that allow the change of the atmosphere within the boilers ,..meaning they can operate as a two sided sword that cuts both ways. one way they eliminate air, the other way (depending on the way it is piped and a few other minor technicalities)they take on air to fill a vacuum...

i type slow.:( i probably timed out...let me post this and go from there...

Charlie Taylor_2

More on my radiant problems

Weezbo:

Thanks again for your suggestions. It's frustrating that I can't stop my heat without turning a ball valve:)

I will check the strainer on the regulator, but your notes made me wonder:

1. When the system was replaced six weeks ago, the expansion tank was non-functional and full of water.

2. There is an air vent not far from the expansion tank. Is it possible that it is letting air in, instead of just letting it out?

3. I pressurized the system and there was no drop in pressure after 24 hours.

A appreciate your offer for some Rhomer product. As a practical matter, I would hate to impose on you since it would be a real challenge to find a suitable container that you could ship, unless you've done this before.

I am estimating the total system volume at around 10 gallons.

If it weren't for this site, I would have just been dealing with another circulator in a year or two and wonder why.

Thanks for your help. I'm going to check the strainer now.

Steve