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Old 02-12-2009, 11:30 AM   #1
KGP
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Hydronic Radiant Floor Heat


Ok, I am in the middle of redoing a bathroom (2nd floor of house). While the floor was out I decided to go and purchase a spool of oxygen barrier pex to run a radiant floor heat to replace an existing radiator to gain some space and update the overall room.. Installing the actual plumbing is complete and took all of 20 minutes... bleeding it has consumed 2 days and I am still unsuccessful.

I dont know what was going through my head when installing a 70ft airpocket, but I sealed the system off and never throught of bleeding/purging it. I woke up the next morning to see how the room felt and unsurprisingly the lines were cold. I cut the line realizing I never bled it and installed a T with a bleeder valve (from a radiator) into a new closet next to the return pipe that the pex is connecting to. This line runs directly down to the basement and T's into the rest of the house's radiator returns, so my bleeder is on the return side.

While installing the T, I tried to let the pressure behind the air push the water in the system to the retun side before clamping the T for the bleeder. I "thought" I did so successfully, but there must have been a bunch of air behind the water that started coming out.

I guess the basic question is... what the heck is the best way of bleeding this out?

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Old 02-12-2009, 02:13 PM   #2
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Hydronic Radiant Floor Heat


It sounds like you removed a cast iron rad, that shared the supply and return lines of a cast iron rad on the second floor.

Lot of people have done that, and found out it doesnt work.

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Old 02-12-2009, 02:56 PM   #3
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Hydronic Radiant Floor Heat


If you can get to eather the supply pipe or return pipe and install a valve on the boiler side of the loop you are trying to bleed. Then install a garden hose drain valve next to the shut off valve this goes on the side closer to the loop. You can then close the valve hook a hose up to the drain and the water flow wich can now only flow through the loop and will force the air out of your loop. Now that this is done we dont know if your pump will curculate through the restrictive tubing your system design and pump were designed for radiators not radiant and will most likly not be the perfict tempature eather.
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Old 02-12-2009, 02:59 PM   #4
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Hydronic Radiant Floor Heat


Quote:
Originally Posted by beenthere View Post
It sounds like you removed a cast iron rad, that shared the supply and return lines of a cast iron rad on the second floor.

Lot of people have done that, and found out it doesnt work.
it worked when it was a radiator, now it is hydronic pex line. I find it hard to believe that it "wont work" at all... The radiator that was removed was on the second floor. It was removed and replaced with the pex completing the loop that the radiator made before. It is not sharing a supply or return line any more than the radiator it is replacing (that pumped a ton of heat into the room) did.
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Old 02-12-2009, 03:04 PM   #5
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Hydronic Radiant Floor Heat


Quote:
Originally Posted by JohnH1 View Post
If you can get to eather the supply pipe or return pipe and install a valve on the boiler side of the loop you are trying to bleed. Then install a garden hose drain valve next to the shut off valve this goes on the side closer to the loop. You can then close the valve hook a hose up to the drain and the water flow wich can now only flow through the loop and will force the air out of your loop. Now that this is done we dont know if your pump will curculate through the restrictive tubing your system design and pump were designed for radiators not radiant and will most likly not be the perfict tempature eather.

Thanks, I will try this. I am kinda tired right now and will do some more work on it tonight. I did take a look at the expansion tank to the system and notice that it is now almost solid sounding where I know last season (last time i looked at it) was hallow sounding ( not filled). I will try to drain that as well.
I figured the circulator pump would need to be changed, even if just for that one zone. current ssytem is all one zone for both floors. I was planning to change that out, espically since I will be changing the entire first floor to radiant floor heat.

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Old 02-12-2009, 03:09 PM   #6
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Hydronic Radiant Floor Heat


The pex tubing, is far more restrictive to flow then the rad was.
So you added head pressure to the system. And the circ is not able to over come it.

Common problem.
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Old 02-12-2009, 08:28 PM   #7
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Hydronic Radiant Floor Heat


sounds right and wrong. I can see it now flowing, or working as efficient as it would with the proper sized circ, but why would it not work at all?

Lets take the example of running 2 hoses. One a fire hose, the other a garden hose. Both being 100ft and run at the same pressure. One would tend to think that the garden hose would "fill" at a quicker rate than the fire hose due to the volume of water.
With removing a radiator that was 24in long (I forget the height, but a standard size height) it does contain a good amount of water volume. This radiator was fed with a 3/4 in pipe. The new pex heat is all 1/2in from the original connection still fed with 3/4in feed and return and has a run of about 60ft. I dont know the calculation of how much water that equates to, or how many gallons of water the radiator held, but I cant imagine they are that far off from each other to leave the pump 100% "cant do the job AT ALL".
The supply line in the basement is hot the closer you get to the main supply and cools the further away you get from the main, which makes sense because there is no flow due to the air pocket that was created by installing the pex.

If the comment was that it wouldnt be as efficient as it can be if the circ pump was correct I would understand, but dont see how a simple "common problem" or "it doesnt work" answer is in fact true.

Now I have drifted away from the original question of the best way to purge the system, to arguing why this "wont work", or in my head, will work once the proper pump is in place or it is zoned separately.
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Old 02-12-2009, 09:38 PM   #8
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Hydronic Radiant Floor Heat


Radiant floor heat is designed to run much lower water tempature. Your radiators are probly running 150 to 160 deg. to hot to heat a floor. Not only is the restriction more on a radiant system higher the gpm is different also. It may work somewhat but since it is not a properly design zone you may not get what you want. If you change the pump to handel the radiant it can now change the flow through the rest of your system and goof that up. Unless you zone out the radiant on a seperate loop with a mixing valve. I would leave the pump as is and see what happens 1st.
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Old 02-12-2009, 11:44 PM   #9
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Hydronic Radiant Floor Heat


Your annology is the wrong type.

The hoses would have a pressure behind them that can push water to where it is not.

A circulator can only move water if the water is already there.

Next, circulators only create a pressure differencial. They do NOT pump water, they are NOT pumps.

The radiator had large openigs in it compared to the pex. So it had very little restriction to water flow.
The pex is very restrictive compared to that rad.
So the water that would have gone to the rad that was in the bathroom, is now flowing through the rad on the same line instead, because it is less restrictive, and easier then going through the pex.

Cast iron rads have little resistance to water flow. The piping to get the water to a cast iron rad has almost all the pressure loss, not the rad.
At 4GPM, the rad only has about 3' of head loss(depending on style, it may have only had 1'. At 1 GPM, it has less about .25 to .5' of head loss.

Radiant loops are not ran in parallel configurations to lines of low resistance.

Your 60' pex run, only holds .34 gallon.
But, has a head pressure loss of 2' at 1 gallon per minute for its linear length, and depending on the radious of the bends, from 1 to 3' for each 180 bend. Now add 1' for each of the 2, to " reducing fittings, and your well above what a 007 can handle, and many smaller B&G circs also.

If your using a taco 007 circulator, it can't move water against a head pressure of 12' or greater.

Its possible you kinked the pex somewhere.
Its possible you don't have enough water pressure in the system.

Its more likely that since the pex isn't piped the way its suppose to be, thats why its not working.
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Old 02-13-2009, 05:35 AM   #10
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Hydronic Radiant Floor Heat


great post. Thank you!
Again, I dont know if it will work because it seems as if I can not get the air out of the line, which brings me yet again to my unanswered original question.

I know that a radiator would not heat properly if there were air in the radiator, same with the pex flooring.

Lets "pretend" for a minute that there are no radiators in the system and I just installed all pex heat. How would you bleed it?

again... what is the best way to bleed/purge out the air from the system

1. Is it correct to install a T directly at the return side of the pex connecting to the cast iron and install a bleeder on this T

2. If it is not correct, what is the correct way to bleed it out.

Last edited by KGP; 02-13-2009 at 05:39 AM.
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Old 02-13-2009, 08:02 AM   #11
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Hydronic Radiant Floor Heat


Here is a pic of how the floor is and where the T for bleeding was installed (after pic was taken)
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Hydronic Radiant Floor Heat-bath2-explain.jpg  
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Old 02-13-2009, 11:11 AM   #12
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Hydronic Radiant Floor Heat


You would need to install a shut off valve, that the water is forced to only travel one direction through the pex.

You would also need to install the bleeder set up, some where that it is always accessible.
Since after the floor is installed, you would never be able to bleed it a gain. If you ever had to open the system up for another repair of some type.
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Old 02-13-2009, 11:20 AM   #13
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Hydronic Radiant Floor Heat


Thank you. And the shut-off valve should be installed lower than the system? Like in the basement?

A bleeder has been installed and now runs into a wall that will be built over the beginning of the PVC drain system in the picture on the left side. It it T'ed into the pex where the arrow points in the picture, runs under the floor and is accessible after everything is sealed off for future bleeding needs.
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Old 02-13-2009, 01:56 PM   #14
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Hydronic Radiant Floor Heat


Not sure if you added them later but with the way the PEX is already attached I think you might have missed a critical step. You should really add distribution fins to the pex tubing to help spread the heat out. These can be bought ready made or you can make them yourself. Here is awebpage that shows homemade ones being installed in a house. You could make something similar.

http://www.builditsolar.com/Projects...Shed/House.htm

Lots of other good info on that website too.

You should also try to insulate beneath the PEX to focus the heat upwards into the floor and not let heat go to waste heating up those joist cavaties.
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Old 02-13-2009, 02:16 PM   #15
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Hydronic Radiant Floor Heat


Might be something here also http://www.inspect-ny.com/heat/Radia...t-Mistakes.htm


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