# Hydronic Radiant Floor Heat



## beenthere (Oct 11, 2008)

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.


----------



## JohnH1 (Jan 9, 2009)

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.


----------



## KGP (Feb 12, 2009)

beenthere said:


> 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.


----------



## KGP (Feb 12, 2009)

JohnH1 said:


> 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. 

:thumbup:


----------



## beenthere (Oct 11, 2008)

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.


----------



## KGP (Feb 12, 2009)

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.


----------



## JohnH1 (Jan 9, 2009)

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.


----------



## beenthere (Oct 11, 2008)

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, ¾ to ½" 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.


----------



## KGP (Feb 12, 2009)

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.


----------



## KGP (Feb 12, 2009)

Here is a pic of how the floor is and where the T for bleeding was installed (after pic was taken)


----------



## beenthere (Oct 11, 2008)

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.


----------



## KGP (Feb 12, 2009)

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.


----------



## Dragon (Aug 1, 2006)

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/SpaceHeating/SolarShed/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.


----------



## Gary_602z (Nov 15, 2008)

Might be something here also http://www.inspect-ny.com/heat/Radiant-Slab-Heat-Mistakes.htm


Gary


----------



## KGP (Feb 12, 2009)

Dragon said:


> 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/SpaceHeating/SolarShed/House.htm
> 
> Lots of other good info on that website too.


Thanks for the link. interesting. I use the bubble insulator on top of r-13 but did not put these plates... never saw that before.



Dragon said:


> 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.


I did insulate in between the joists keeping the heat radiating UP and heating the joist and floor rather than heating that whole cavity like you said, but thanks for the reminder.:thumbsup:


I think I am just going to focus on completing the rest of the bathroom to get everything sealed up. I know it is installed and have a bleed accessible for latter should I need it. After the room is back in working order, I can mess around more when I start the lower floors radiant system using the proper pump and running a proper manifold eliminating the rest of the house's radiators.


----------



## beenthere (Oct 11, 2008)

Pex/radiant systems need to have a purge set up, not a bleed set up.


----------



## KGP (Feb 12, 2009)

so leaving it the way it is and coming back to it, to complete the rest of the radiant heat system correctly after the bathroom is put back together would be ok?


----------



## beenthere (Oct 11, 2008)

If you install a purge system.
And, seperate it from the piping to the other rad/pex you install for the room below it.


----------



## beenthere (Oct 11, 2008)

See Drawing.

Circ was only put on return line for ease of drawing, not for where it has to be.


----------



## KGP (Feb 12, 2009)

Thanks for the drawing. I will be revisiting this after I finish the room. I appreciate all the time you have spent answering my idiotic questions.  

I was however looking through an expensive ($200!!) book I got called Modern Hydronic Heating by John Siegenthaler where is says that I can infact run the radiant floor heat off of the same system as my radiators. What it says to do is to use the return side going to the boiler to feed the pex. Obviously I would still need some other componets, but this addresses the issue raised by John about the temps being different requirements for radiators and radiant floor... If the pex requires less heat, utilizing the return water where the heat has been exchanged out of if by the radiators, the temp would be lower... sounds logical to me. What do you think?


----------



## beenthere (Oct 11, 2008)

Yes, that method requires adding a circulator, and a few other controls.

There are 2 basic different ways to set that configuration up.

But, if your doing the whole house in radiant, or a large portion, then its better to do a full manifold and mixing set up.


----------



## mark '87 930 (May 2, 2011)

*realizing this is an old thread..*

I was wondering what the solution was and if you were able to get it to work finally? I'm in the middle of doing exactly the same thing (literally).


----------

