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Old 12-06-2010, 12:51 PM   #1
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Radiant floor heat questions


I have a newer home with tile and hardwood floors on the first floor. I've looked around at the various pex supplier sites and have noticed there are alot of differing opinions on what is needed (possibly because these sites want to sell you stuff). Hopefully someone here can answer some questions.

I have an unfinished basement with 31 joists at 16 oc. Each joist is 27' long. Roughly 900-1000 sq ft.

I was thinking of single line per joist of 1/2" oxygen barrier pex with homemade panels of aluminum valley flashing 8" x 10' lengths spaced 8 inches apart. Homemade panels cost $6 and premade is around $15 for less material.

Here are the questions:

Is one run per joist sufficient
Is there any reason that a thicker flashing can't be used?
Is the size of 1/2" correct
Also, some sites say don't staple the plate on both sides and some say staple both sides. Which is correct?

Any help is appreciated

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Old 01-14-2011, 10:37 AM   #2
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Radiant floor heat questions


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Originally Posted by ed2010 View Post
I have a newer home with tile and hardwood floors on the first floor. I've looked around at the various pex supplier sites and have noticed there are alot of differing opinions on what is needed (possibly because these sites want to sell you stuff). Hopefully someone here can answer some questions.

I have an unfinished basement with 31 joists at 16 oc. Each joist is 27' long. Roughly 900-1000 sq ft.

I was thinking of single line per joist of 1/2" oxygen barrier pex with homemade panels of aluminum valley flashing 8" x 10' lengths spaced 8 inches apart. Homemade panels cost $6 and premade is around $15 for less material.

Here are the questions:

Is one run per joist sufficient
Is there any reason that a thicker flashing can't be used?
Is the size of 1/2" correct
Also, some sites say don't staple the plate on both sides and some say staple both sides. Which is correct?

Any help is appreciated

I think no one has answered you yet because A) this is a difficult question and B) a lot more information is required to answer it.

In order to answer your question fully, you are going to need to do a heat-loss calculation for your home to see how much heat has to be added from the floor. Then you will have to see what the different flow rates are for each of the different materials, and how much heat can be transfered from them. You will also need to know the thickness of the 1st floor, because there will be resistance to the heat, especially if it is wood. The R value of hardwood 3/4" thick is roughly 1.05.

In general, depending on where you live, it is likely that you would not get sufficient heat from 1/2" PEX 15" apart. You may have to double it (run 2/joist) or change to a larger caliber PEX or other material.

If you want to do this right and not spend a ton of $$ on a war floor that doesn't provide sufficient heat I recommend reading a textbook.

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Old 01-14-2011, 10:57 AM   #3
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Radiant floor heat questions


The hydronic heating supplier that I use has an engineer on staff---With a floor plan and a little bit of other info--they will design a system---See if you have a good supply house near by.
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Old 01-14-2011, 06:22 PM   #4
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Radiant floor heat questions


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Originally Posted by ed2010 View Post

Here are the questions:

Is one run per joist sufficient No
Is there any reason that a thicker flashing can't be used? No as long as your not going over board
Is the size of 1/2" correct Depends on how much heat your home needs
Also, some sites say don't staple the plate on both sides and some say staple both sides. Which is correct? 1 side only, unless you lie the noise of the plates expanding and contracting

Any help is appreciated
Sometimes threads sink to the bottom on a day where a lot of people respond to threads that they get a notice a new reply was made.
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Old 01-14-2011, 08:04 PM   #5
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Radiant floor heat questions


Ayuh,... I just did a retrofit to a 100 year old cottage,...
Instead of Pex tubing, I went with the rubber stuff, Onx,.. stapled up...
It's completely Silent...
Reflextex was stalped up under the tubing, 'n the bays stuffed with glass insulation...
I pulled loops through each bay, single tube runs would Never be enough...

Here's a good resourse link,...
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Old 01-15-2011, 06:29 AM   #6
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Radiant floor heat questions


I originally installed radiant as my only heating source when I built my small house in northern Arizona, and was disappointed with the results. Ran 2 lines in every joist cavity, bought tranfer plates, insulated. Did everything required, still disappointing. I am pretty sure that my problem was installation in the basement. My original floor was 3/4" OSB. Read that that was not a good substrate for tile, so I installed 1/2" plywood on top, topped that off with 1/4" cement board, then the tile. I think that all that wood (AN INSULATOR) interferred with good heat transfer. Food for thought before getting to involved. I think that the best option is on top, either in concrete (ON A SLAB) or in that very soupy concrete mix on top of the existing wood substrate.
Good Luck,
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Old 01-15-2011, 11:49 AM   #7
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I originally installed radiant as my only heating source when I built my small house in northern Arizona, and was disappointed with the results. Ran 2 lines in every joist cavity, bought tranfer plates, insulated. Did everything required, still disappointing. I am pretty sure that my problem was installation in the basement. My original floor was 3/4" OSB. Read that that was not a good substrate for tile, so I installed 1/2" plywood on top, topped that off with 1/4" cement board, then the tile. I think that all that wood (AN INSULATOR) interferred with good heat transfer. Food for thought before getting to involved. I think that the best option is on top, either in concrete (ON A SLAB) or in that very soupy concrete mix on top of the existing wood substrate.
Good Luck,

Doubtful, or it would work.
A) did you use R-30 in all the joists as your insulation?
B) are you getting sufficient flow? What circulator did you use? Did it provide sufficient head for your layout?
C) what water temperature water are you running at?
D) where is it cold? Everywhere or just the basement? If everywhere, then your problem is certainly not the installation in the basement.
E) what is your heat loss for the house in BTU/Hr and how much heat is your system providing?

You may still be able to salvage your setup...
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Old 01-15-2011, 12:01 PM   #8
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Radiant floor heat questions


Its been serveral years since I installed it and cannot remember the heat loose and the like. Water temp was about 125 and the temp on cold mornings never got above 65 upstairs in the house. The unit had been running all night and the day before.
thanx,
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Old 01-15-2011, 01:14 PM   #9
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Radiant floor heat questions


Quote:
Water temp was about 125
Ayuh,... My rental uses 180 in the primary loop, mixed down to 150 which is sent out to the radiant tubing...
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Old 01-15-2011, 03:26 PM   #10
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Its been serveral years since I installed it and cannot remember the heat loose and the like. Water temp was about 125 and the temp on cold mornings never got above 65 upstairs in the house. The unit had been running all night and the day before.
thanx,

Wow... you gave up on it THAT easy?

Fist off, as Bondo suggests, the temp can usually be set up to 180 degrees. Not sure why you did not adjust the water temperature, since that is the easiest solution.
Second, it usually takes 3 days from turning on the boiler to achieving desired temperature via in-floor radiant heat.

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