Radiant floor water temp


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Old 01-13-16, 01:15 PM
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Radiant floor water temp

Hi - I have an upstairs bath that my heating/plumbing contractor is about to lay 1/2 pex that will get concrete with tile on top. He is using the existing supply line that come off the boiler. As an interested "hydronic nerd" I always thought you had to mix the return to lower the water temp for radiant.

When I asked him how he was going to do that he looked at me as if I had 3 heads. He said you don't lower the water temp and that the flow rate, pex material, area of the loops are what contribute to the floor and room temp. The new radiant floor will be on a zone with a baseboard and 3 other radiators - so I'm happy if we don't need to figure out how to get the water cooler for the floor. But everything I've ever read said that you need to lower the water temp for radiant. Also my other radiant floor from the eighties in a first floor slab looks like it gets mixed with return water at the boiler.

So does this guy not know what he is doing or am I missing something?
 
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Old 01-13-16, 03:25 PM
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So the next time the heat comes on go and feel the pipes feeding the radiators...pretty hot...120* is about the maximum water temperature I run for tile floors...more than that will be uncomfortable to walk on..the radiant should be zoned seperately and a mixing valve will bring the temperature down
...Tell your"heating contractor" to do a little homework...Google is your friend
 
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Old 01-13-16, 03:38 PM
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I always thought you had to mix the return to lower the water temp for radiant.
Yes.... that is the correct way to supply water to them.
 
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Old 01-13-16, 04:18 PM
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Yea - I said "wouldn't the floor then be as hot to the touch as the radiators get?"

He said that because of the number of loops and the size of the PEX (1/2") that the floor would never get as hot as the water in the tubes.

There is no such thing as PEX tubing with different thermal transfer properties? He is using PEX to run domestic to my sink in the same floor and he said it was a different kind of PEX that won't be impacted by the heat of the floor. So could the radiant floor PEX lines be of a type that doesn't give up 100% of its heat?
 
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Old 01-13-16, 04:21 PM
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So could the radiant floor PEX lines be of a type that doesn't give up 100% of its heat?
No. It sounds like your plumber is taking the easy way out.
 
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Old 01-13-16, 10:44 PM
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So does this guy not know what he is doing or am I missing something?
I do not think you are missing anything.

Non-condensing boilers need protection from cold return water and condensing boilers need cold return water.

idronics 12:Hydronic Fundamentals [pdf]
[page 43, pdf] PEX Tubing
[page 36, pdf] CONVENTIONAL BOILERS [non condensing]
[page 57, pdf] RADIANT PANEL HEATING
[page 58, pdf] HEATED FLOOR SLABS
[page 59, pdf] HEATED THIN SLABS
[page 60, pdf] ABOVE FLOOR TUBE & PLATE RADIANT PANELS, BELOW FLOOR TUBE & PLATE RADIANT PANELS
[page 80, pdf] CONTROLLING HEAT OUTPUT FROM HEAT EMITTERS


idronics 7: Mixing in Hydronic Systems [pdf]
[page 3, pdf] EARLY APPROACHES TO MIXING
[page 6, pdf] MIXING FUNDAMENTALS, PURPOSE(S) OF MIXING Preventing sustained flue gas condensation [boiler protection]


MODERN HYDRONICS February 2013 [pdf] www.hpacmag.com
[page 4, pdf] That Sinking Feeling Do not let a cool slab dominate your panel radiators. [Slick use of a smart three-way valve]
[page 6, pdf] Don't Just Go With The Flow Creating hydronic radiant equipment schedules is the key to successful radiant projects.

Radiant Floor System Design. Chapter 8 [pdf] uponorpro.com
[page 67, pdf] Floor Surface Temperature Limitations
[page 68, pdf] Step 8: Supply Water Temperature

[Radiant] Installation Methods Chapter 6 [pdf] uponorpro.com
 
 

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