Copper or pex pipe for heating transfer plates?

Delbert Nicks

Hi: I am a home fixer and we want to put in a hot water hydrnic heat under the wood floor of our home. We got some information on heat transfer plates and it is says to use pex pipe. What I would like to know is could you use 1/2 inch copper pipe instead and would it heat the house with less heat as copper gets hotter and should transfer faster. Also could the transfer plates be spaced at a wider space and still get good heat in the house? I will do the soldering of the copper so that is not the issue. Would like to hear some feed back on this if any one has done this.
Thank you for your time.

Delbert

hot_rod

some ideas

Before you start your installation, do a room by room heat loss calculation. For your convience there is a free calculator, courtsey of Slant Fin, right on this site.

This will tell you how much heat you need to supply to each room. With this figure, and some other info regarding floor coverings, you can determine the amount of transfer plate you will need to heat your spaces.

Copper is by far a much better conductor, virtually no temperature drop from the fluid inside to the outside wall wall of the tube. A study by Watts Radiant show 1/2 PEX with a 4.848 temperature difference between fluid and EPDM rubber at 13.098.

The trade off is the labor and hassle factor of bending and splicing the copper, from a contractors standpoint.

I think, with copper, I would consider a reset control or constant circ to avoid large, quick, temperature swings that could lead to noise problems in the plate or attachments. And design the system to provide the heat at the lowest water supply temperature. This may equate to more plates. Generally my systems use plates at 8" on center which is two, side by side, in the joist bay. Again an accurate calc and design will spell all this out for you.

Pay a contractor, or a supplier to help you with a calc and design, at least, for a comfortable, troublefree system.

hot rod

Dan Peel

The PEX (PAP) advantage

Transfer plates are good at delivering heat more evenly to a broader surface area between tubing runs. It gets very tough when using copper to retain heating capacity in the water for very far down the run. One of the greatest advantages with PEX is it's ability to carry hundreds of feet with controlled temperature drops. Go really short runs if choosing copper - with or without plating. Like Hotrod says - get the heat loss math first. Enjoy.....Dan

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Mark Bagdon

Wood shrinkage

Is there an issue of shrinking oak flooring and opening up larger cracks between the boards with radiant heat?

Mark

Mike T., Swampeast MO

Bad things about copper in plates:

1) It's a PAIN to install. The better the plate grips the more difficult to install.

2) You likely won't find engineering data for this construction and you have to make "guesses" and extrapolations.

3) High conduction shouldn't be used as a means to decrease spacing (use less plates/tube). Instead, use it as a means to work with lower temperature. In some constructions it might be the difference between return temp in the condensing range 80%+ of the time vs. 20%- of the time.

4) Prepare for extreme delta t. At cold start the delta t may remain infinite (i.e. ambient) for a LONG time. Once the system achieves maintenance, delta t becomes much more reasonable.

5) Individual run length is greatly dependent upon how the system is controlled. Maximum run length is available with systems both reset and constantly circulating. A non-reset, digitally controlled system would require extremely short runs. While they may exist, I'm unaware of any calculations for this effect.

Good things about copper in plates:

1) No special tools required for fittings.

2) No concern with oxygen diffusion.

3) Very well-proven material life.

4) Great for utilizing an EXISTING supply temperature too low for other underfloor methods.

I'd use this method system-wide if:

1) I'm a DIYer with time and patience who wants to do his own tube install. (Study, study, study or confer with a pro for design.)

2) I didn't trust PEX.

3) I wanted a fully condensing boiler but a PEX system would result in temperatures too high to fully realize potential savings of such.

hot_rod

Depending on the install

The copper can be easier. I built this copper ThermoFin assembly on a concrete floor. You can actually handle a 20 foot stick of copper, with the fin pounded on. I grabed the assembly, mid-span and used zip screws to fasten to this metal ceiling. I did predrill the fin to lessen the amount of push on the ceiling, overhead.

On this job I used PAP to connect the loop ends. Since then I have purchases a REMS Curvo bender. Now I bend the 20 foot copper in the middle.

Using a REMS Hurrican, I can quickly swedge the copper ends without softening the tube. This also speeds up the copper radiant work

hot rod

Mike T., Swampeast MO

WOW!

Hope I'm seeing that correctly...

Floating slab floor with metal below. Is this a combined radiant ceiling/floor application?

What an efficient and appropriate use of material!!!!

Mike T., Swampeast MO

Thermofin

Has Radiant Engineering come out with new engineering data or did you put that IR thermography test to VERY good use?

hot_rod

actually

this is a ceiling. That metal panels are fastened to the bottom chord of the truss. I'm not sure if this is ceiling radiant or a giant panel radiator! The shop is well insulated with 12" of cellouse installed above the metal panels.

I ran this, along with a slab radiant in the rooms adjoining this shop. A Polaris running 120 kept this 24 X 18 foot shop at 60 F all winter. In addition to 3 bays of radiant slab. Very low fuel cost, compared to the previous unit heaters.

hot rod

Mike T., Swampeast MO

Looks sort of like non-perforated aluminum soffit material?

Is it a "warm feeling" 60°?

Cosmo

Looks interesting....

What do you figure on heat output per linear foot of copper/thermofin? How warm does the steel panel get?

Cosmo Valavanis
Dependable P.H.C. Inc.
Plumbing Heating Cooling