Radiant floor heating ?


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Old 01-26-11, 11:09 AM
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Radiant floor heating ?

I am seriously thinking about removing my baseboard on the first floor and going with radiant floor using PEX and transfer plates. All the baseboards need replacing and they get in the way of furniture placement.

I am curious at how effective the heat will be installed under the sub-floor and can I just hook the pex to the existing copper that went to the baseboard in each area?
 
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Old 01-26-11, 02:25 PM
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Under the subfloor doesn't sound very effective to me.
 
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Old 01-26-11, 02:54 PM
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It is effective.
You need to create a sealed 2" x the width x length of joist space and insulate well under it to get the heat up.
You need to mix the water temp down to about 100- 140 depending on the heat loss.

You will enjoy the comfort way more than copper tube rads.
 
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Old 01-26-11, 03:35 PM
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Bummer

That means installing a manifold and extra piping.

I was hoping that the 200 degree limit PEX would be good enough to just hook to the existing copper already there.
 
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Old 01-26-11, 03:55 PM
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Dont waste your money on the radiant with transferplates. Your installing from the crawl or basement??? If your going to do it, then use something like this. Install on top.

Watch video
A5060701 - Uponor (Wirsbo) A5060701 - Quik Trak 7" x 48" Trak

Is your element still good in the baseboard??? Just replace the covers. I was replace my covers as I renovated and was able to raise them 2-3 inches for better air flow.

Mike NJ
 
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Old 01-26-11, 03:57 PM
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You need to make sure you will get enough heat out of the floor to make sure it will make up for BTU's lost. You will have to make calculations for this. You may find that you will still require some baseboard.
 
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Old 01-26-11, 05:25 PM
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Oh if only radiant was that simple.

It's not hard to get right, but it's also easy and very expensive to get wrong.

First, do a heat loss to figure out how much the room requires. You can get around 25 BTU/hr per square foot of floor with a good radiant install. So if you have a 100 sf room you could (in the absence of furniture, cabinets, carpet, etc.) get around 2500 BTU/hr out of the floor. If the room heat loss is 4000 BTU/hr, however, radiant alone won't meet the load.

And you need to design the tube size, flow rate, tube spacing, water temperature, etc. so you get the output you need when you need it.

Then, consider your floor covering. Carpet kills radiant output. Even the so-called 'radiant-friendly' carpets really do a number on the output. Wood is ok. Tile is better.

You also need to mix down the water temperature. Putting 180 degree water into a radiant underfloor will kill your subfloor and wreak havoc on wood floors. And make tile surfaces unbearably hot.

The surface temperature of radiant floors shouldn't go above about 85F.

When you mix down the water temperature, you now need a way to protect the boiler from condensation due to the low return temperatures. Condensation is acid rain in your boiler and in a standard cast iron boiler will kill it in pretty short order. So now you have separate pumps and valves, more piping, etc. etc.

So all that said, there are ways to make little radiant jobs work. A place to start is this fine article by John Siegenthaler:

A Little Floor Warming Please

There are also so-called suspended tube radiant approaches that can use full-temp 180F water, but they are horribly inefficient and IMHO not worth it.
 
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Old 01-26-11, 06:21 PM
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Originally Posted by davper View Post
Bummer

That means installing a manifold and extra piping.

I was hoping that the 200 degree limit PEX would be good enough to just hook to the existing copper already there.
Its not the water temp limit of the pex, it's the fact that it runs at a very low temp compared to the baseboard rad.
It will condense your boiler, and unless it's designed to condense, that is not a good thing.
As for the quicktrack, its a fine solution if you don't already have a finished floor on top of it. If you do it gets expensive to start pulling out flooring and doing the upon system. I don't like the small pipe diameter much either.
 
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Old 01-27-11, 08:37 AM
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[QUOTE=
Is your element still good in the baseboard??? Just replace the covers. I was replace my covers as I renovated and was able to raise them 2-3 inches for better air flow.

Mike NJ[/QUOTE]

All the fins are damaged and the tops which are screwed in behind the elements are also damaged. Not my doing, I just bought 2 years ago.
 
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Old 01-27-11, 08:43 AM
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Originally Posted by lawrosa View Post
Dont waste your money on the radiant with transferplates. Your installing from the crawl or basement??? If your going to do it, then use something like this. Install on top.

Watch video
A5060701 - Uponor (Wirsbo) A5060701 - Quik Trak 7" x 48" Trak

Mike NJ
That's great but I have brand new hardwood and tile floors.
 
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Old 01-27-11, 08:53 AM
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Thanks for the info

Can I do my own heat loss calculation. I am assuming it is a standard formula based on the variables of the room.
 
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Old 01-27-11, 04:20 PM
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slantfin heat loss calculator program here:

Sullivan Supply Co., Inc.
 
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Old 01-27-11, 04:52 PM
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I'm a newbie around here, and have had my share of difficulties with my radiant system, but only because I have recently switched from propane to vegetable oil. I read and am searching for a link to a Department of Energy report that indicates that staple up aluminum transfer plate radiant floor heat really is a good way to go. I will put it up as soon as I find it. We are using water at approx 135-140 degrees in our system, yielding a floor temp of approx 85 degrees. It feels great, and my twin babies walk around without socks all winter long. We made our own plates for approximately $0.20 each with simple hand tools. Check your local metal suppliers for dead soft or 50% soft aluminum sheet, approx 18-16 gauge. Cut into rectangles with a shear or tin snips, or a paper cutter for that matter. Screw a section of your pex to the wide side of a 2x4, attach to a hinge so that it fits between 2 more 2x4, and you have a stomp press to make your plates. I would suggest using a strip of tyvex between the plate and tube to minimize squeeks during expansions and contractions. We used a pneumatic stapler to install. I would suggest using the smaller diameter of pex. We used the 3/4 to minimize install labor, but in reality the larger diameter is harder... bigger holes to drill, easier to kink, etc. We have temperature "striping" due to the smaller amount of tubing in the floor.

Sorry for the long post. I can share more if you want later . Radiant systems don't need to be complex or expensive. We managed just fine for 6 years using our propane water heater to heat our 2000sf house.
 
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Old 01-27-11, 05:33 PM
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One more thing... we installed under approx 1.5" of subfloor and underlayment, and have cork, forbo linoleum, marble and ceramic flooring. As long as the r-value of your underfloor insulation is greater than the r value of your flooring materials (R-Values of Different Flooring Materials, Floors, Flooring, R Value) you should be okay.
 
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Old 01-27-11, 06:26 PM
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Screw a section of your pex to the wide side of a 2x4, attach to a hinge so that it fits between 2 more 2x4, and you have a stomp press to make your plates
Yankee ingenuity at it's finest!

I thought for sure you were gonna say that you cast them out of copper!
 
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Old 01-27-11, 08:17 PM
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Originally Posted by forgedcu View Post
Screw a section of your pex to the wide side of a 2x4, attach to a hinge so that it fits between 2 more 2x4, and you have a stomp press to make your plates.
I'd like to see a picture if you have one.
 
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Old 01-27-11, 08:23 PM
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yankee ingenuity at it's finest!
lol!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
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Old 01-28-11, 08:54 AM
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Here is a pic of a similar rig. I just added a small bit of 2x4 across teh back and attached the top part with a hinge to make it go faster. My wife actually made and installed all of the plates while I soldered the manifolds.
 
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Old 01-28-11, 09:30 AM
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This sounds like a fine DIY project, but it should be noted that there are two sorts of aluminum plates - the thinner, stamped ones and the thicker, extruded ones. I used the thicker plates with my wooden floors. These plates are thinner plates, by virture of the fact that you can make them via stamping, and the transfer of heat is "not as good" as with the extruded plates. If you are running a geothermal or solar heating system (I have a solar heating system), and you are obsessively concerned about water temperatures and have the control system to take care of that (I am, and I do) than your best bet would be to use thicker plates, albeit at a higher cost. This is especially true if you are going to mount the plates under the subfloor rather than between the subfloor and the finished floor.

Nonethless, this looks pretty interesting.

Jeff
 
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Old 01-28-11, 02:36 PM
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These plates are thinner plates, by virture of the fact that you can make them via stamping, and the transfer of heat is "not as good" as with the extruded plates.
Can you point us to some empirical data that supports this?

Not that I'm doubting you, but I should be from Missouri!
 
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Old 01-29-11, 01:04 PM
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Thicker plates are just a better heat sink.

Thinner plates are most often used in part of the floor assembly (i.e., in the sandwich, such as with Warmboard or a homegrown sandwich). Thicker plates more often under the subfloor.

Not to say that thinner plates can't be used under the subfloor....
 
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Old 02-01-11, 07:19 AM
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I have a feeling the difference between the two plate thicknesses is not enough to justify the added cost and physical labor on installation in a staple up system. With the thinner dead soft aluminum, you can custom cut plates for the end of runs, or anywhere that you want extra passes of pex for added heat concentration (we doubled up on my wife's side of the bed, outside of the tub, and under the drip dry area of our laundry room, for instance) Also, you can cut smaller pieces and form by hand against the subfloor on curves. RE Michel has the thicker heat plates listed at $14 each... after discount that is still nearly $8 each. Yeouch! I bought a whole 3x8 sheet of aluminum roughly $22, and that made a whole bunch of plates. To increase the efficiency of the system, create the 2" space under the plates mentioned earlier with a reflective material, (bubble foil works great, but is pricey, we used a reflective tyvek type material and regular fiberglass batt under it)

Run the tubes and staple up a few plates as you go, then go back and fill in the spaces with more plates, staple up the reflective barrier between the joists leaving a 2" air space, and then staple up the insulation. Remember the strips of tyvek between the plate and the tube to avoid squeaks. Here is an example of installation instructions:

http://www.radiantcompany.com/manual...l_web-2009.pdf
 
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Old 02-01-11, 08:33 AM
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The difference in plate thickness does not account for all, or even most, of the difference in efficiency. The efficiency difference is a result of the grip of the aluminum plate on the PEX tube, the amount of actual surface area contact. In heat exchanger land, surface area is king. Having a plate that not only grips 3/4 of the circumference of the tube rather than less than half, but also grips it with a firm seat that requires work to bang in rather than the simply drop the tube into the furrow is what makes the difference, and you won't need Tyvek or some other solution to prevent expansion squeaking.

You will pay for the tubing one way or another. If you put in less expensive plates, you will need to run warmer water temperatures to get the desired heat output from a given run, and you will therefore have lower delivery efficiency and lower combustion efficiency. Don't get me wrong here, it's a matter of cost and benefit, but you will pay one way or another.

Also, reflective insulation under tubing is junk. Put the plates in under the floor and then insulate underneath. You'll get far more benefit with the extra 2" or 3" of fiberglass (or whatever) than you will with air and and reflective barrier. Hopefully, your water temperatures won't be warm enough to benefit from reflective foil. If they are, you have a serious design problem there.

Jeff
 
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Old 02-01-11, 04:32 PM
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I do agree with Jeff's statement about the 'grip' of the plate. That would be CONDUCTIVE heat transfer. If the plate fits loosely, of course it stands to reason that not as much heat will be CONDUCTED to the plate... and even LESS will be conducted if there is a wrap of Tyvek material between the tubing and the plate.

We must realize that 'radiant' heat depends heavily on conduction. The heat is conducted from the water in the tubing into the plates, then conducted from the plates into the floor assembly. The heat does not become RADIANT until it radiates from the floor.

Therefore, the more efficient you can make the conductive part of the process, the more heat you will be able to get from the floor...
 
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Old 02-01-11, 04:40 PM
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On the other hand, as long as the underside of the floor assembly is properly insulated, you won't actually be LOSING anything in the way of BTUs... the heat that isn't conducted to the floor simply travels back to the boiler, right?

What you might LOSE is system RESPONSIVENESS... in other words, it won't react as quickly because less heat is being drawn from the water.

You MAY have to run the water a bit hotter to regain that responsiveness, which WILL cost a few bucks more.

I guess the real question then becomes:

How long do you have to run the system before your LOSS exceeds the difference in price of the plates? 20 cents versus $8 ... my guess is a L O N G time! You could purchase a whole lotta fuel with that $7.80 times the number of plates used.
 
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Old 02-01-11, 05:23 PM
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As I said earlier, I do not think that it's appropriate to speculate on "how much money is to be saved" without doing any sort of analysis. You can't make a guess based on "$8 versus 20 cents" if you don't know what the area is, or how it affects the return water temperature, or what the control system is, or how much heat is lost through the piping. You have simply stuck your finger into the air and waved it around a little and come out with a pronouncement. That's bad engineering. You would never do that if someone asked you to pick a boiler size; why would you do that if someone asked you to pick an emitter?
 
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Old 02-01-11, 06:25 PM
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Nobody asked me to do anything! Just like nobody asked you! ... I'm just sayin'... I could buy a whole lotta fuel with the money that could be saved on the plates... and why isn't it "appropriate" to speculate? That's all we can do after all, is it not? You nor I are there to make the measurements and take the data...

I didn't make any kind of "pronouncement" one way or the other, just a bunch of guesses. Why can't I guess? That's my right, no? Ultimately what people do is up to them!

So, let's find out some of the variables... Forged, how many plates did you make?
 
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Old 02-02-11, 07:39 AM
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We used over 700 12x18" plates, although some additional plates were used, the specialized ones that I mentioned in my earlier post. I spent approximately $220 on the metal, but I kept a couple sheets to use as wall protection behind my forge, and also cut up one into several smaller pieces to use as solder shields, and I still have two left. I did shop around for the metal to find the cheapest rate, and that price is at 2003 market rates. The metal is very light, and it was a bit of an odd lot in that it was dead soft, so the price was fairly low. Half hard material is more common, and is probably easier to work with.

I need to reiterate though, that I really didn't install more than 3% of them... my wife did all of that work while I made the manifolds. That is another beauty of the thin plates. It is easy to handle them, and there is no specialized assembly methods required. Because we used a section of the exact tubing used in the floor as a forming mandrel, the fit was very tight.
 
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Old 06-23-14, 03:27 AM
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If you want to be sure there are no noises from the metal plates cue to expansion and contraction. Staple your fins within one inch of the pipe so most of the movement will be beyond the staple. Then insure that none of the plates edges are touching anything. wherever they are fold the out of the way a bit leaving a 1/4" or so. You shouldn't hear a single creak from that floor.
 
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Old 06-23-14, 04:59 AM
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Thanks for the additional response. This thread is 3 years old and is now closed.

Please start a new thread...

Thanks...............
 
 

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