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Insulating Radiant Heat Coils

Barb Member Posts: 18
Brad...thanks. Let me take this piece by piece.

Yes, I was referring to the tubing. My house had a beat up floor, so on top of the old pine, which probably had it's own sub-floor, tho maybe not, I had oak put down. I say that cuz I'm also trying to understand why the heat doesn't transfer up that well. It's also the part of the house that faces the north; which has a very sketchy foundation under the front part. Otherwise the rest is as you described.

I think part of the problem is that I didn't put enough aluminum plates, but I have a whole box left over, so I'm going to fix that. Should I try to cover the ends some other way, cuz my plates have a groove and won't work on the curve? Should I try to make sure the whole area between the joists is plated?

I get what you're saying about leaving a space for the conductance of heat. Are you saying I'm losing effectiveness because of the horizontal position of the insulation. I imagine the old floor most certainly is giving off dust. As for air currents, well I mentioned there have been plenty, but I think I can reduce that significantly....I'm just not sure how yet. Some of my foundation in the front is dirt. I was thinking of putting up a brick wall inside the so-called outer wall, but don't know what to fill the space with. But I'm not up to that yet, and don't want it to get me stuck on what I can do. Any ideas?

As for the moisture of each floor, my basement takes water in every time it rains, and not just a little! I guess that speaks to the plastic being helpful. Yes?

OK, now for the purge. I was told to increase the pressure on the boiler to 30 lbs....I don't know how to do that. Is it simple enough?

Yikes! You lost me a little on the boiler. I do know, at least I'm pretty sure, that my boiler heats the water to 180 and then my IPC panel mixes it with cold water to reduce it. I don't know what flew gas dewpoint is. I do know that they didn't have the model right for my house, so I ended up with one 2 or 3 sizes too big. Now, in addition to costing a lot, it's apparently creating too much heat, and is leaking water from the steam build-up...I think that's what they said. I just checked, and found out my efficiency rating is only 8.2, which was quite low on the scale they showed. I have a CGa-8.

While I'm on a roll, what temp would you run at - I have one floor like I described, and two floors where I put the coils on top of the sub-floor, filling the space with 3/4" plywood, with plates coving most of the tubing. Yeah, I know, I didn't do it right, but it was the advice I got at the time. I'm looking for the most efficient answer that is the most reasonably priced.

Over and out.


  • Barb
    Barb Member Posts: 18

    OK, I'm about to rework some coils in my radiant heat system. Once that's done, I want to insulate it. I'm putting the coils "up under" the first floor.

    I know when you insulate your house, you want to leave a space between the exterior wall and the insulation to create a pocket. Is the same true for radiant heat coils, or should I put the insulation right next to the coils (or to be more precise, the aluminum pieces that cover the coils)? Once that's done, would it help to put plastic (I have a bunch of really thick stuff). I want to keep the insulation from falling into the basement, but wondered if it would also help hold the heat in. I also wonder if it will just disintegrate over time.

    Once I'm done, can't I just open the loop again to let the water back in, and then open the valve at the manifold, to let the air out?

    Any thoughts on the best choice for a boiler that runs the most efficiently? I currently have a Weil-McClain....does that matter?

  • Brad White_203
    Brad White_203 Member Posts: 506

    When you say, "coils", and from the context of your post, I assume you mean tubing attached to the bottom of the sub-floor, between joists, with plates. Is this correct?

    I specify an air space, usually at least two inches. This is to allow a more even temperature across that plane. If you "snugged it up" or sprayed foam on the entire width, you would isolate your conductance and have more "striping" or detectable warm and cool lines on the floor.

    The notion of the air space is to allow emittance of infra-red radiation. It needs air or at least a non-solid material (such as the vacuum of space) in order to transfer. That air space allows that and shares/evens out the temperature.

    Reflectivity is a part of this, same as for the foil backing on batts between studs. If the drywall is tight to the foil (batts installed flush and not recessed with the tabs on the inside edges), that potential is lost, roughly an R value of 1.5.

    As a practical matter, batts in the horizontal with foil-side up have been shown on this forum to "dust over", negating that radiant component, but I would still leave the air space. Key to all of this is how airtight the installation is below though. If there are air currents making their way below and around the batts (batts are not good air barriers), you are losing insulation effectiveness.

    The use of plastic below as the air barrier? Too many variables. If your heated space holds more moisture and the basement is below the dewpoint, you will condense on your plastic. If the upstairs/downstairs conditions are similar, I would not be so concerned.

    The "open the loop to let water back in" issue: You really need a purge, a high velocity flow to force out air with the water until it runs clear. One circuit at a time. Velocity is your friend here.

    As for boiler, the brand name means less than the model and how it is applied. Sort of like saying that General Motors makes the right car for you, without knowing your needs.

    Regardless, if radiant, you seek the lowest water temperatures which will do the job (same as for any job), but in this case well below flue gas dewpoint. Your boiler either loves low temperature return water (a modulating condensing boiler), or it is a cast iron or other non-condensing boiler and needs protection all the while providing low temperature water to your floors.
  • Brad White_203
    Brad White_203 Member Posts: 506

    I'd like to reply now but would rather do so off-line maybe later tonight. Drop me a line at my e-mail address above (encoded such as it is). I will be happy to help but by all means, others may chime in too and that is a good thing.

  • Barb
    Barb Member Posts: 18

    I can't seem to figure out your email.
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