Radiant Ceilings - 2

Jean-David Beyer

I think this may be a little off-topic for the Radiant Ceilings thread already here, so I started this one.



I have radiant heat downstairs; 1/2 inch copper tubing in an on-grade concrete slab. This system is about 60 years old and does not leak. It was suggested I start saving up for when it does leak. At such a time I will have to decide if it should be repaired, or replaced.



If it is just a joint (one of 4 Ts I imagine are in the slab), it might make sense to chop up the slab a little and fix it -- if it can be located accurately enough. But if the tubing has turned into a garden soaker, it would be crazy to try to repair that.



The alternative is something else. A heating contractor said they just installed baseboard in cases like that. But I would not want to do that because there is no room for baseboard (I have lots of floor-to-near-ceiling bookcases and other obsructions) and would like larger heat emitters so I can keep the temperature in them down for more condensing.



Ceiling radiant seems ideal. But what technology? One option is to tear out the (real plaster) ceilings, insulate above, fasten tubing (copper or Pex-Al-Pex?) up there, and replaster it? But I do not know if there are any people who do plaster anymore. If I put in drywall, should I use aluminum plates like if I were having staple-up radiant?



Or do I get flat panel radiators put up? I do not see any of those by doing a casual look on the Internet. Does it make sense to try to find some? Or will the regular wall mounted ones work OK? I worry about bleeding air out of them.



What do those who know do about after-the-fact ceiling radiant installations? (I would not propose to do the work myself.)

NRT_Rob

many options

you will need plates if you don't plaster. I don't know anyone plastering anymore either.



I like Roth Panel for overslab floor retrofits, if you don't mind a buildup and still want floor.



If the slab is not insulated, I would go with panel radiators instead of ceiling.



If it is insulated, ceiling would be ok but I would recommend some kind of finish floor.

Jean-David Beyer

I am confused.

"you will need plates if you don't plaster. I don't know anyone plastering anymore either."



Assume I have pex-al-pex for the tubing. It seems the tubing snaps into the plates. Now for staple-up the flat side of the plate is up, tight against the floor.  For a ceiling, I guess the plates will be flat side down. But how would they be fastened to the drywall? Would you glue the plates to the drywall before nailing the drywall up? Could you do that accurately enough so the plates and tubing do not hit the rafters (or whatever the horizontal beams are called)? I would hate to have to have the upstairs floors ripped up to do this. Bad enough to remove the genuine plaster ceilings.



"If the slab is not insulated, I would go with panel radiators instead of ceiling."



Why? I would have to remove everything from the downstairs in the house to do that. Panel radiators could be only about a foot wide right up at the ceiling, sort of like a moulding. I would have to calculate if I could get enough area so I could heat with the desired low water temperatures. I do not happen to know if the slab is insulated or not. The water table is at least six feet down from the slab, but not much more.



"If it is insulated, ceiling would be ok but I would recommend some kind of finish floor."



I am not sure what you are talking about here. This is all in context with replacing the in-slab tubing I already have, should it develop unrepairable leaks after 60 years. The floor is concrete with  asphalt tile glued down on it. I replaced the asphalt tile in the kitchen with ceramic tiles. When the money tree blooms, I might put hardwood, or engineered wood, in the other rooms.

NRT_Rob

because

see attached pic for plate/tubing. drywall goes over that.



cold slab, warm head, uncomfortable room. If the slab is insulated that's better. if not, panel radiators at waist height or lower would be recommended.



I would put a wood or carpet floor down if using a radiant ceiling in a basement typically. it will absorb the radiant energy better, rather than reflecting it. also, it can provide more of a buffer against the heating down through the slab and away more quickly than it can be replenished with the ceiling radiant... leading to a cold floor.

Jean-David Beyer

Picture helpful.

"see attached pic for plate/tubing. drywall goes over that."



OK. In other words, you get the plates as close to the drywall ceiling as you can get, but you cannot fasten them to the drywall (e.g., by suitable glue)? Then, by Murphy's law, there will be an air gap between the plates and the drywall. Will this not compromise the efficiency of the installation? I assume you use thick plates, not some Chinese cheapies, right? I would want them to conduct as much heat as possible and remain pretty flat.



"I would put a wood or carpet floor down if using a radiant ceiling in a

basement typically. it will absorb the radiant energy better, rather

than reflecting it. also, it can provide more of a buffer against the

heating down through the slab and away more quickly than it can be

replenished with the ceiling radiant... leading to a cold floor."



My slab happens to be on the ground floor of my house (no basement), and carpet makes sense there. I am not overly concerned with cold floors, because the floor is never really warm anyhow. Due to outdoor reset, if the thermostat called for heat, 75F water would go into the floor (55F outside). On design day (14F), 109F water would go in there.



I wonder if my existing 60 year old system will last another 40 years without leaking. I do not expect I will last quite that long, so it will be someone else's problem.

NRT_Rob

there is no air gap

drywall screws right through the plate to the strapping. they screw drywall to within an inch of its life.



we use a locally made lightweight plate. as I mention in the other thread I can get all the output I've ever needed out of the ceiling with this detail for heating. I'm not convinced other methods are superior enough to warrant the extra cost. When you're just fighting a piece of drywall it's not hard to get good output.



I think you should be making your plans now.

Gordy

JDB

Check out Dans Library go under Older Radiant Systems, and mull around you will get a feel for how things were done in that era. Lots of good stuff.



There are still plasters out there I actually have one In my area I went to school with. He is very good, but it comes with a price.



Gordy

Mark Eatherton

Critical path method question...

Rob, why no insulation before the strapping and plates?



I've found that the easier I make other peoples jobs, the easier my job gets.



Insulation is a tough enough job without having fixed resistance and sharp edges to deal with,,,





Many contractors don't understand the changes in the critical path method associated with the installation of hydronic radiant heat. I always give new contractors a letter explaining what has to be done when (i.e. insulation in certain areas prior to other areas needing insulation) with radiant hydronic heating. It avoids the "You never told me that" syndrome.



Just wondering.



ME

NRT_Rob

that particular pic

doublepost.

NRT_Rob

that particular pic

was done in a friend of mine's house who is a builder several years ago. I wasn't as quick on the trigger then to pre-inform.



I'm not exactly sure when he put the insulation in.. I know he did, but I can't imagine it much fun, you're right. makes for a good picture though, eh?



Interestingly, in our own shop we did blown cellulose above first and that actually complicated the installation of the tubing a bit. not too badly, but we used plastic to keep the cellulose up (warm side of insulation, it's ok) and it actually made it pretty tight on anything going over the strapping. we did that because we know in our shop we'll be taking down the ceiling someday to change our radiant ceiling configuration and we didn't want all our insulation to fall out when we did!



would have been more ideal to install tubing, plates, drywall and then blow the cellulose in. Course the drywallers want it warm for their goods too, so it's always tricky knowing what the best order is.

MikeG

Source of Plates

I'm actually in the early stages of doing a ceiling in a utilty room 12x15 as posted in the other thread.  I'm putting in the insulation, then 3/4 strapping.  I had to do the strapping to solve some other issues.  I'm trying to find a source of the thin flexible plates.  You indicated you have them locally made.  What are the dimensions and material thickness?  Anything I find around here are too stiff.  I will get them made if I need too.  Do you use 3/8 or 1/2 PEX?  I will probably go closer than 12", but I have to work around some can lights and other obstacles.  The floor is a slab, but 2" extruded foam on perimeter and under.  There is some copper burried in the gravel fill under the slab.  I was thinking of running the water through ceiling then through the slab.  I have concerns about the life span of the copper in the floor, but my piping install will allow me to abandone that if needed.  Obviously if more of the ceiling is coverd with plates behind the drywall the better, but what have you found to be suitable for spacings?   Any advice is greatly appreciated.    Thanks  Mike