Radiant Method

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mtnxtreme

Member
Jan 22, 2007
118
Doing a new radiant system over 3/4 Advantech, in the past I’ve installed 5/4 sleepers, installed tubing, poured sand and cement mix over top then plywood or tile board to sleepers, it’s worked well, but it’s been awhile so wi seeing if there’s something better out there today ‘
 
Doing a new radiant system over 3/4 Advantech, in the past I’ve installed 5/4 sleepers, installed tubing, poured sand and cement mix over top then plywood or tile board to sleepers, it’s worked well, but it’s been awhile so wi seeing if there’s something better out there today ‘
If you go by John Siengenthaler's recomendations, you skip the radiant floor and go with radiant walls and ceilings using either the prefab WIsbro channel tracks or a home brew version foil faced isoboard and 1/2" plywood with 3/8" tubing covered with drywall. He makes a lot fo good engineering arguments for this approach.
 
Well we have radiant in basement slab so utilizing that heat, and then 1 st floor should have us covered, can’t go ceilings they are cathedral T&G and one wall is all glass so walls won’t work. Is the floor tubes in lightweight cement still a good way or just sandwich tubing in an open channel without cement and or metal plates etc ?
 
it depends on your system water temp. If you're running 120F or hotter then just about any method will work. Many people want to run a lower water temp to increase efficiency or because they are using a heat pump or have wood floors or something, in that case the thermal contact between the floor and tubing matters a lot more. I think the poured cement or aluminum transfer plates are both fine options. Another way is to just use a narrow tube spacing 8" or 6" centers then you have nothing to worry about regardless of whether you used the plates or not. But with more tubing you have to watch out to keep your loop length under 300' if you're using 1/2" pex or 150' for 3/8".
 
Its going to be a geo thermal system, I would love to not have to pour cement again, and less weight !
 
Ok if you don't want to pour cement I would get the aluminum heat transfer panels like these, First install your sleepers then staple the panel to the sleepers then install the pex in the channel. Lay your flooring directly on top of that.

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Ok if you don't want to pour cement I would get the aluminum heat transfer panels like these, First install your sleepers then staple the panel to the sleepers then install the pex in the channel. Lay your flooring directly on top of that.

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Who makes these ? What do you think these plates versus your suggestion of doubling up the tubing ? And what about the thermal mass of the cement, you think it's a big plus ?
 
Who makes these ? What do you think these plates versus your suggestion of doubling up the tubing ? And what about the thermal mass of the cement, you think it's a big plus ?
As Peakbagger said the thermal mass isn't too important unless you have a really intermittent heat source like a wood boiler.
I guess with a heat pump it could be useful as a buffer to reduce cycling, but if you're just filling in between plywood with lightweight cement there won't be that much added mass anyway so I doubt it'd make a difference. Your goal is really just to have good thermal contact from the tubing to the floor.

I have installed a radiant floor in my house with 3/8" PEX 8" on center with plywood sleepers and NO transfer plates. It works fine, plenty of heating capacity but I do notice some cool spots so I can sort of feel where the tubing is when I walk on it barefoot. Not really an issue for me but the aluminum plates can help to unify the floor temperature. Uponor makes them and I think a few other manufacturers. But those are also a racket these days cause it's really just a folded up piece of flashing. Seems like the DIY radiant craze has gotten a little out of hand and vendors are cashing in. Shop around and see if you can find something without getting price gouged too bad.
 
I havent messed with the new foam style but I think the intent of it is that in most cases, when installing radiant with or without heat shields, the unheated space under the shield is insulated. I picked up a pile of the older style that is just two strips of plywood with a shield outback on Craigslist and in my case where its going to be installed in walls, a piece of foil faced isoboard foam is going to be put inside the interior wall before the strips and tubing are installed. The drywall is then screwed into the plywood presumably into the underlying studs behind the foam. There are quite a few floor systems that are not attached to the underlying floor deck, its just sits on top of it and "floats" which is probably a good thing with radiant flooring.

Siegenthaler's (AKA Siggy)low mass method is using supply water temps down in the mid to high eighties with injection mixers on the supply manifold to keep the supply loops at low temp and I think he even uses outdoor reset to drop supply temps lower in warmer weather. He uses ECM pumps in his designs and runs them nearly continuously until the outdoor temps warm up to the point that heat is not needed. This means someone like me with a wood boiler and storage can run the storage temps down to 90 degrees F instead of 140 (from a top temp of 180) which more than doubles my effective thermal capacity. It also allows air source heat pumps and geothermal to integrate into the system as they at best currently max out at 120 F in cold weather. Note in some cases like a commercial or government building he will have two supply manifolds, one low temp manifold for the occupied spaces like offices with low mass radiant and a higher supply temp manifold for garages and public spaces where more heat may be needed quickly. In that case, I think he goes with tubes in concrete (with a lot of insulation underneath) so that something like a truck entering a garage from the outdoors doesnt pull down the space temp too low as the thermal mass will act as a buffer.

Of course, radiant designs, usually assume that the spaces are built to high thermal standard, like 2 by 6 walls with a couple of inches foam on the outside and extensive air barrier sealing so the actual space heating demands are a lot lower than a conventional house. Radiant is best to deal with space that is mostly convective loss to the outdoors, if there are drafts in the space than the space temps usually have to hotter to deal with the impact of drafts.

I do agree those new style foam panels seem to be really pricey. Since my time is free, I think I would just skip the heat shields when I run out of the ones I bought and use regular plywood strips for spacers on foil faced isoboard but on a job with contractor it may pencil out in labor savings and speed to use the all in one foam units.
 
You know I have a sheet metal shop I can make a hell of a lot of plates 8 feet long and make them so they touch the plywood above, we will be tiling these floors so they should be pretty warm.
 
We tore down our old kitchen L over a crawl space and put in a new foundation with a radiant slab over 3" of blue foam. After having the crawl space and freezing floors it's great. The thermal mass of the floor will keep the room warm all day but it does take a while to warm up if it gets cold. Run the water temp at 110 and I think if you had heat on all day probably could run it at 85 to 90 and it would be warm. After having the floor warm I can't even think about putting panels in the wall or ceiling . A neighbor built a fairly large house in the late 70's and the latest and greatest at that time was electric radiant heat in the ceiling, was a disaster.
 
Hard to compare a home built in the late seventies to minimal energy standards with modern construction. Radiant tends to work better with energy efficient construction. R value for a 2 by 4 wall is around R 4.5, 3 inches of blue foam is R 15. Odds are the attic of a seventies home was 6" at best. Trying to use electric radiant in a ceiling during that era would be a good way to keep snow off a roof. Nevertheless it was cheap and the power company would subsidize electric resistance heat and give the homeowner a "gold medallion" for the front door to show off it was an "all electric home"

Builders in the seventies actually tried to avoid things like air barriers as they wanted a house to "breathe". I do remember when my dad was finishing a second floor into bedrooms in the early seventies he was warned not to put in plastic and when he wanted insulation for the ceiling 6" was the absolute maximum recomended.

The concept of heat rising does not apply with radiant heat, its line of sight. Radiant floors make sense in some areas like kitchens where wall space is limited but in most spaces, radiant walls work as well or better. In most cases, the supply temps can be lower using radiant walls as the thermal mass is lower in the wall.
 
Not comparing anything just what little I know, I'm far from an expert but I do know that the only thing cheap about that radiant ceiling was installation bills were very high and that's when power was cheap and they almost instantly stopped using it and went with oil hot air.
I've read, probably from experts, that with radiant floor the warmest air is near the floor and gets cooler as you go up and with ours that seems to be true. So does that mean that now on a radiant ceiling it does just the opposite? Just kinda wondering.