Replies

1. 
   johnnyd | Jun 30, 2004 07:38pm | #1

   I'm doing a system now that is DIY pre-cut plywood, aluminum plates, and PEX run in the channels. It's known as an "above-subfloor sandwich system."  Straight forward so far, although pretty labor intensive.

   Main issue, I think, with the concrete floor would be that it probabaly is not insulated underneath, and w/o insulaiton, you'll be pouring alot of BTUs into the slab before you get much heat radiated into the room.  

   How much does it need to be leveled?  Is there head room for 2" of rigid and then the sandwich?  Or perhaps it would be easier, since the slab is already there, to place 2" rigid insulation just as if you were doing slab on grade, staple the PEX to the foam, and then pour Gypcrete.

   Have you done a heat loss analysis yet on this room?

2. 
   toolin | Jun 30, 2004 08:15pm | #2

   Done a couple like that,  definitely think about the insulation from the slab that was mentioned before or you'll be very unhappy.

   Used both the premade channels and homemade ones.  The premade ones I used where from Wirsbro and very expensive.  And they used 5/16" PEX to keep the total  thickness to a minimum.  With the 5/16 you have to be very careful with loop length etc..  The good news it went in real easy!!

   Homemade ones I did worked great. Ripped 3/4 plywood for the straight sections and made the curved ends on the bandsaw.  Used the Wirsbro plates (normally used  for staple up jobs.) on top of the strips. 

   You'll love the radiant!

1. 
   johnnyd | Jun 30, 2004 09:58pm | #3

   How did you fasten down the plates? I have about 400 to place.  I've heard both regular staples and shingle nails.  More precisely, the grooves are 3/4" wide, the width of the plate grooves is about 5/8".

   Best advice so far is to staple or shingle nail one side of the plate, with one side of the groove against the plywood groove edge.  Then press the PEX in, and finally fasten the other side of the plate so the groove (slight "omega" shape) grabs the PEX snuggly.

   Also, did you have any problems with or take measures to prevent noises during expansion of the PEX?  I've so far made the width of the groove wider in the looped areas (about 1 1/4") so the PEX has somewhere to go when it expands.

2. 
   Jim_McGee | Jun 30, 2004 10:01pm | #4

   Headroom's at a premium. Had to be because of the rooflines (it would take too long to explain). Bottom line, adding 2" insulation plus the 1 1/8" I've seen quoted for some infloor systems would be a problem. I've seen claims for one system that underfloor insulation isn't so much of an issue becuase of the metal reflectors they recess into the grooves. Are they full of it?

   The concrete floor is has waves and is out between 1/2" to 3/4" across the room. I was going to use poured floor leveler.

   JohnnyD asked if I've done a heat loss analysis. I wouldn't know where to start. I don't do this for a living but I'm pretty good with my hands and have worked construction in the past. Ask me to frame up a second floor and finish it off and I'm good to go. Ask me to size a heating system and I'm lost - which is why I'm asking for advice.

   Using pre-made underfloor radiant plates cut into plywood as a cost saver sounds like a good idea. But how do I determine how much tubing length I need in the room?

   I have a 1953 vintage boiler that I need to replace and the rest of the house (around 1400 sq ft total) is in-slab radiant, also 1953 vintage.

   Will I need to sledgehammer out the old concrete and dig down to install rigid foam to get enough r-factor for the system to work?

   Am I even asking the right questions? This is a new area for me.

   Thanks,

   Jim

1. 
   johnnyd | Jun 30, 2004 10:43pm | #5

   You are right on track with your questions...about where I was a year ago.  The purpose of a heat loss analysis is to make sure you don't overheat or under heat.  Has to do with what they call a "design day". That's the about the coldest day of the year in your locale.  For mine, it's -10* F, so with an indoor design temperature of 70* F, I've got to cover an 80* delta.  That's the starting point, and then you figure in the R values of floor, cieling, windows and doors, how many lineal feet of exterior, how many lineal feet of interior, floor coverings, etc, and then put it in some software, add a generous dose of real life experience, and come up up with how many btu per hour your structure will lose. Then you make sure that your heat source and distribution system is up to supplying the make up btus/hr with adequete acceleration and minimal short cycling. Has to do with water temperature, flow, loop and circuit length, zones, etc.

   Because I was lacking the real life part, I paid a consultant $200 to spec out mine.

   This will get you started:

   http://www.hydronicnetwork.net/hydronic/hea/

   Another place to search on is:

   http://forums.invision.net/index.cfm?CFApp=2

   or:

   http://www.radiantpanelassociation.org/i4a/pages/index.cfm?pageid=1

   Do some homework before you post, though, these guys are harder on newbies than the BT bunch!

   You'll hear alot of "rule of thumb" estimates, and they may well apply to your situation, but there are alot of expensive sob strories out there that started with an inaccurate rule of thumb heat loss estimate.

   Making your own plywood channels is kind of a fun DIY project, and could save you lots of $ on a premium system...but you do need to at least collaborate with a pro on the design and stickier installation chores IMHO.