Replies

1. 
   Mongo | Sep 06, 2002 06:30am | #1

   I've done several staple-ups.

   Either half or five-eighths inch PEX w O2 barrier...usually Wirsbo tubing...two runs per 16" or 19.2" bay.

   Al plates? Depends on the load requirements. The only time I've needed them was for a 4-season sunroom. Lots of glazing, so the plates were used 4' in from the exterior walls. You can either buy them commercially or buy the flat stock and bend your own. Realize it's not common Al coil stock. It's a different animal. More malleable, designed for the thermal cycling of a RFH setup.

   Under the tubing and between the joists I friction-fit half-inch foil-faced polyisocyanate RFBI. In the basement (first floor heating) I add another layer of R19 FG batts under the polyiso. In the other floor systems (second, third floors, etc) I'll either blow in cells (thermal overkill but helps with sound), use more FG (R11 to compliment the polyiso), or just use thicker polyiso with no cells or FG. It's unrelated to the RFH, but typically I insulate all framing cavities in the structure w cells for sound attenuation, which helps the thermal characteristics of the building as well. Regardless, for best success, always use the foil-faced polyiso...with thickness (R7.2 per inch) dependent on required R-value...under the tubing. Add more R-value as it is needed, where it is needed. Easiest way to add extra R is to use thicker polyiso, second easiest is FG, third is to blow in cells.

   In general, try to have three times the r-value UNDER the tubing (polyiso and FG) that you have over it (subfloor/underlay/finish floor assembly). That will persuade the generated BTUs to travel upward through the floor assembly to heat the intended living space and prevent thermal overload in a room caused by the room being heated by both radiant floor and radiant ceiling.

   Careful with how tight you pull your loops. You can end up with friction noises as the tubing expands in the first few heating cycles of the season. Sometimes it helps to stuff waste FG, or roll up a small piece of cardboard into a sleeve, and use the FG or cardboard to line the hole in the floor joist that the tubing passes through. I've never had a noise problem, but that's a trick I know that's been used to quiet noisy systems.

   Follow the installation guidelines on using Al plates if you go that route. If not properly secured, they can click and pop as they expand and contract, too. Again, the Al stock designed for RFH setups is less problematic.

   Circulation temps are traditionally higher with a staple up...though most of mine run 115-120F. Not a big problem.

   Call Wirsbo (8003214739) and ask them to send you a copy of their Complete Design Assistance Manual.

   Edit: Wanted to add, for thermal comparison purposes, that I'm in CT.

   
   

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   Edited 9/6/2002 9:00:23 AM ET by Mongo

1. 
   DavidThomas | Sep 06, 2002 08:59am | #2

   That's all great info from Mongo. Up here (design temp = - 40F and that definitely happens sometimes), staple-up can be a problem. Without fins, it can be marginal in even the tightest, best insulated house. Most houses up here are marginal even with the factory Al fins. But in a milder climate? Yes, staple-up is viable. Especially under tile, like in a bathroom. Under carpet with pad, you will of course get less BTU/square foot because of all the insulation between the space to be heated and the hot joist bay below.

   The insulation underneath is important so the heat goes where you want. If the downstairs is hot enough, but the upstairs is calling for heat, you don't want the downstairs overheated by a radiant ceiling.

   David Thomas   Overlooking Cook Inlet in Kenai, Alaska

1. 
   royboy | Sep 08, 2002 04:40am | #3

   thanks, you guys, for your thoughts! I called Wirsbo and ordered their design manual.

   I'm in extreme northern WI and we too design for -40 temps (despite the fact that it's currently about 80 at 9pm - yikes!). So I'm gathering that the recommendation from you, David, would be definitely for the aluminum transfer plates.

   And I'm thinking that instead of my standard rule of thumb sizing that I've done for slab installations that I'll get a little more rigorous here and do a heat loss calculation. Either of you - or anyone else - have any suggestions for a simple heat loss calc tool? If a cyber tool - something compatible with a Mac would be best for me ...

1. 
   brucepirger | Sep 08, 2002 01:36pm | #4

   I need to think about this soon as well....al plates or not for staple up.  I think there is a very big differences with the plates.  The thermal conduction from the tubing to the air...and then to the floor is much lower without the plates.  I have seen this analyzed before....most likely in the Wirsbo design book...maybe in Seigenthaler's book.  But anyways, it does seem the heat tranfers from tube to plate to floor would be WAY higher than from tube to floor directly.  It's all about surface area contact...and metal is so much better than air.

   I like the friction fit foilfaced polyiso idea.  I will install my staple up I think once we have moved in...fiberglass is NOT an option.  I'm installing my R-38 in the trusses now.....I HATE FIBERGLASS!  Anyone use the foiled bubble wrap? 

   My understanding is that the al plates are not cheap...but I'd think maybe you can use just a single run per joist bay, 16" OC, with the plates.  So maybe it's not so bad...less tubing...fewer loops.

   WetHeadWarrior...any comments on this staple up application? 

   I know a guy that made his own plates from thin al plates discarded from a local newspaper printing company.  Set up some kind of a press and just cranked them out...

2. 
   DavidThomas | Sep 09, 2002 04:58am | #5

   Certainly Al fins versus no fins. But in N. WI, a poured gypcrete floor would the completely sure thing. I think you are right to do a heat loss calc to check the feasibility of staple-up using heat fins. And compare to Wirsbro's calcs on heat output from differect installations.

   My simplest heat loss rule of thumb is that a typically constructed modern house loses 0.3 BTU/hour/square foot of floor space/Degree F temp diff. FG batting in 2x4 walls, passes code but not especially careful construction, etc. (two-stories on a 1,000 sq ft foundation = 2000 feet. And for a really well insulated, very tight house without a huge amount of glazing, use a factor of 0.1. In between those endpoints, estimate where the house in question will fall.

   I've made site-built heat fins by bending aluminium flashing over a #4 rebar. Not as nice as teh factory ones but they hung nicely from the tubing and were way cheaper.

   David Thomas   Overlooking Cook Inlet in Kenai, Alaska

1. 
   brucepirger | Sep 09, 2002 05:20am | #6

   Hey Dave, How exactly did you bend the metal over the rebar?  The factory sheets, which I have never seen, kinda "pop" on over the tubing, right?  Almost like a snap fit?  Or are they looser?

   Did you use a press or brake or something to make your own?  I'll explore the idea...but most likely won't have the time in the end to make my own.

   Thanks for the info!

2. 
   DavidThomas | Sep 09, 2002 07:33am | #7

   Just with leather gloves on. Duct taped the 1/2" rebar to a sawhorse. Took each piece, about 10" x 7" and laid it over the rebar, longways. Folded it over till the two halves touched. And then pinched it a little below the rebar to over-bend it. So it would be a snug fit.

   Took maybe 5 or 8 seconds to bend each one. Cutting took a while till, after two dozen, I thought, "screw it with the tin snips" and ran the whole roll of flashing over the table saw. One circumferential cut and two or three longitudinal cuts. Eye, ear, and hand protection are essential as is a firm and steady grip. Two rolls of flashing, 14" x 50' covered the tubing for a 500 sq ft garage loft.

   David Thomas   Overlooking Cook Inlet in Kenai, Alaska

3. 
   Mongo | Sep 09, 2002 04:44pm | #8

   Radiantec is one of the more DIY friendly companies around. I thought that a few years ago I saw a schematic of a "rebar or conduit brake" that David described for bending your own plates. Just ensure that your homemade plates don't have sharp edges. Expansion/contraction cycles could slowly scape away at the walls of the tubing. Not likely, but I have heard stories of it happening.

4. 
   brucepirger | Sep 09, 2002 08:59pm | #9

   Thanks David and Mongo. That sounds like a quick and easy idea.

   I don't remember for sure, but it seems like I recall something like $600-$800 for aluminum plates for my 1100 sq.ft second floor.

   Yep, what a mess a sharp edge can make! Thanks!