3 RFH questions
1. Is using the foam staples to secure the pex to the XPS insulation under a slab as reliable as using wire mesh? Seems easier to use the staples but I have never done either one.
2. If using wire mesh, what about using chain link fencing instead of the mesh? At the local big box it is a bit cheaper.
3. If doing RFH in a basement and a DETACHED garage floor, where there is no conditioned space connecting the 2 buildings, would those systems run off different heat sources (water heaters)?
Thanks
Replies
Depending on the details of your concrete mix, the answer is yes. The wire is an easy way to attach tubing, but its purpose is to reinforce the slab. Fiber reinforced concrete mix seems to be the wave of the future over WW reinforced slabs. Need to work this out with folks doing the flatwork, and count on this in your budget.
Something is wrong here. Don't use chain link fence. Welded wire mesh should be available at a fraction of the cost.
Maybe. How far apart are the spaces? How are going to control the slabs? Does your heat source have enough capacity? You paln to use domestic water heaters for heat sources?
WM, baseed on the questions you asked, sounds like your in the (hopefully) very preliminary stages of learning about and/or planning these heated slabs. Keep digging.
Tim, thanks for the post. It will indeed be my first install, but I have read a lot about it. This forum has been a great place to bounce ideas read or heard elsewhere, including from the voices in my head.
They are pouring fiber reinforced concrete for the slab, and the concrete contractor said it does not require any steel mesh for reinforcement, with or without RFH. Perhaps he's mistaken, I am just taking his word for it.
Given that, those I have spoken with tell me the wire mesh is for tie-down purposes, and perhaps to help distribute heat evenly, which is why I inquired about the mesh vs the staples. That is also why I inquired about the fencing--it was a matter of curiosity more than anything. They wire mesh cost was about 15% more than the fence and it caught my eye that they both lay rather flat. Maybe the fence coating could degrade concrete or the pex?
I have asked several questions on this forum which have turned out to be doozies--I suppose everyone asks tham at the beginning, right? I'd rather pay the "stupid tax" here than from my wallet on the job.
1. Is using the foam staples to secure the pex to the XPS insulation under a slab as reliable as using wire mesh? Seems easier to use the staples but I have never done either one.
We used ONIX rubber (EPDM) tubing, not PEX. http://www.wattsradiant.com/professional/onix.asp PEX isn't the only option. OPINION only - I think wire mesh will do a better job of remaining stable when weighted by people walking on it, concrete, etc. It is primarily for crack control which is very important with radiant slabs (more movement due to thermal stress). Best bet - use wire mesh AND fibermesh both - this is an unbeatable combination for crack prevention - so is maximizing slab thickness.
2. If using wire mesh, what about using chain link fencing instead of the mesh? At the local big box it is a bit cheaper.
I really can't think of a reason NOT to do it but I wouldn't.
3. If doing RFH in a basement and a DETACHED garage floor, where there is no conditioned space connecting the 2 buildings, would those systems run off different heat sources (water heaters)?
No reason to do that - we have a radiant loop off the boiler doing both house space and garage workshop - the line to the garage workshop runs under an open breezeway - but it is extremely well insulated.
Protection - in areas where there was a (slight) potential for nail penetration from walls erected later I cut sections of 1" x 1" x 8" steel angle and taped them over the tubing with electrical tape to deflect nails. No problems.
Jeff
Edited 1/8/2008 10:35 pm ET by Jeff_Clarke
Jeff, thanks for the reply, very useful.
Mine would run under a breezeway as well between house and garage--how did you insulate it? I was considering using insulation-wrapped PVC as an conduit between the buildings, but haven't looked into it at all yet.
And do you have an antifreeze in yours since it goes between building?
We ran through Carlon (electrical conduit) - 2" diameter and insulation with XPS board - 6" total thickness all around. Buried down 2 1/2 - 3 feet with insulation there's no need for glycol, which is corrosive and toxic, in our climate. The RH manifold is in the workshop where it will be encased in insulation and within a shop cabinet - right now we just watch the heat (set at 44 degrees until the space is in active use).
Jeff
I'll have about a 25-30 foot run form the heat source/interior termination to the garage. I'm not visualizing the insulation of the conduit with foam board--how does that work? Do you make a long narrow box of it in a trench and run the conduit in the trench?
Did you run the full loop in the conduit from the boiler then on the foam in the garage/shop then back through the same conduit on the return? That would be about a single 300' run for me, whcih seems a bit long. The runs inside are 2 x about 260 feet. If they are on different zones, does it matter that they have different length runs?
I will discuss this with the HVAC contractor, who will eventually hook up the system to the heat source. I want to have some knowledge in my back pocket when I discuss it with him--probably just enough to make myself dangerous, but I think many heads are better than 1.
FWIW, they make heat pipe with insulation just for these kind of applications. Used for central heat systems that supply individual building.Probably not worth trying to source it for this small job unless one of your local suppliers normally stocks it.And you might want to look at using an upsize common pipe and then a mini manford at the other end..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Good tip Bill, thanks.
Yes - the supply and return piping (Onix) each has its own 2" conduit and the whole thing is 'boxed' with insulation. For bends we used full 10' lengths of conduit and bent them into the necessary very-very-long sweep bends to ease transitions.
Jeff
Wire mesh does not appreciably affect the distribution/transmission of the heat. Concrete is quite conductive, and in a 4" thick slab (or thicker), the tiny wire mesh is insignificant in comparison. IF the concrete is otherwise reinforced, staple the tubing directly to the rigid foam insulation.
westmich
I used the staples even without the gun,, I just pushed them in by hand and then poured the concrete on top .. very easy!
Just curious, did you use a water heater?
al
(G)
eleft
Sorry I tried to answer you yesterday but for some reason couldn't?
Yes I used an electric water heater with another electric water heater as back up for those really cold days we get up here in Babe the Blue Ox territory..
that's for 5500 sq.ft. house..
I am pretty sure the galvanizing on the fence would degrade the concrete. Seems a friend who likes to play with concrete told me that.
Just my $.02:
1. There has been some discussion on either this forum or maybe The Wall over at Heatinghelp.com about thermal effect of stapling to the foam. My remembrance is that someone looked up some thermal models which showed that a bit more heat was lost by putting the tube down at the bottom of the slab vs. in the middle, as you would hopefully get by using the mesh.
However, given that the mesh quite often ends up at the bottom of the slab -- most concrete finishers won't put too much effort into making sure it gets pulled up as they pour -- doesn't seem like that would be a real concern.
In my garage, I decided to tie to the mesh. I propped the mesh up somewhat before the pour, to at least make it easier to pull it up. Don't think you can really get it into final position unless you've got it well supported on rebar grid, as it's going to get walked on, & finishers probably wouldn't appreciate having to work on top of it.
Even with me & my father helping my finisher & his son during the pour, I know there are spots where the mesh didn't get pulled up.
2. I'm thinking the chain link fence probably wouldn't be as strong. On the one hand I think it's a heavier wire, but the advantage of steel in the concrete is it's tensile strength. Since the adjacent rows of the fence are separate, and the individual wires are bent, I think there would be too much flex in either direction for it to be much help. Don't think the risk would be worth the savings if it's a fairly important floor, which is somewhat implied if you're putting radiant heat in it.
I used mesh, and put 3 continuous rows of 1/2" rebar around the perimeter of my 24x36' slab. Also put a grid at the front where vehicles drive in. Would have used more, but the reasonably priced source didn't have enough. 2-1/2 years so far without a crack - didn't put any relief cuts in.
By far the biggest factor as far as stability, cracking, etc. is proper substrate material, compaction & drainage.
3. This would probably just be a matter of looking at the heating load reqirements of the detached garage, comparing that to the capacity of the house's heating plant, and looking at the costs of piping heat to the garage. There are others who can probably advise you better on what heat sources to use. I'd be careful about oversizing the house heating system just to accommodate the garage, though.
Don
I've never used staples to hold down the pex, but i'm not sure it'll hold. Pex tubing isn't as soft as one might think. We use welded wire mesh (flat sheets not rolls, purchased from our local concrete product supplier for a fraction of what the "big box" sells it for) the with zip ties. The mesh also allows for easier instalation because you don't have to think very hard about layout, it's like working on a sheet of graph paper. We layout our tubing in a circular pattern as opposed to a zig zag Pattern (think electric stovetop element) this offers better heat distribution throughout the slab.
Tim, Don, Nate, thanks for the replies.
I plan to use the wire mesh, maybe I can get it from the concrete supplier. I saw my neighbor's installed before the pour and he used zip ties and mesh but didn't have it pulled up near the surface at all--they just let it stay on the foam boards. Probly be nice to have it up another inch or so--I'll ask them to do their best at the pour to do so, but won't get to crazy about it if it won't make the system that much better.
I have several weeks before the pour, plenty of time to get things in order. Thanks for all your ideas.
I have only done two installs of radiant tubing so I am no expert. That said the companies I worked with on the install required 6-6-10-10 mesh to tie the tubing to . It was not intended as reinforcement for the slab. It's sole purpose was to keep the tubing in place at the Bottom of the slab. Engineers required #4 bar @ 2' o.c. for slab reinforcing. I also would say that there is something wrong with the pricing of fencing versus the mesh , Here mesh is much less expensive.
They can't get your Goat if you don't tell them where it is hidden.
DiverseNate,
Ahh you should try it!
I mean the foam needs to be there, it's what prevents much of the heat energy from being absorbed by the ground. and the stapels do hold!
Remarkable since they are just shoved into foam. I'll agree that wrestling with Wirsbo or pex is like trying to tame a snake but the staples do the taning for you.. try them I think you will like them.
I am preparing to build a pole barn shop with radiant heat in the floor, and have done a lot of research. In response to your questions 2 & 3, I would agree that chain link fence is not a good way to go, and as a previous response was stated on how to insulate an underground loop connection.
As far as staples into xps, I was going to go that route, until I found Crete-Heat. From what I have found, it costs more, but there are labor savings in the installation. I agree with frenchy that it is important to have proper insulation, and don't forget about perimeter insulation as well.
And make sure you get a proper heat load calculation.
Just my .02
Mitch
Thanks for the tips. Regarding a heat load calc, I am just putting RFH in the basement as supplemental heat, primarily for making the exposed concrete floor more cozy for the family. There will be forced air registers in the basement as well. With a well insulated slab and basement walls, who knows how often we'll actually be uncomfy down there. May not use the RFH system much at all.
In the garage, we just want to take the chill off when the kids use it for playing basketball and floor hockey in the winter. Not looking for exact or complete heating.
Still need a heat load calc?
I used the foam staples to do a 1200 sq ft slab. First time install, 2 people, me and my wife, five loops under 4 hours start to finish including layout. It was very easy to do and the stand up stapler was nice to use. Seemed to me that it would be far faster than tying to the mesh.
Tom, staples look easy to me as well. Did your install require rebar for structural strength? Some are saying that wire mesh and/or rebar are suggested for RFH installs.
I didn't use it. I used fiber reinforced concrete. Is that right??? I don't know. It's been in place for a couple years and no problems. No cracks anywhere other than where they are supposed to be.
Slab at my other house has wire mesh and no fiber and had cracks in under two years.
I heard arguments both ways. Pretty sure either will work well enough for a basement floor.
fiber reinfrocement doesn't do very much to add to the tensile strenth of concrete, and it certainly does not replace welded wire mesh. (Read Working with Concrete, Rick Arnold, Taunton Press.) What it does do, is add to the plasticity of the mix, and it reduces cracking in the flatwork AS the concrete cures. However, welded wire mesh isn't usually required in radiant floor instalations because areas where radiant heat is installed, usually are insulated , and therefore protected from freeze thaw cycles.(although not always, in heated driveways and agricultural application.)
Like I said, I'm not sayin mine in right, but it appears to be working well. I did it that way on the advise of the local foundation pros.
Tom
I did a little over 600 feet by myself with out the stapler, just pushing the stapels into the foam. I think I had about an hour (including layout) It might have been longer But it sure went fast and easy..