The new shop (pole building) is nearly shelled and the builders will be packing up their tools this week. Now I get to be busy with preping the floor installation.
I want to install radiant heat, but getting good information has been difficult about the floor preperation.
Any wreckers done this recently?
I'm looking at $268 for 1000' of pex 1/2"
2" Extruded poly styryene foam for ground cover (what should this cost)
I was told to use 25psi, anyone know what the stuff at Homedepot is?
2" of gravel UNDER the foam
4" of concrete poured over the pex and the wire mesh which holds down the pex.
A Womack wrote: > The new shop (pole building) is nearly shelled and the builders will be > packing up their tools this week. Now I get to be busy with preping the > floor installation. >
Time to get a good heating contractor involved.
If you don't want one to do the job, that's OK, then hire them as a consultant.
When you end up pouring concrete over your design, you only get one chance to do it right.
One wants $7000 for materials and install + the concrete! They bid $1500 for foam, pex, and mesh and I pick it up
Pex is $268 delivered on EBAY with a profit for the seller Foam I am still priving but I have found the local wholesaler and they don't recommend buying from the floor guys Mesh or Rebar, i understand I can get rebar and tie it myself for less than the mesh.
I have to find out how deep the pex is supposed to be now.
Second issue is contractor number 2 does not return calls.
i have had experience with differant installations. myself i put the pex in the sand under the concrete about
2" deep with foam only around the outside of the slab about 20" deep. once the sand is heeted up it's a big thermal storage basin. i recommend not more than 250' of pex on a loop or zone. keep your beginning hot run on the outside run in about 20" from edge of slab with 12-16 " spacing on the loops. keep th hottest part of your runs to the outter working inwards for the return to manifold. i know of many places here set up like this and it works well. of course it only gets to around 30 below here at times. i just use a garden hoe to cu a trench in the sand lay in the pex and cover. works best with 2 people, 1 to hold the pex in place while the other packs in the sand as you go. ross
we use sand, then foam, then tubes. i think you would be crazy to skip the foam under the slab as another poster suggested. unless you own your own hydro plant or oil well or something. the tubes are stapled to the foam. menards here in mn sells everything you need, including staples. get 300 foot rolls, as that is the maximum loop length you are allowed. 1000' foot rolls are not managable without an unreeling gizmo. do you have a tubing layout plan? most of the time, the tubes are 12" on center, 6" oc on the perimeter. with a sheet of graph paper, you could get your own layout figured out. i built a small house this winter, 24 x 32, and it took 3 300' loops. good luck.
just because you think i'm crazy do'snt mean i'm not. but i still think i'm right in puttig the pex in the sand.
1) heat tends to go up not down
2) ground holds it's own thermo temp
3) sometimes cement cracks,what happens to the pex imbedded in the cement?
4) the sand helps defuse the heat, giving more even temp on slab. i did an install in a basement under a new house. the guy put foam under the slab. had one night of freezing temps before he turned the water loose into the pex, when he did it froze before it made it all the way through. the only places it did not freeze the slab was where there was pads for support posts spaced down the cntr with no foam under pads. go figure. he spent $1000. to rent heat blankets to warm up the floor. and yes i do have my own hydro plant burning wood. about 12 cord a winter to heat my house shop, dry kiln and domestic hot water. ross
I just did my own 2200 SqFt house, and followed this plan. In addition I did the garage and covered porch. In all there's 6 zones, and something like 10 coils.
One think I would suggest is when you have the pipes that come up though the concrete, feed the pex through 1" electric conduit 90 degree elbows. This keeps the pipe from kinking or angling up during the pour. I purchased some of the metal channels used in commercial electrical applications to support the manifolds during the pour (mine are out in the concrete field. Drive it into the dirt plum before pouring and set channel in the concrete. With a little rigging, I was able to put about 30# of air in the pipes and that way knew if they were damaged during the pour.
Wirsbo has compression splices that were on hand "just in case" the pipe was nicked during the pour...thank goodness we didn't need it.
I was told that the bubble sheet wasn't effective as the foam. DAGS and you'll find pros and cons...I choose to use Owens Corning Foamular250. They have 2 grades of pink 2" foam, one rated for under slab one is not. In addition, I put 6 mil plastic under the foam, to keep ground moisture from migrating up into basement floor. Maybe overkill...but for a few bucks...I wanted a dry basement, and this is just one more element.
You can buy molded foam panels made to insulate and to hold the pex in channels. I've seen some that have a foil layer on top to help reflect the heat. I'm certainly not an expert on them, but they are worth looking into for the best job.
As for the foam, you can usually buy board stock, expanded foam, cheaper than extruded. Check out the local foam molders near you and buy direct. There are companies in every state so you should be able to find one and save a bundle.
My research suggests that the need for insulation under the slab is dependent on the presence of water in the soil under the slab and the level of any water table. Water will conduct heat rapidly. Dry clay will act as a thermal mass and while heat will leak out, like you say, heat prefers to rise. The normal temperature of ground below the atmosphere affected zone is ~53F. not insulating under the slab will mean that the slab in a covered building is unlikely to go below ~40F even after an extended period of no heat, but use caution YMMV. If the heat source is costly and used constantly then insulation may be indicated, but I would submit that 1" or
1.5" would be sufficient. If the heat source is DIY wood then cost may not be a major factor and the added thermal mass of the under slab clay may be more worthwhile, since with wood heat, storage is a bigger consideration since the fire will not likely be continuous. Not insulating the slab will also tend to keep the floor cool in the summer.
In any case, heat is far more likely to leak out of the edge of the slab and I would suggest that is where insulation should/must be placed. As you suggest 2" vertical rigid board 24" deep and extending to the top of the slab. Allow the (2x6 frame) wall to hang 2" over the foundation to cover the top of the foam board. I think that the effectiveness of this board can be doubled by the addition of another 1" foam board 24" wide buried at 45 degrees which will prevent the frost from penetrating next to the slab.
I have no comment on burying the piping in sand under the slab beyond that it is an interesting idea. I am inclined to think that the heat conduction will be better with the tubes in the slab but YMMV.
IMPORTANT, If the tubes are poured in the slab they should be filled with water before the concrete is poured in order to stop them from floating to the surface of the concrete.
While I don't agree with the thought that water will keep the pipes submerged, it really isn't an issue IF the pipe is stapled adequately to the foam. Adequately would depend on your concrete guy...is it going to be poured with a pump truck, slid down a half pipe, skid steer over the edge etc. My thought is staples are cheep...don't skimp here. The more the better.
In central Iowa, 2 inch Foamular250 (owens corning at menards can be had for $19/sheet on sale...around $21 not.
Something you might also consider is putting foam inside your footings so it meets the foam under the concrete. That will keep the cold from radiating into the concrete floor from the sides.
We installed radiant heat in our new house last year. My memory is that the contractor recommended re-bar rather than wire mesh, not for the additional strength of the concrete, but because it allowed him to tie the PEX tubing to the bar at a fixed height, preventing it from floating anywhere in the concrete mix. He used a thermal reflecting blanket as a moisture barrier as well as to minimize heat loss.
With respect, If the outside of the slab and footings are not properly insulated, then insulating the inside of the footing does not insulate the edge of the slab from the coldest exposure. If the outside of the slab and footings are properly insulated (to an effective depth) then the effect of insulating the inside of the footing will be minimal but will do little harm, it should certainly be done if there is water under the slab or footing.
By far the most important location to insulate properly is the outside of the slab. This will also help to prevent frost from penetrating under the slab in the event that there are periods of no heating in the slab.
Why is this? I have been unable to find any empiracal evidence of a university conducting tests, or a trade group.
I'm considering embedding a fair number of 1-wire sensors to make some real-world data available. I might even try one section of wall with the radiant barrier and the next one with normal insulation to put that controversy to rest.
I can swap it back next year when it doesn't work as well as they claim it will.
I do not have a cite beyond common sense. IMHO heat transmission/loss rate is propotional to the delta (difference between the adjoining substances) and the thermal conductivity of the interface. Heat is easily conducted laterally through concrete and a concrete > air interface will also conduct heat readily due to air circulation. Sinilarly heat can readily flow from the concrete to frozen ground (at a slightly reduced rate) due to the delta but also at a somewhat further lower rate due to the lack of circulation. When any insulation or thermal break is placed between the edge of the slab and the adjoining frozen ground it significantly reduces the effectivness of the thermal interface and slows the heat transmission. IME the perimeter insulation, combined with sunlight reflected from the wall, will significantly reduce the amount of freezing of the soil next to the footing and this unfrozen ground (depending on density and moisture) also acts as insulation for the slab. The thin sheet of insulation @ 45 degrees is intended to maximize this frost free zone next to (and under) the footing.
If a grade beam or minimum slab edge thickening is used instead of a proper frost wall then reducing the penetration of frost under the slab is vital to the life of the slab as the frost can cause significant slab stress and movement in addition to increased heat loss..
This will be a good project and you can do a paper that will impress the accademics and may even get you cited here. It will be hard to account for all the variables like soil desities, water content and circulation and sun exposure but we here can just use those to argue and critisize your findings. Quantified data for heat loss downward from insulated and uninsulated slabs would be more interesting to me but are also subject to the same variables of soil density, conductivity and moisture and circulation. These measurements will also be affected by the adjoining areas with different amounts of insulation so we will be able to question your methodology there as well. I suspect that this work has already been done by somebody with a significant grant or budget (of OPM) and perhaps it would be a better use of your interest and efforts to research the existing knowledge base and report back here with cites, or even better, weblinks.
The bottom line is that this really is not rocket science, and you should not lose sight of the need to properly do all the other stuff like underslab gravel, compaction, underslab poly, concrete quality and placing and finishing as well as site grading and drainage. Slab heat is really nice but its cost effectiveness also depends on the construction of the building and the choice of boiler and fuel. A simple small water heater (with suitable controls) can be used for primary (expensive) or backup but these systems really shine when combined with a ready source of cheap fuel like wood waste.
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