# Heated Slab



## skipharper (Sep 11, 2011)

Under this definition what does "Hot Air Distribution System in contact with" the slab mean????? Zone should not have anything to do with the definition.


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## mark handler (Sep 11, 2011)

Are you asking what a heated slab is?

"Heated slab" means a floor slab in which an uninsulated heating element, uninsulated hydronic tubing or uninsulated hot air distribution system is in contact with the slab or placed within the slab or the subgrade.

Or are you asking what an "uninsulated hot air distribution system is"?

Which is self defining......?


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## Francis Vineyard (Sep 11, 2011)

Skip did you mean to ask what is it?  It is duct (piping) using force heated air installed similarly as the hydronic system.

IECC

HEATED SLAB. Slab-on grade construction in which the heating elements, hydronic tubing, or hot air distribution system is in contact with, or placed within or under, the slab.

IMC

AIR DISTRIBUTION SYSTEM. Any system of ducts, plenums and air-handling equipment that circulates air within a space or spaces and includes systems made up of one or more air-handling units.


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## skipharper (Sep 12, 2011)

HEATED SLAB. Slab-on-grade construction in which the heating elements, hydronic tubing, or hot air distribution system is in contact with, or placed within or under, the slab.

My thought is "HOT AIR DISTRIBUTION SYSTEM" means if a building has HVAC----so the hot air distribution system is in contact with the slab. AM I NUTS??????


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## Francis Vineyard (Sep 12, 2011)

Not nuts, just literal!

Commentary “The space above a heated slab is always conditioned (heated). The definition clarifies that certain slabs are the heating source and, as covered in the code, may require more insulation than unheated slabs. The installation of a radiant heat source in a space does not, in and of itself, qualify a slab as heated.”


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## Jim Harper (Sep 12, 2011)

I don't know the answer but I will take this opportunity to say hello brother Skip.


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## mark handler (Sep 12, 2011)

Skip

I still do not understand your question

Yes, Someone may create a heated slab with a HVAC system, I have never seen it, but it is possible.


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## skipharper (Sep 12, 2011)

Let me try it this way: Located in zone 4-new Lowes store with a concrete slab on grade. Is perimeter insullation required per 2009 IECC 502.2.6?


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## mtlogcabin (Sep 12, 2011)

http://www.chaleffandrogers.com/templates/sip2-air_floor_construction.html



> http://www.chaleffandrogers.com/templates/sip2-air_floor_construction.htmlIs perimeter insullation required per 2009 IECC 502.2.6?
> 
> http://www.chaleffandrogers.com/templates/sip2-air_floor_construction.html


http://www.chaleffandrogers.com/templates/sip2-air_floor_construction.htmlNo

http://www.chaleffandrogers.com/templates/sip2-air_floor_construction.htmlhttp://www.chaleffandrogers.com/templates/sip2-air_floor_construction.html

http://www.chaleffandrogers.com/templates/sip2-air_floor_construction.html' rel="external nofollow">3. CONSTRUCTION

Investigation of concrete block floors with respect to material and labor costs proved disheartening. Industrial metal roof decking provided the answer. In simplest form the system is built as follows. For a simple east/west rectangular plan with south glazing (a common enough plan form) the grade is first prepared for a concrete slab in the usual fashion. Rigid foam insulation is carefully laid down over the final layer of screeded sand. I most often use two-inch thick bead-board but polyisocyanurate foam board is recommended for those concerned with toxic combustion products. Most sources advise against placing any insulation under a direct gain slab, but because the delta-T is now substantially increased in this system, insulation is required in order to prevent large heat losses from occurring.








Fig. 1: Alternate manifold layout.
​Running east/west along the inside of the north frost wall install a vertical foam board and, as you approach this edge, excavate and turn down the horizontal foam boards at approximately 45 degrees to make a "vee" trench. This manifold runs continuously along the north frost wall and is proportioned like any proper supply duct tree. Along the south frost wall install the insulation in a like manner except the "vee" trench mixing duct need only be eight inches across the top. The steel decking is merely a form and thus is the cheapest grade I II inch type "B'. roof deck, 22 gage, painted finish. It is laid in two lengths lap-spliced in the middle allowing them to be spread tightly against and slightly into the vertical perimeter foam insulation and then locked with either tack welds, pop-rivets, or self-tapping duct screws. The concrete is poured over the decking to a thickness of about six inches to the bottom of the rib. The slab is reinforced with 6'.x 6"/10-10 temperature welded wire mesh and the necessary re-bars to span the manifolds. 1 1/2 inch flats on the bottom of the decking six inches on center bearing on 25 p.s.i. foam provides 900 pounds per square foot safe total loading. Sinuous decking would probably sink into the foam.

4. FINISH AND OPERATION

The slab can be finished with masonry (tile, stone, brick, terrazzo), or treated a la Wright with scored pattern, color, sealer with a wax finish. I have seen one of Wright's floors almost forty years later, and it looked brand new, like burnished leather. One would easily mistake it for some synthetic resilient flooring. My own efforts in this direction have been acceptable but less stunning than Wright's.

Another option is carpeting or wood flooring. This insulation will reduce the radiant delivery fraction and increase reliance on the convective component.

During the solar gain periods, as with any hybrid system, the auxiliary heat blower fan should remain OR. This switching can be performed manually or by automatic thermostatic sensors and solenoids. It is not necessary to operate the fan in order to recover the heat when needed because radiant delivery is usually sufficient. The auxiliary heating system can also be operated manually or by the customary thermostat.

5. VARIATIONS

Because the plenum floor is a distribution system, it can be coupled with any back-up system desired as long as that equipment produces hot air rather than hot water (although a fin-coil may be used here as a boiler adapter). I currently have in operation systems that are coupled to oil-fired furnaces, bottled gas units, "street" gas furnaces, wood/coal furnaces, air-source and water-source heat pumps, and even straight electric resistance furnaces. The system works well with either low temperature "trickle" feed sources or rapidly charging high temperature sources as with a Russian fireplace.







Fig. 2: Most common construction of plenum floor slab. (Larger image)
​On more than one system I have tapped a vertical supply duct into the supply manifold to service a second floor space. In two cases both "L" shaped and "V" shaped buildings have been constructed with the slab located off the grade at the second floor level. In these cases an insulated dropped ceiling was installed and supply registers were located to feed both up and down.


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## Architect1281 (Sep 12, 2011)

A Heated Slab is a Slab with Heat inside it - as in Radiant coil heat where the slab becomes the Radiator / Convector

a slab within a heated space, say in a foreced air system above is not a Heated slab it is a Slab

so defined like this

HEATED SLAB. Slab-on-grade construction in which the

heating elements, hydronic tubing, or hot air distribution system (used to be like transite duct for the older guys)

is in contact with, or placed within or under, the slab.

I can't believe I did that for a Sox Fan


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## mark handler (Sep 12, 2011)

Typically Lowes stores do not have heated slabs, based on the definitions given, do you have a heated slab?


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## skipharper (Sep 12, 2011)

It is obvious to me I have no idea what a heated slab is. It would be heated if the floor had hydronic tubing running all thru it, I understand that. I have no idea how (hot air distribution system is in contact with) could be possible unless it was the space above the slab. Thanks for all replies and sox are simply in a minor slump!!!


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## mjesse (Sep 12, 2011)

I'll try;

Slab on grade construction can be heated by a forced air furnace with ducts running below grade.

Furnace distributes warm air through under floor duct system.

Ducts are run prior to concrete pour, concrete is poured over ducts, ducts are "in contact" with slab

mj


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## skipharper (Sep 12, 2011)

So just so I get the total picture here we have a concrete slab on 4" of gravel base and the ductwork is turned up underground and the difussers dead end under the slab. And the return air.......


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## mtlogcabin (Sep 12, 2011)

Check out the link for a warm air heated slab on grade example

http://ottawaicf.com/air-heated-floors3.html

http://ottawaicf.com/legalett.html''>http://ottawaicf.com/legalett.html' rel="external nofollow">

http://ottawaicf.com/legalett.html


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## skipharper (Sep 13, 2011)

Thanks to everyone who helped me to understand this and the excellent links!! Great message board and don't worry about The Red Sox as this is a perfect time to slump, right before showtime!!!


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