infloor heat in sand?

Tundra

The system should work for you, but... This is a huge mass to warm up. You may want to start warming the slab in July so it is ready by winter. (A silght exageration.)I don't know what part of the country you're in but you may want to consider additional insulation.

HAROLDS

INFLOOR HEAT IN SAND?

WE ARE LOOKING AT A JOB AND THE OWNER WANTS INFLOOR HEAT THE HOME WILL BE SLAB ON GRADE, THE PLAN IS TO PLACE 2" RIGID INSULATION, THEN OUR TUBEING, THEN 6" OF SAND, THEN 6" OF CONCRETE. HAS ANY ONE DONE IT THIS WAY BEFORE? WILL IT WORK? WHY US THE SAND? ANY INFO WOULD HELP

Constantin

No, it won't work well.

The sand will do nothing but a really good job of insulating the tubing. Instead, run the tubing through the concrete. 4" of concrete is usually good enough for residential construction, use more if you wish, but it will slow down system response (this could be a good or a bad thing, depending on the application).

Here is what I did in a cold climate in my own home with the layers described from top to bottom:

• 4" of concrete
  
• &frac12" PEX tubing on 12" centers, 250' loops
  
• wire mesh, reinforced in re-entrant corners with #4-60 rebar
  
• 6 mil of Vapor Barrier
  
• 2" XPS (Dowfoam (?)) - I may have the this and the above switched.
  
• 12" of gravel (because of drainage, radon, clay soil)

Works like a charm. You can read more about this subject at the RPA web-site, as well as Building Science Corporation. The best place for the sand may be as an insulator underneath the foam/vapor barrier.

Lastly, you may want to lay off on using the caps-lock when you type your messages, as that's interpreted as SHOUTING in the online world. Cheers!

thp_8

Big Heat Sink (Thermal Storage)

If it's about a 30 yard concrete pore.
You would get roughly between the sand and concrete a 180,000 pound thermal storage unit. Wish I had that in my basement.

Alex Giacomuzzi

Yes, Yes, Leveling & Drainage

Yes ---- it has been done this way. It is certainly not the preferred method though.

Yes -----it will work. It it not as effective or as responsive of a design. Putting the tubing into the slab makes a much better radiant emitter than barrying it in the sand below the slab. As the sand dries out, (which it will in short order with heat on it) it becomes more of an insulator rather than a good conductor. The actual responsiveness of this huge mass (sand and concrete) would almost be snail like.

Regarding your last question..... the reason to use sand
It would serve a great purpose of both providing drainage if required and some degree of insulation but mainly a great leveling bed BELOW, not above the 2" of insulation.

The home owner has almost all the necessary pieces, just in the slightly wrong order.........

Regards Alex

Gordy

Hard to control;

Thinking about control strategy here. The thermal swings would be hard to control. Heat when you don't need it. Waiting for it when you do need it. Good ant farm.

jerry scharf_3

seems like a bad idea

Harold

(It's considered more polite to not have the whole message in caps, it's considered shouting hee.)

Some people say it will work, but I think it would work badly.

The problem with sand is that it is a fair insulator and that it has poor heating coupling to the pipe (it's the lack of contact surface area between the grains of sand.) Just because you have the heat in the pipes does not mean it will make into the floor. Even when the heat does make it into the floor, it has to penetrate all the way up. If you assume you put it 1" down into the sand, here is a SWAG of the covering R value. 1" of dry sand for R2, 6" of concrete for R6 and the floor covering for R1. That's R9 between the point in the floor and the sand by the pipe. This is going to make it very hard to get enough heat from the tubing to the room to meet the heating demand, even with very hot water. If you put in in the middle of the slab, the coupling is much much better and you only have R4 on top.

Others have mentioned the thermal mass of the floor, and you will need to take that into account with your controls. The lower in the slab the tube lies, the more the 'flywheel" effect. Don't even think about nighttime setback with a floor like this.

As for why use the sand: if the site or similar ones have experienced slab cracking, the sand will distribute any differential earth motion. This helps confine the cracks to the score joints. I did my garage slab just that way.

jerry

JohnWood1

Commercial App?????????

This is a common application in commercial applications. Works very well where you have overhead doors up and down all the time as the mass of the concrete and sand will give a great thermal mass to work from. Just use the lowest temps you can for the install. In fact a reset would be in order.

Residential? maybe...... mabye not. One great app for both commercial and residential is to use this system with and electric boiler and allow the util to control for off peak power. Saves a bundle in heating costs and works bedause of the mass. Multiple millions of btuz stored in that thar floor!

LKE

insulator?

Good insulators have lots of air spaces, the more the merrier.The spaces between the grains of sand is equal to one third the total volume of the sand. If their is water or something else in that space like cement paste it conducts, but dry sand is considered a very poor conductor.Jerry and some others have advised you well, this would be a very disappointing installation. The ancients seemed to be aware of this as it has been reported that Pollio Vitruvius the Roman architect and engineer who wrote the first engineering manual made reference to this in his work.