Hot Water In-floor Heating

It all depends on the relative thermal conductivity of the two materials.

Off hand, I'd say no. You'll keep all the heat in the pex, and less will come to the surface.

Remember the heat is radiated and conducted in all directions. Out is the important one.

Up is the other one.

Small particles with lots of contact area conducts heat.

If the water was slowed down, so as to allow more conductivity, the temperature of the whole mass would be the same, I'm not sure. I know that gipp crete is mostly pummace, and does make more surface area to conduct from, but after seeing the bid on bringing in a "gip crete" crew, and the mess of it all, the cost of good sand, plus the ability for us to "install" the tubing and the sand ourselves, was quite dramatic. The weight of the "slab" was about the same I think.

Actually dry sand does have approximately the same thermal conductivity as light weight concrete....now as far as density and mass, not...This might effect the cycling time...Now clay might work...Thermal Mass...

http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html

Installing sand seems cleaner and faster, and if the thermal conductivity is about the same, and the weight of the slab is about the same, I'm getting close to doing it.(one less subcontract crew to pay) The final product IS WARM FRIENDLY FLOORS.

Always good to be an educated consumer

Safe link to Extreme How To, click HERE

Can you get to the underside?

And on another note , don't have to actually use concrete

Most of these light weight concretes used in that application are formulated to have a high thermal conduction. Not all light weight concretes are recommended for this application. Those for this application will have a higher thermal conduction then you will get with just sand. Unless you float the sand in between the joints wet like concrete it will settle. May even settle some even if you do that.Being loose sand it would also find away to migrate through the sub floor unless it's very well sealed. Then you will have an air gap. . Which would be an insulator. You also have to look at the weight of the sand over what this concrete would weigh. Don't want to over load the floor.

"Lightweight Concrete"-LWC - Pumped into the radiator Piping grid remains where poured. LWC cover over Hot water piping can be 1/2" .Heat transfer will be good.

Silica Sand is very heavy and will move all over.You end up carrying a huge burden of loose sand and heat conductivity through 2" cover loose Silica sand will be poor.

mm

My first exposure to heated floors was more than forty years ago, in a single story, cement block house built on top of a cement slab in 1949. The owner strategically plumbed hundreds of feet of copper pipe, creating zones in the process. i was sold on the concept the instant I walked on the linoleum tile floor with my shoes off.

Many years later, I watched heating mechanics on "This Old House" hose cement onto a basement floor, only the heat conducting pipe was flexible thin walled plastic. A thick layer of insulating foam had been placed against the earthen floor first.

You may have a substantial advantage over those prior efforts in that you are preparing to do the same thing on an existing wood frame structure.

Judging from what my son-in-law just did, yours may be old technology.

He attacked the problem from downstairs and the only tools needed were a staple gun and a step ladder!

PVC tubing is attached to the sub-flooring from downstairs, with the tube running back and forth between two joists before transiting one joist via a small hole. It then turns 90 degrees and repeats the process.

Afterwards, 14-inch wide thermal barriers are stapled in place over the pipes. Done!

A subsequent airing of This Old House showed us different method: a 6 foot (?) length of extruded strip with snap-in-place slots that allow the tubing to be simply snapped into place.

I plan on using one these newer methods to heat the floor on a modular prebuilt 20 x 20 shop building. I will install the plumbing on top of the existing flooring. A pattern of parallel strips on wood will elevate the new floor.

Yes, I'll loose about 1.5 inches in ceiling height but that's OK. You may want to consider this alternative if you do not have access to the floor from below the house.

These methods promise to be a lot less expensive in materials and labor and are easy enough to perform for the average homeowner who can to do it himself. And, the structure will not be burdoned with the weight and other problems associated with a poured cement floor.

Over time baseboard heaters darken the wall above them. The coils must be cleaned periodically to maintain a modicum of efficiency. The walls repainted

Forced air heating systems have the advantage of doubling as air conditioning ducts provided that they are sized for cold air. But, they are noisy as Hell, dry the air and I refuse to have another home with that system.

These new systems offer uniform heating throughout the home, are quiet and maintenance free. The ease with which they can be zoned and managed with servo operated valves promise lower fuel bills.

I'm only concerned a little with the consequence of carpeting, not in the shop but when I do my home.

Good luck

Laughing Jaguar

I installed my radiant floor heating from below like you but I used r-19 foil backed fiberglass insulation foil side up leaving the pex tubing in a 3 inch space. Works great! carpeting has shown no difference in heating. One note to pass on. Do NOT use a wax ring on your toilet! (I had a real mess on my hands the first month we had the system on). Good luck

I installed an "overlay" underfloor heating system about 2 years ago using a system that you lay on top of the existing floor, losing about 25mm (1") off my room height. Some of my floors are solid concrete and some suspended on timber rafters. Pre-slotted fibre cement tiles, that provide the ground insulation, are laid dry onto the floor and glued together. Moulded plastic sections are added at the ends where the pipe loops round into the next slot. The pipe is pushed into the slots to give a flush surface. It is split into several zones, each with a servo valve and room/zone wall mounted adjustable thermostat. I laid a 6mm laminated wood floor finish on top. In some places the laminate is left bear and in others a carpet is overlaid. It took me about 2 weeks to do a whole house (about 1000m²) but I did redecorate throughout while I had clear rooms to work with. A lot of the time was spent clearing rooms of furniture and reinstating afterwards. I brought in a contractor to connect gas to the new boiler (a legal requirement in UK), but otherwise I did all the work myself. Cost including new gas pipe, boiler, flue, slotted insulating tiles, pipework, servo valves, thermostats and gas contractor, and new laminate flooring approx £4050. (And my wife spent about the same again for decorating materials, new lighting, curtains, carpets, and furniture. Those hidden extra costs can mount up alarmingly.)

Energy prices in the UK have hiked about 25% in the last two years so a straight cost comparison with a conventional radiator systems is difficult. A sensible estimate would be that I have saved 30% on my space/water heating bills.

See www.polyplumb.co.uk.

Hello in your description I miss two important things: 1) over your subfloor a thin but closes polyethyleen foil needs to be placed that under no circumstances the concrete milk runs some where and changes the consitency of the LWC - can create cracking of the LWC which is no good. 2)Insulation below the piping - in my house this is a 30mm styrofoam plate as you do not want to heat the floor or the basement.

3) you need to discuss also what kind of LWC is used there are different types cement based and so called anhydrid LWC. Zement based can only span ~20 feet then you need a tension reducer gap or you get cracks - which is not good especially with a wooden substructure as this can move and then the tubing is stressed in these places- anhydrid LWC is not limited in the span width.

Consider also that LWC needs curing - for some time zement based is slower.

Crew or non crew - get it real flat and 100% - needs a crew of experienced man - considere setting of the material

Another option to wet LWC - I do not know whether this is available in the US- is dry LWC. This material is lighter than the LWC. The piping has to be installed in a styrofoam "system plate" to have a flat surface. On to of this a grid from strong cardboard strips 1inch high is nstalled and the grid is then filled with "dry LWC" wich comes in 25kg sacks. Above this you install OSB as base for the flooring. Might be you look for such a DIY solution system in the market.

Sounds to be an expensive and messy process... I chose to apply the "KISS" method, and went with a self-built system using 3/4" pex between the joists, with reflective insulation stapled to the bottom of the joists...The entire system cost less than $2K, including an electric boiler and I am happy with the resulting comfort... My floor is a 3/4" wooden sub-floor overlaid with 3/4" T&G hardwood.. The joists are 24" apart and each joist cavity has two runs of pex... I used no fancy "heat transfer plates... I live in Canada, so the system has to "work" or we freeze :-)

Check http://www.radiantdesigninstitute.com/ before you commit to your estimate...

I like your idea, what is the temperature of the water going through the tubes?

120 degrees and from my reading, it seems one can use even lower temps...

Such low temperatures are ideal for ground source heatpumps and great savings on heating bills

also check www.radiantmadesimple.com

First of all: get at least two more estimates, preferably using different methods of installation. Secondly I would not use sand. One of my frinds parents used sand for sound insulation in a new house many years ago, and in spite of a lot of precautions taken to prevent the sand from moving, it started leaking into the home after some several years and has been ever since. Needless to say it will be very expensive to remove it all.

Good luck, F

one interesting method of sealing the sub-floor from sand moving downward, is to use tin foil in between the sleepers. This also reflects heat upward. Rigid insulation is used also under the sub-floor.

what arte you going to put on top of the floor would be my question. Sand would also make great bedding for bugs that might get into the home

After the sleepers are installed, everything is sealed, before gyp or sand or concrete is installed.

sealed ? we both know that time and pressure will produce cracks in that seal