# Hydronic Heating - pex location



## doc- (Jun 26, 2015)

Waiting on final blueprints before we break ground to build an earth-berm house. Planning on wood-fired boiler system to provide heat, the question is where to locate the distributing pex tubing: in concrete under floor or above concrete, between the concrete and the floor boards? (actually, above concrete, between sub-floor and floor)

I'm thinking the latter: placing the pipes in the concrete as we pour is a real PITA and makes later repairs and adjustments a real problem. With pipes just under the floor, the concrete then serves to insulate from heat loss into the soil instead of acting as a direct source of heat loss.

Any thoughts? Any experiences?


----------



## painterswife (Jun 7, 2004)

I have mine in the concrete. I would only go that way personally. We did it all ourselves and it was quite easy and we have not had one problem in over 15 years.

I would have the manifolds above the floor because it makes it much easier to bleed air out of the system.


----------



## jwal10 (Jun 5, 2010)

IF above, the heat is not in the concrete keeping it warm and dry. IF above I would want something to insulate and direct heat up (foil insulation) like is used in electrical floor heat. I like the idea of sleepers, subfloor and floor but is a lot more expense and the possibility of hitting the piping with a nail....James


----------



## melli (May 7, 2016)

doc- said:


> Waiting on final blueprints before we break ground to build an earth-berm house. Planning on wood-fired boiler system to provide heat, the question is where to locate the distributing pex tubing: in concrete under floor or above concrete, between the concrete and the floor boards? (actually, above concrete, between sub-floor and floor)
> 
> I'm thinking the latter: placing the pipes in the concrete as we pour is a real PITA and makes later repairs and adjustments a real problem. With pipes just under the floor, the concrete then serves to insulate from heat loss into the soil instead of acting as a direct source of heat loss.
> 
> Any thoughts? Any experiences?


Yeah, just came across a new in floor system that holds pex in a preformed mold....you put it above concrete, it is the sublfoor, I think....
It isn't Amvic, or this one...http://www.comftemp.com/thermalboards.html
I think it is this one:
http://www.warmboard.com/
At any rate, some research is in order, but I'd get the one with the best thermal conductivity upwards...warming up a concrete slab is a waste of money, and it takes a long time to change temps. 
I'd want one that is responsive to thermostat changes, which usually means the heat is radiating upwards.

Yeah, Warmboard is the best I've seen....just had a look at their site. I like it for so many reasons, ease of install, ability to repair, and lower temps required to operate. Have no idea as to cost...your just paying for the sheets of preformed pex-ply. 
I am seriously going to consider it for my shack...


----------



## Steve_S (Feb 25, 2015)

I put my 7/8 Pex into my Frost Protected Concrete Slab. Was easy enough by zip tying it to the reinforcement mesh and having the head unit (manifold) in place before the pour...

The advantage is the radiant heats the thermal mass of the concrete which once at temp will stay there. KEY is to make sure the thermostat sensor is centre to the floor inside the mass and linked to the air.... This solves problems if you have other heat sources that heat the air which can shut off the thermostat, stopping the radiant heat.

The concrete Slab is a Large Radiator and if properly built & insulated is a wonder retainer and slow release. NOTE that I used a FPSF SLAB. That has 4" XPS under it and extending 2' past the foundation & 2" XPS on the sides with 24". Code in my area (Zone 4, Ontario Canada) requires only 2" of XPS (R-10).

Putting it on top of concrete is NOT a good idea... You are then not only heating up, but down as well and it will always remain cooler, driving the heater more, shortening lifespan.... It also negates being to properly use the in-floor sensor so you will get random heating cycles.

I got my entire setup, parts & Takagi Heater (cheaper than anywhere else BTW) from http://www.radiantcompany.com/

Check out their documents, videos (they are excellent) and feel free to call them, they are very helpful & knowledgeable and will help you design the best system to match your build.

Also consider your Hot Water ! The radiant system can ALSO provide you with hot water using a bypass system OR an exchanger system... There are a few possible configurations depending on your use & needs. Myself my heat is using anti-freeze (Propylene Glycol) so it is a closed system, my hot water runs from a separate On-Demand unit.


----------



## Fishindude (May 19, 2015)

the normal deal is to level out and properly compact the sub base, lay down vapor barrier and a layer of rigid foam insulation, place welded wire mesh atop the insulation, then zip tie the pex tubing to the wire mesh to hold it in position when pouring the concrete.

Get a professional involved and pressure test those lines prior to pouring concrete. Also, break the pex up into multiple zones, so if a line ever happens to go bad, you don't have to shut down the whole house. You need to have a well compacted base, because if the concrete cracks and shifts down the road it could break a line and cause a leak. Also want to use care while pouring the concrete, so nobody damages a pex line.

It's a heck of a good system, done properly.


----------



## Darren (May 10, 2002)

I'd add that contractors may not know what well compacted means. It's something a contractor will short change, unknowingly, that may not show up as an issue for years. I've seen concrete crack in as little as a few weeks even when allowances were made for deliberate cracking for expansion or much longer dues to expansion issues.


----------



## wy_white_wolf (Oct 14, 2004)

Also have the pex pressurized while pouring the concrete. That way you'll see the bubbles if anyone damages it and can fix it before the concrete sets.

WWW


----------



## jwal10 (Jun 5, 2010)

They put PEX pipe under wood floors over a crawl space using metal deflectors to make the heat rise....James

http://www.houseneeds.com/learning-...ing-under-floor-radiant-heating-install-diary


Installing Radiant Heating Systems
There are several ways to install in-floor radiant heating systems.
&#8226; For installations involving a home renovation, it&#8217;s common to install the radiant heat tubing directly under a
wood subfloor from below. In this case, traditional fiberglass or a bubble/foil product is often used for added
insulation.
&#8226; Radiant heat tubing can also be installed within a plywood underlayment system &#8211; either directly over an existing
wood subfloor or over an existing concrete slab. For installations over concrete slabs, it&#8217;s recommended to
include traditional closed-cell foam insulation manufactured for use in damp locations.
&#8226; For new construction, radiant heat tubing can also be embedded within the concrete slab itself during the
pouring of the concrete.


----------



## doc- (Jun 26, 2015)

Thanks for all the replies.

The last couple of posts illustrate my point about in-concrete placement being a PITA to do and worse to repair.

Concrete is an excellent insulator, ie--it doesn't pass heat on easily, so putting it above the concrete helps slow down its passage into the ground. While concrete is a good source of heat once up to temp, it takes longer to get there and longer to cool off once warm weather comes. (My source of fuel is free, so that small bit of efficiency from heat retention is not a big deal and the "heat momentum" is a drawback.)

The boiler is wood burning, so is essentially always "on." No wear & tear on the system. We could also argue that without the concrete acting as a radiator, the circulating pump will work longer. That means it's cycling less, prolonging, not shortening its life.

The subfloor also acts to insulate the heated pex tubing from the concrete/ground, particularly if a reflective barrier is used. Sum total: less heat being wasted into ground.

I just don't see any important disadvantage to staying out of the concrete and many advantages.

Keep trying to change my mind, tho. I'm a good listener.

PS/ I just realized that maybe I should explain: the subfloor/flooring will sit on 6" joists above the concrete. Plumbing will run in that space, not buried in concrete. So pex in concrete would require first heating the concrete, then the air under the floor, then the flooring, then the air in the living space. Pretty inefficient.


----------



## jwal10 (Jun 5, 2010)

Page 11....James

http://www.warmboard.com/sites/default/files/downloads/Warmboard-R_InstallManual.pdf


----------



## Steve_S (Feb 25, 2015)

@Doc

Take all advice & suggestions with a grain or two of salt and check the FACTS out for yourself. That includes my own comments from my own Real World Experiences. Understanding thermal bridging and using high density mass for heating & cooling is not simple and not expected from the average people.

do check the links provided and learn as much as you can.... The radiant floor co has good, tangible, credible info & *many years of experience*. In fact many comments here echo some of that exp. they will even design zones & runs for optimal results to your particular region & build method.... it's no charge either !


----------



## melli (May 7, 2016)

doc- said:


> Thanks for all the replies.
> 
> The last couple of posts illustrate my point about in-concrete placement being a PITA to do and worse to repair.
> 
> ...


Yep, I agree, staying out of concrete is the only way to go...imho
Concrete has good thermal mass, but if your heating the subsoil, that is a waste. 
With only 6" space (assume joists are sitting on concrete or 6" above concrete?), you'd be hard pressed to crawl underneath and staple pex to underside of subfloor. I like the warmboard idea by far....it has built in reflectors. Repairing is possible...pressurize line once laid, so when you install wood flooring etc., you'll know immediately if you punctured line.


----------



## wy_white_wolf (Oct 14, 2004)

doc- said:


> ...PS/ I just realized that maybe I should explain: the subfloor/flooring will sit on 6" joists above the concrete. Plumbing will run in that space, not buried in concrete. So pex in concrete would require first heating the concrete, then the air under the floor, then the flooring, then the air in the living space. Pretty inefficient.


I'm wondering how you're planning on ventilating that space so you don't end up with moisture building up and rotting the joists away?

WWW


----------



## haypoint (Oct 4, 2006)

Those pre-cut flooring with spaces for PEX is awful costly. Plus you are destroying the benefit of radiant heat, thermal mass.

The drawback for wood heat is the temperature variations. With the slab as your thermal mass, it evens it out a great deal. 

Sure it is a PITA to run the PEX in the forms, but running re-bar and keeping it centered in the slab is troublesome, too. PEX is designed for in concrete construction.

Earth bermed homes have special concerns and need expertise to avoid problems. If running pex is too much for you, I hope you have a General Contractor with bermed experience.

Heat always rises, you are not heating the subsoil.


----------



## melli (May 7, 2016)

haypoint said:


> Those pre-cut flooring with spaces for PEX is awful costly. Plus you are destroying the benefit of radiant heat, thermal mass.
> 
> The drawback for wood heat is the temperature variations. With the slab as your thermal mass, it evens it out a great deal.
> 
> ...


Sorry, I have to disagree about not heating subsoil, and thermal mass being a positive. 
When you heat a concrete slab, energy is wasted, especially if one doesn't put loads of foam underneath...even then, your losing energy. I get the slab becomes one big hot plate, with more even heat radiation, but as far as 'true energy expenditures' goes, the less thermal 'bridging' the heated pex has to travel, the better. Hence, having it in sublfoor is about as good as one can get. Having pex exposed would be the best, but most folks don't like the idea of stepping over pex lines on the floor. 

Some homes probably still have those big cast iron radiators, that are heated by water...the reason they were used, is to minimize water cycling and to withstand the high temperature water being cycled. Over time, they went with rads that had copper piping, with aluminum fins. Better efficiency and boiler controls. This is the same deal with having pex in these specially designed subfloors. 

One can also get quicker temperature response...

Lastly, lower temps are required, which means it is easier to incorporate solar water heating systems. 

As for cost (warmboard system), what are they? I have no idea...

At the end of the day, one is looking to heat the air in the home as efficiently as possible. If your heating dirt, concrete, wood etc., on the way to heating air in home, your energy efficiency suffers.


----------



## haypoint (Oct 4, 2006)

melli said:


> Sorry, I have to disagree about not heating subsoil, and thermal mass being a positive.
> When you heat a concrete slab, energy is wasted, especially if one doesn't put loads of foam underneath...even then, your losing energy. I get the slab becomes one big hot plate, with more even heat radiation, but as far as 'true energy expenditures' goes, the less thermal 'bridging' the heated pex has to travel, the better. Hence, having it in sublfoor is about as good as one can get. Having pex exposed would be the best, but most folks don't like the idea of stepping over pex lines on the floor.
> 
> Some homes probably still have those big cast iron radiators, that are heated by water...the reason they were used, is to minimize water cycling and to withstand the high temperature water being cycled. Over time, they went with rads that had copper piping, with aluminum fins. Better efficiency and boiler controls. This is the same deal with having pex in these specially designed subfloors.
> ...



We have different opinions.
The subsoil is far warmer than the surface, in the winter. Often 50 or 60 degrees warmer. While foam insulation is recommended under a slab, nothing close to wall or ceiling insulation is recommended, for the reason I just noted.
Not a hot plate, a heat sink. As the PEX heats it up, concrete holds heat, as the wood fire dies out, it stays warm and continues to radiate heat. The greater thermal bridging, the slower the temperature peaks and valleys. Wooden subfloor is an insulation. The narrow strips of PEX will have to operate at a far higher temperature with so small a surface area, to heat the air. Your floor will be tepid in one area and scalding hot in another. A warm, evenly heated floor is a great comfort.

Those big heavy cast iron radiators filled with many gallons of hot water served as heat sinks. It takes longer to warm them, but once comfortable heat is obtained, it stays at a far more constant temperature over a longer period, leveling out the ups and downs of a wood fire. Water cycling wasn&#8217;t an issue as many systems did not require a circulating pump to move the water. Remember hot water rises? In those systems, the warmest water was found in the second floor radiators and the coolest water was the 2 inch furnace intake pipe, at the base of the boiler.
Installing a circulating pump and operating several zones, cheaper to build and install is the copper and aluminum baseboard heating units. They work fine with oil fired or propane boilers.
You get faster temperature rise, with the downside of an hourly cycle of ups and down temperatures. 
With tiny areas of radiation, expected to heat the entire home requires higher operating temperatures.
I operated one of those old wood fired cast iron systems in a 5 bedroom home in one of the coldest areas of the US. The water temperature at the furnace never got above 110 degrees F. I have seen many of the aluminum and copper baseboard systems that operate from 180 near the boiling point.
Less fuel is required when you can maintain a home at a more constant temperature. Thermal mass provides that stable temperature. Any loss of heat energy into the earth below your foundation isn&#8217;t escaping. If anything, it&#8217;ll rise and add to the heat energy of your home.

My neighbor operates a boiler system and the solar water panels add hot water to his 30,000 gallon heat sink, to assist his wood fired boiler.


----------



## Fishindude (May 19, 2015)

Putting sub-framing and a sub-floor over top of the slab just adds a bunch more unnecessary expense. Do a good finish on the concrete and you can lay tile, carpet or laminate right on the concrete. You can also do a nice finish on concrete, stamp a pattern in it, or color stain it and just use it as the finished floor.


----------



## doc- (Jun 26, 2015)

haypoint said:


> . Heat always rises, you are not heating the subsoil.


Hot fluids rise. Heat photons radiate in all directions. With the cement in direct contact with the subsoil, which is always ~55*, it will lose heat to the soil faster than it will to air above it, a poor conductor.

I'm thinking we're arguing relatively small differences in efficiency-- not even much of a concern, given I have access to free fuel.

In regards using the cement as the floor: always 55* in warm months-- not beneficial to us ancient arthritics--and then plumbing would be embedded and repairs & improvements becoming a major project, all easily avoided by raising the floor.

The Warmboard costs appear to be ~$5-7/sq ft (!) I think I'm bright enough to run pex tubing without a pre-drilled groove to show me the path.


----------



## doc- (Jun 26, 2015)

wy_white_wolf said:


> I'm wondering how you're planning on ventilating that space so you don't end up with moisture building up and rotting the joists away?
> 
> WWW


Good point. Condensation is a major problem in any earthberm house. Insulation, venting and dehumidifiers need to be employed efficiently. Keeping the living area warm & dry enough in summer is a bigger problem than warming it up in winter.


----------



## painterswife (Jun 7, 2004)

Okay, there are some things being said here that are either not getting through to me or are wrong.

Concrete is not an excellent insulator. Are you pouring a slab and not insulating it from the ground?

If you are worrying about damaging pex in concrete then you are not planning and installing it correctly. Radiant in concrete is the best even heat in the long run. You can use any heating source from solar. wood, electric and gas to heat the water. The only drawback is quick response.

There also is always the option of pouring a slab insulating on top of that and then pouring a thin slab with the pex in that.

Radiant always works better when it warms a surface instead of the air between the insulation and the floor.


----------



## Fishindude (May 19, 2015)

*Hot fluids rise. Heat photons radiate in all directions. With the cement in direct contact with the subsoil, which is always ~55*, it will lose heat to the soil faster than it will to air above it, a poor conductor.*

You do not put the slab in direct contact with the subsoil, you put insulation under it so you are not heating the sub-soil. You warm up the mass of concrete slab.


*In regards using the cement as the floor: always 55* in warm months-- not beneficial to us ancient arthritics--and then plumbing would be embedded and repairs & improvements becoming a major project, all easily avoided by raising the floor.*

Untrue, in warm months your slab (installed over insulation) will be pretty close to same temp as the rest of the room. The Pex pipe is one piece continuous plastic tubing, and done properly all fittings are outside of the slab in an accessible location in the event they would ever leak. The only way you would have a failure is it you poked a hole in it while pouring the slab, or drilled a hole later in slab and penetrated it.


*The Warmboard costs appear to be ~$5-7/sq ft (!) I think I'm bright enough to run pex tubing without a pre-drilled groove to show me the path.*

You don't need this stuff. Lay down 2" blue board foam $0.50 /SF, then place 6"x6" 10ga wire mesh $0.15 / SF over that, and hold Pex tubing in position by plastic zip ties to the wire mesh.


If you build a sub floor on top of slab you will need treated 2x4 sub framing, Tapcon anchors, 3/4" OSB or plywood, then may need another layer of 1/4" Luan sub floor to accommodate some finish flooring types. All of this stuff is going to add up to about $1.40 / SF. I would also be concerned with condensation and mold in the cavity created between slab and underside of plywood.


----------



## melli (May 7, 2016)

Warmboard does seem expensive...albeit, you are getting the subfloor in the deal, and aluminum reflectors. 
Hopefully, the price will come down.

If I may clarify what happens for in floor radiate heating. Thermal convection and radiation (in infrared wavelengths) happens at the floor surface, as the floor is warmer than the air (when one has hot water flowing in pex pipe). 
Below that, from floor to pex pipe, it is thermal conduction (In solids, conduction is mediated by the combination of vibrations and collisions of molecules - wiki), where atoms and molecules, heated by pex pipe radiate outward until equilibrium is achieved. This is the area where we have several boundary layers...water in pex pipe, pex plastic, concrete (if used), wire or rebar, subfloor, and then wood floors, carpet, tile etc. Each of the above items have a different thermal conductivity. They also will conduct in all directions (in most cases). This is unlike thermal convection, where warm air rises because microscopically, the Brownian motion in hotter air creates a larger space between atoms, and consequently will be lighter than the surrounding air (will rise). 

My issue is all those boundary layers and materials...heat is lost traversing though all those materials, and jumping through different boundary layers. One could say, well, all that heat energy is preserved in floor. Well, I agree to a point. The materials through which the heat energy has to travel will go in all directions. Some will go down into subsoil (if no insulation under slab), and to a much lesser extent even foam insulation (it is not a perfect insulator). Some energy will escape out the sides of concrete, heating up footings, walls etc. That energy loss, relative to total energy input contributes to total efficiency of a system. 

When talking about radiant heating in floors, it isn't a closed system. Heat gets wasted (heats ground or outside air). 

This is why I feel warm board or equivalent is the best of the lot. It put the heat energy as close to the floor as one can reasonably get. Thermal conduction is limited to whatever one puts on top of warmboard. You get the best efficiency (period). 

As for comfort and hot spots, that is debatable. In warmboard, they have a sheet of aluminum to disperse (thermally conduct) energy over an area.


----------



## painterswife (Jun 7, 2004)

melli said:


> Warmboard does seem expensive...albeit, you are getting the subfloor in the deal, and aluminum reflectors.
> Hopefully, the price will come down.
> 
> If I may clarify what happens for in floor radiate heating. Thermal convection and radiation (in infrared wavelengths) happens at the floor surface, as the floor is warmer than the air (when one has hot water flowing in pex pipe).
> ...


I installed my radiant floor 15 years ago ( concrete on a wood subfloor). Warmboard was around then. The cost is not going down. Thermal conduction is not limited to the top. .It is not the best efficiency. It heats in lines and does not spread the heat out as well as concrete does. It also leaves your pex vulnerable to nails from above. It is much cheaper to just put down blue board and sleepers then to buy warmboard.

I work for a housing contractor. We have never had to go back to for repairs for pex in a concrete floor. We do have to go back all the time when pex under or over the floor gets punctured by a floor installer or home owner. You have to cut out a section of the pex and the add new with two connectors that can fail in the future.


----------



## doc- (Jun 26, 2015)

Whether or not a given material is called an insulator or a conductor is relative. What counts is the material's "thermal conductivity." Materials that take up heat slowly also give it off slowly and are called insulators; those that take it up quickly also give it off quickly. How quickly a material changes temperature depends on its thermal conductivity and its total mass. 

Heat energy flows in all directions. It flows via direct radiance (IR waves), via conduction (colliding molecules) and via convection (hot fluids rising). 

In conduction, the heat flows between two objects and the rate at which it flows depends on the temp difference as well as the thermal conductivity property of the two materials.

As Melli notes above, putting the pex tubing as close to the floor as possible would be most efficient. If the tubing is embedded in the concrete in this application, it will have to first transfer the heat to the concrete, then the stagnant, 6 in. layer of air (a good insulator,-- ie transfers heat poorly) then heat the flooring before finally heating the air in the living area.

With tubing in floor, besides the Al reflective sheeting insulating the bottom side of tube, the wood subfloor and that stagnant layer of air also serves to insulate heat loss to the concrete.

While the need to repair an embedded pipe may be rare, the cost will be huge.

Look at it this way: in a conventional house with a basement, do you put the pipes in the cement floor of the basement, or in the floor of the living area?


----------



## NorthwoodsMike (Jun 10, 2013)

I really think that you are making a mistake with the suspended floor over concrete. A thick plastic vapor barrier, and treated floor joists tied to a perimeter footing, forming a crawl space would be better. Pex could be attached to the subfloor using heat transfer plates, with insulation under that. This design allows for changes in the future.

For what it's worth, if you aren't going to be adjusting plumbing on a regular basis, you really wouldn't regret scrapping the floor joists and pouring the pex into concrete. The slab needs a vapor barrier and 2" insulation under it, but leaks don't form later, as it's fully encased in concrete. Pressure testing is a piece of cake, as is pressurizing during the pour. 

I have personally used both methods on our current home, and concrete only again at our former cottage. I designed both systems, and they work quite well. You can see pictures of my current home here if you search for "Our Northwoods Homestead." It shows the heat system install. Don't be afraid to ask me questions either. I did a ton of research on my system, and I'm happy to share what I learned.


----------



## haypoint (Oct 4, 2006)

doc- said:


> Hot fluids rise. Heat photons radiate in all directions. With the cement in direct contact with the subsoil, which is always ~55*, it will lose heat to the soil faster than it will to air above it, a poor conductor.
> 
> I'm thinking we're arguing relatively small differences in efficiency-- not even much of a concern, given I have access to free fuel.
> 
> ...


 Yup, hot fluids rise. But so does warm air. Otherwise the billion dollar ceiling fan industry would be out of business. Donât take my word for it. Check the air temperature in a room, measuring at the floor, 4 feet up and at the ceiling. Hot air rises.
Insulating under the slab will help, but not that much heat gets into the 55 degree subsoil, since heat rises. Energy efficient homes have far greater insulation in the ceilings because there is more heat loss through the ceiling than the walls or slab, because heat rises.
While a vacuum is a poor conductor of heat, heat rises/circulates through air with ease.
In the summer months, how warm do you think the wooden floor will be? When the heater is not circulating heated water through your PEX, the wooden floor will be close to 55 degrees. Cold concrete feels colder than wood, because wood is a better insulator. A ceramic tile floor is just as cold. Since even wood floors feel cold, most folks wear slippers or put throw rugs all over the place.
Since you are bright enough to run PEX tubing without a pre-drilled groove to show you a path, just how are you stabilizing the PEX? Under the subfloor?
In the warmer climates, many homes are built on a concrete slab. Water lines, sewer and even some electrical are encased in concrete. Iâve never heard of a major problem with water lines in concrete. Know anyone that lives in the South? Ask them if plumbing in concrete is a PITA.


----------



## Steve_S (Feb 25, 2015)

Sorry I have to say this....

Doc- WHAT do you really want from us ?
1) Hydronic Heating is used for "Radiator Heating System" not Radiant Heat - TWO separate systems and terms are NOT interchangeable.

2) Thermal MASS is concerned with heating up a MASS (the slab) and having it act as a long term heat radiator. This has been explained in a few different ways.

3) Many links with Credible, Valuable and CORRECT information have been provided for you to review and to help you understand the entire process... Yet you hold onto Wives Tales and issues from long ago that are no longer issues. PEX is the evolution of various materials that DID fail in the past... For example when Copper, Iron or PVC were used for Radiant systems.

4) You are fixated on inefficient design ideas (floating floors with air spaces) - Maybe this is the result of a lot of mis-information or misunderstanding.

Those of us who have used & are using Radiant Heat have shared our experiences and knowledge (1st hand info) and even with that I stated that you should verify everything for yourself with credible info.

Maybe you are not aware but even the Romans used Radiant Heating that provided warm air & hot water for the baths simultaneously... Other ancient peoples had similar ideas, including passive Air Conditioning... The concepts are NOT new obviously, yet have evolved and been refined and we have the knowledge & modern materials & science to our advantage.

Thermal Dynamics & Physics are not material to be taught in a forum such as this but the essential basics should have been covered within the standard K-12 education system, unless it really has failed as is becoming all too apparent.

I do NOT intend to be terse nor upsetting, so it is your choice to react negatively if you / anyone chooses to... My point stands, why are you asking and what do you want ?


----------



## painterswife (Jun 7, 2004)

I agree with Steve. I don't get what you are trying to accomplish. You are building a bermed house. You are already working the mass system. Mass and radiant heating justs work so well together. Why go with an inferior system?


----------



## doc- (Jun 26, 2015)

I asked the question to see if anyone comes up with some paradigm changing point that I haven't thought of. So far, no go. The main advantage of embedding seems to be limited to the thermal inertia of heating up the cement first. That's a disadvantage at the beginning and the end of the heating season. The thermal momentum of cement only leads to somewhat lower fuel usage, but at zero cost for fuel, that is not a factor.

Thanks for the input.


----------



## Steve_S (Feb 25, 2015)

Well there it is... Good Luck with your build and I hope it works out for you. 

Have a Terrific Day


----------



## painterswife (Jun 7, 2004)

doc- said:


> I asked the question to see if anyone comes up with some paradigm changing point that I haven't thought of. So far, no go. The main advantage of embedding seems to be limited to the thermal inertia of heating up the cement first. That's a disadvantage at the beginning and the end of the heating season. The thermal momentum of cement only leads to somewhat lower fuel usage, but at zero cost for fuel, that is not a factor.
> 
> Thanks for the input.


So you are going to go for an inefficient system because of a slight disadvantage at the beginning and end of the heating season. All I have to do is bake some cookies and I solve that problem because the mass of my radiant system already tempers the swings in temperature. I bet lighting a candle or two could do that in a properly built earth bermed home. How is that for some info you might not have considered.

I am at 6500 feet and it is trying to snow every day already. My 2 inch concrete floor (on a subfloor over a crawl space) provides enough mass to allow me to use very little heat, if any. Yesterday my husband did bake cookies and that meant we needed no extra heat even though it hit 34 outside.


----------



## melli (May 7, 2016)

I think Doc is just looking for opinions and ideas...
We all gave some compelling arguments, some of us at odds with each other. eep:

This thread reminds me of the metal roofing vs shingles debate...strong feelings emerged about that topic. :hobbyhors

At the end of the day, only Doc has to live in his home. 

BTW - I do get that pex in concrete has proven itself, provided one has sufficient insulation under slab, especially in a cold zone. 
I know of a neighbor who failed to put insulation under their slab and in winter that slab has become a heat sink...that is, their home heating bills have shot through the roof because they are heating the ground because of that slab in the basement. They were kind enough to admit their mistake. 

Although, in summer, it would be a great place to sleep at night on hot summer nights. 

Painterswife - I believe your system would be fairly efficient, since the slab is suspended and the slab is isolated from ground by a crawl space (air space). 

I do like to look at thing from a physics point of view, as that is what I did, and try to still do...and the objective, in my opinion, is to transfer boiler heat to the house air as efficiently as possible. Whether it is through radiators, hydronic heating or radiant flooring, is immaterial. Eventually, one has to consider costs...and what they can afford. 

The one sticking point for me, is the lower water temps required for warmboard. That really interests me, especially if one were to use solar heating. In my area, it is really catching on, given we are energy hogs in winter. 
I know Doc appears to have inexpensive energy at hand, so my suggestion may be a moot point.


----------



## painterswife (Jun 7, 2004)

My floor is insulated directly below the subfloor and around the edges of the slab. Otherwise I would be heating the crawlspace and that would just be stupid. All slabs with hydronics in them should be isolated and insulated from the ground or the stem walls. To not do that is just throwing money away.

Inexpensive heating sources do not negate the need for proper systems and insulation.

A slab is the cheapest solution in the long run. It transfers the heat efficiently. He is already doing a slab, he only needs to insulate it properly. He needs to do that anyways. Slabs temper the wild swings in temp and allow you to use lower water temps. ( Mine is set at 105). You can easily finish the slab and use it as a floor. We did that. 

I could go on with the benefits to cost and comfort but I don't think it will make a bit of difference.


----------



## Steve_S (Feb 25, 2015)

My last post to this thread.

Here is a Document that discusses the proper way to build an FPSF (Frost Protected Slab Foundation). NOTE: Never Ever use SAND under the pad, always use a hard compactable fie gravel like A-Grade. Sand will shift & wash out even, causing voids leading to slab cracking. These errors occurred in some areas and in some cases still using sand, most codes have revised accordingly but not all. There are numerous methods & means BUT look at the Alaska Spec's which are very similar to our Canadian ones... These are commonly used with great success.

http://publications.gc.ca/collections/collection_2011/schl-cmhc/NH15-457-1998-eng.pdf

http://www.ecohome.net/guide/slab-grade-technical-guide

https://buildingscience.com/documents/profiles/etw-minneapolis-profile

http://foundationhandbook.ornl.gov/handbook/section4-1.shtml

Above you have a variety of design methods relative to climate zones + Some are slightly dated but still accurate.


----------



## melli (May 7, 2016)

Steve_S said:


> My last post to this thread.
> 
> Here is a Document that discusses the proper way to build an FPSF (Frost Protected Slab Foundation). NOTE: Never Ever use SAND under the pad, always use a hard compactable fie gravel like A-Grade. Sand will shift & wash out even, causing voids leading to slab cracking. These errors occurred in some areas and in some cases still using sand, most codes have revised accordingly but not all. There are numerous methods & means BUT look at the Alaska Spec's which are very similar to our Canadian ones... These are commonly used with great success.
> 
> ...


Last post? 
Your second link doesn't work. 
Appreciate hand books, research reports, and the like... :thumb::thumb:


----------



## NorthwoodsMike (Jun 10, 2013)

doc- said:


> I asked the question to see if anyone comes up with some paradigm changing point that I haven't thought of. So far, no go. The main advantage of embedding seems to be limited to the thermal inertia of heating up the cement first. That's a disadvantage at the beginning and the end of the heating season. The thermal momentum of cement only leads to somewhat lower fuel usage, but at zero cost for fuel, that is not a factor.
> 
> Thanks for the input.


I don't think you can really go wrong, in a slab, under the subfloor, or on top of the sub floor, as long as you insulate. That is key. 

You mentioned earlier that conductors/insulators are relative, and you are correct to a certain extent, but the better the r-value of the insulator, the better the system will work. Don't rely on an air space to insulate. Use real insulation under your subfloor. Your fuel might be "free" -but the fuel, labor, and the time used to transform it to a usable form is not.

I'm still puzzled by your desire to pour a concrete base, then put joists on top of it. Why the extra expense when a perimeter foundation and vapor barrier would suffice?

Also-here is the link to my build. This page shows the heating system. I've made a few changes to the pump configuration, eliminating the mixing loop, but you get the idea.

http://www.homesteadingtoday.com/homestead-construction/487777-our-northwoods-homestead-2.html


----------



## haypoint (Oct 4, 2006)

Motorcycle engines have aluminum fins to increase the surface area so the heat will dissipate faster.
Aluminum fins on a baseboard radiator increase the surface area, so the heat from the pipe will dissipate faster.
Air conditioners have aluminum fins and copper tubes to increase the surface area so the heat can dissipate faster.
Automobile radiators have fins to increase the surface area so the heat will dissipate faster.

A red hot horseshoe will burn you. But drop it into a pail of water and the heat is transferred to the water making the water warm.

A one pound red hot horseshoe will not warm a cold room. But a one pound red hot sheet of thin metal will warm a room. Surface area is the key. 

A 400 degree wood stove in the corner of a room will not heat a room as well as ten 200 degree wood stoves placed around the room. 

100 feet of scalding hot PEX pipe laid across the floor in one room will not heat as well as 100 feet of warm PEX imbedded in concrete, due to the increase in surface area.

With unlimited surface area, you could heat a room with 78 degree water. 

After 30 years with a wood fired boiler and tons of cast iron and water, I can't stand homes with forced air heat that kicks on at 71 and off at 76 several times an hour.


----------



## Fishindude (May 19, 2015)

* I'm still puzzled by your desire to pour a concrete base, then put joists on top of it. Why the extra expense when a perimeter foundation and vapor barrier would suffice?*

Me too?
That's like putting a roof over your roof.


----------



## Nordic1 (Dec 27, 2016)

Sorry for the late response but just joined. I have done all three houses I've built using radiant flooring. All were WIRSBO PEX with Viessmann oil-fired boilers, Tecmar controls and Grundfos pumps. On the second floors, in the first two I used metal heat transfer plates between 3/4" sleepers over the #30 felt covered plywood sub-floors then applied t&g solid hardwood strip flooring. After a Mutt & Jeff sub shot 16d framing nails through my PEX and ruined the flooring and the ceiling below, I switched to using Grace Ice and Water dam on the floor before applying the finish flooring. As it creates a waterproof underlay, and self seals, I figure it could at least mitigate some potential damage.

On all lower floors, I used 4" of 5-sack concrete with control joints at 10' centers with 2" of DOW blueboard underneath. On any floor placed on ground a thermal barrier is required, at least here in Wash. I have had very good performance from the heat transfer plates and the concrete. Some people place gypcrete between the sleepers, but it's messy and a pain. It is important though, to understand that the response time for the concrete floor is much slower than that of plates, but once at temperature the heat is more even. Also take into consideration any additional floor coverings such as area carpets.

If I can give you any advice it is to scrupulously diagram the locations of your PEX tubing, provide a copy to any subs, and make sure they agree to responsibility for any damage that may occur. If you don't, later on you or any future owner will not know where to nail or screw and where not to. And, you'll likely avoid what happened to me ( I even marked the exact PEX locations on the floors with a marker which the moron sub interpreted as the locations they SHOULD nail! Well, live and learn.) 

Also, if you're doing concrete, make sure any wire-rebar ties are turned under before placing the PEX above the rebar, or do what I did and use zip ties for the rebar cross connections. And, make sure the concrete guys watch their step and do not use a concrete saw to cut control joints, but strike them in.

Lastly, make sure your contractor is certified for the PEX system you are using, and for the controls. If you want to save money, and are a technical type, do what I did, take the PEX cert and controls cert courses, and get a specialty contractor license. Then you can obtain the materials at contractor cost, design the system and its zones yourself, and install it. I probably saved *K on the most recent home I did.

Installation is really quite easy as long as you've done your design homework related to zones, temps and flows. The most difficult part is the zone manifold, pump and boiler controls, but if your technically inclined, it is really not difficult with cert training. If you're not that adventurous, make sure your contractor is certified on the PEX system, the controls system and the boiler system. Well, that's my two cents. Happy to answer any questions. Good luck Chris


----------

