View Full Version : Radiant floor heat pex questions

11-26-2006, 12:01 AM
I'm building a house (all metal) with a concrete slab floor and will be using radiant floor heat. I plan on using pex tubing for the floor heating system. There are a few diffent types and few different types of fittings available. With virtually ZERO experience with pex I'm rather confused about what to buy. I've looked at products at Lowe's and Home Depot. Of course, the reason for buying off of the internet auction is the price.

One type of tubing that is totally new to me is Pex-Al-Pex or Flex-Al-Pex which are virtually the same thing. (a layer of aluminum tubing sandwiched between two layers of pex tubing). There's also Pex A and Pex B. Anyone with knowledge/experience of these products please give me some pointers. I'm not looking for the most expensive thing I can throw my money at. I'm looking for the best I can get at the best price.

The footprint of the house will be 2816 sq. ft. I need a very rough estimate of how many feet of 1/2" tubing I will need to put in the concrete using normal 1' spacing and doubling around the walls. If I have a couple of hundred feet too much that is no problem as I can use it later when I start on the upstairs sleeping lofts. ANY suggestions or advice will be appreciated.

I'll worry about the mixing valves, manifolds, circulating pumps, etc once I get the project above ground. For now I'm just planning zones and bringing the tubing up in a central location.

ALSO... I'm seriously considering an instantaneous propane water heater rather than a water heater set up for a heat source... pros & cons? (sounds stupid to some but it is being recommended by the manufacturer of the heater). This is in Alabama where radiant floor heat is extremely rare and most plumbing and HVAC companies don't know what the heck I'm talking about.

11-26-2006, 05:54 AM
The first thing you have to understand is that for heating purposes you either neither PEX with an oxygen barrier, or the aluminum inserted PEX which does the same thing. An additional benefit is that it will maintain whatever form you bend it in, without numerous clips to keep it where you put it.

11-26-2006, 06:04 AM
I just finished putting in a room of PEX which I got from Radiantec on the internet. They weren't the cheapest source, but they will give you massive support, and in being new to this thing too, I decided I needed it. They did everything from figuring the number of feet needed to diagramming the entire system. They don't make the PEX themslves and carry different types. I am planning to have a plumber come in to attach the system to my existing oil burner. Now this is where the expense is! I got two quotes from different plumbers and the quote was the exact same very high amount. Isn't America great? You can call two different workmen in and they have the freedom to give you the exact same price? What goes around comes around. Anyway, enough of my plumber rant. I suggest that you contact Radiantec, which you can find via google.

master plumber mark
11-26-2006, 06:20 AM
look around some more.....

I dont care for that Kitech type of Pex with the

Alluminum core....because once its in the concrete

its there forever....

Look into the Wirsbo type pex made for radiant heating....

its much more reliable and you dont get into troubles with

fittings later on down the road....

the expansion type witht he palstic rings are the best path...

its only a matter of not being
afraid of the expansion type rings and the
wirsbo tool you need to get....

as far as the KITECH here is a link to some disasters


their is some information about some condos in Oregon that made the
news and the hydronic disasters involved but I cant find the info anymore....

11-26-2006, 08:51 AM
Thanks for the reply. The one house I've been in which has a super fancy geothermal radiant floor heat system used Wirsbo.
MARK... I clicked on the link and got a "page not found"...hmmmm

I'm familiar with the oxygen barrier concept. Supposedly one of the big selling points other than the aluminum retaining its shape is that it has a lower expansion coefficient which supposedly helps minimize cracking the concrete due to expansion. I forget the theory but was told that in my application a two pour slab is not needed but that the aluminum variety supposedly eliminates the two pour method (slab on top of slab). As for it being in the concrete and always will be there... hm..well, that's the idea! As for leaks. I would think that a good installation and pressure testing before pouring should eliminate that unless there's some jacka$$ who can't protect the tubing while making the pour. I plan to use plywood sheets for walkboards while pouring and leveling the concrete. This should give reasonable protection for the tubing. Advice and correction to my plan is more than welcome. The popular "warranty" given to concrete is that "it will get hard and crack"......

11-26-2006, 09:52 AM
I'm familiar with the oxygen barrier concept.
I don't understand the concept, why you would need an oxygen barrier for hydronic heating if you don't need it for normal hot water in the house use.

I would think that a good installation and pressure testing before pouring should eliminate that unless there's some jacka$$ who can't protect the tubing while making the pour. I plan to use plywood sheets for walkboards while pouring and leveling the concrete.
I did a hydronic heated floor 10 years ago with that good poly bute pipe, so far no leaks (but then no pressure either). The concrete guys work like they get paid by the job and not the hour, good luck moving the plywood, and they use hoes to move the concrete... I had my tubing pressurized so if they did cut it, I could box out that area for repair later. I layed out the piping on 1' centers tywraped to 6"x 6" remesh, area was determined by how long the piping was in the coil, in my case it was 500', I know you can get pex in a lot longer coils. Mine is solar heated.


11-26-2006, 12:43 PM
Rancher.. I would hope that people working concrete would use a bull float rather than a hoe to move the concrete when working with the radiant heat tubing. I'll be right in the middle of it all when my floor is poured and you bet I'll be ready to kick some butt if I see anyone doing anything that might damage the tubing...the REAL heart of the system.

As for an oxygen barrier... I clipped this info from a site I found doing a search. It should answer your question.

Oxygen Barrier vs. Non Barrier vs. PEX-AL-PEX

Non Barrier tubing (Wirsbo Aquapex, Zurn PEX) is mainly used for PEX plumbing applications or radiant heat systems that do not contain any ferrous components.

Oxygen Barrier tubing (ThermaPEX,Wirsbo HePEX) is the most common tubing for radiant heat applications. Oxygen barrier and PEX-AL-PEX tubing both contain the oxygen barrier necessary to prevent oxygen diffusion. Oxygen diffusion refers to the ability of oxygen to pass through certain materials such as PEX. The problem with oxygen diffusion is that it can cause corrosion of metal(iron, cast iron) components in a Radiant Heat or hydronic heating system.

Finally, PEX-AL-PEX Tubing (Mr. PEX-AL-PEX, Wirsbo Multicor) is most commonly used for outdoor applications such as snow melting or running a supply line from an outdoor furnace.

11-26-2006, 04:39 PM

Now it comes back to me, they were using the hoes to pull the 6 x 6 remesh up into the center of the 6" slab... I would have perfered in hind sight just to have left it where it was, it was an anchor for the pipe, not for reinforsement. Still not sure what is the real problem on the oxygen barrier, so if I use copper piping and bronze pumps and a PE tank with PEX, I wouldn't need the pex-al-pex?

Next thought, same thread... hydronic heating of the slab... has any one used styrofoam under the slab? My Concrete contractor was very hesitant to try that due to the drying of the slab. Thoughts?


11-26-2006, 05:20 PM
I'm not totally familiar with all types of pex but I do know that Pex-A and Pex-B have the oxygen barrier. These are also recommended for drinking water and heating.

As for your question about styrofoam... after my research I doubt I'd want a floor of my home without the insulation under the slab. It is HIGHLY recommended for energy efficiency. There is at least one company producing styrofoam forms for the footings and sheeting for under the slab. I have a very good source and was able to purchase 2" styrofoam in 4'x8' sheets for $12.08 each (wholesale distributor cost, factory direct)... I bought 104 of them. The price at the big home improvement stores was like $28 each... so it was a good deal.

I will be using 1/2" re-bar spaced 12" in a 4"-5" slab. I had some of the sheets of styrofoam ripped into widths to form the footings. This has been the most difficult part. I had to glue these together with liquid nails and have to have very close tolerance to have a good bed to place the styrofoam for the footings so it will stay in place while pouring the rest of the slab. I'm probably going to reinforce the styrofoam with 2x4's then fill in or pile dirt against it as needed to help hold in place while pouring the footings. The outside wall of the form is 4" higher than the inside wall to act as a grade guide as well as to do the insulation. I've got my plumbing in the ground and most of the work done ready to install the styrofoam. I'm holding up until I get a post hole auger to dig holes for piers where I filled in around part of the footing. Also, I still have not purchased the pex I'll be using. This will be my home and I'm building all by myself with very little help so I anticipate that it may take me 5 years... more or less building as the money comes in since it's really a project and I'm wanting to be free of the costs and pains of financing.

master plumber mark
11-27-2006, 04:49 AM
Here is a very informative site for you

about the wirsbo porduct, though I cant understand

why you would want to go through all this trouble in


but to each his own..

http://hydronicradiantheating.com/ (http://hydronicradiantheating.com/)

11-27-2006, 06:10 AM
Mark... you're right about your remark about Alabama. That's the general concensus. However, it is slowly cathcing on here. It is the most comfortable heat. To me, it only makes sense. I hate cold floors. I probably have missed the point but most info simply says that it's not economical in Alabama. I don't know that I understand why it would be economical elsewhere but not in Alabama. It might cost me $1000 more than a conventional system (material costs) which is cheap for a long term investment and hopefully it will add value and comfort to the house.

12-11-2006, 10:11 AM
I would like your opinion. I am going to install radiant heating in my master bedroom. It is located over the garage (non conditioned space) and I must apply the tubing and joist trak (metal) under the floor thru the joists ( I can not remove the subfloor because it is glued, therefor I have no choice).
I would like any suggestions as well if I should use Wirsbo or anothe companies tubing like Thermaflex, as well as some one elses trak, ie, RHT.
I awaite a response. Thanking you in advance. SALVATORE

12-11-2006, 10:31 AM
My research has shown the pex pipe attached to the joists or to the underside of the subfloor using clips much like conduit is attached to a wall or beam. Once everything is in place then insulation is placed to cover it. If you're only doing one room then you might consider using the electric underfloor methods. There's plenty of information on the internet about all kinds of radiant heat. I posted here to get it directly from people who have installed or used the various techniques/methods. I'm sure the products are good but everyone thinks they've got the biggest and best product. It's the users whose opinion I trust the most.

12-12-2006, 08:29 PM
Thank you Randtj

12-14-2006, 10:15 AM
Before you determine how much tubing to place in the floor you need to have the heat losses for the house calculated. Then you can determine how much tubing to lay. It is frequently spaced differently at outside walls/windows. I believe Slantfin and Wirsbo have free calculators.

Under the floor you should have sand/gravel, a vapor barrier, insulating foam sheet, tubing, steel, and concrete. Under slab drainige as needed. There are plastic staples that are easy to use to attach the tubing to the foam. Then you can put the steel over it rather than attach the tubing to it. It is faster and less work this way. And if you make relief or decorative cuts it keeps the tubing safer. Do have air pressure in the tubes when pouring.

You ought to insulate the footers. You can get higher strength foam board at a lumber yard (probably have to be ordered) to satisify engineering requirements under the footers.

The heat loss calcs will also let you determine the size of the heat source.

Keeping loop lengths similar helps when controlling the zones. The amount of heat necessary will be a factor in determining the tubing size (1/2" is common). There are limits to individual loop lengths. You will be circulating the heated water and that will mean water returning to the heat source will already be pretty hot. Many instant heaters can not deal with hot water input while maintaining the proper output temperature. A boiler would probably be a better alternative. You can use the boiler with an heavily insulated indirect DHW tank to supply DHW. Using gas you can get condensing boilers that can extract as much as 98% of the energy. Much more efficient than instant heaters. A boiler and indirect DHW can provide much more hot water than a hot water heater.

For efficiency you want to run the loop water at the lowest temperature that meets your heat loss calculations. This is handled in the desing process.

You may need manifolds scattered about the building that distribute water to the individual loops. These have the valves that turn an individual loop on and off and can have balancing adjustments. You will probably need at least one in the system. If they are distributed you obviously need to plan for them in the structure.

Control, particualrly if you use more than one zone, can get a bit complicated. You might want to have a radiant heat person do this.

With a condensing boiler you will need a drain for condensate. It should be run through some marble chips before putting in the sewer, but many people do not do this. You probably would not want to drain this into a septic system.

Be very sure you know where things will be after the cement is poured. You must know where the tubes are if you need to use nails or other fasteners in the floor. Take picture with some means to be accurate when looking at the pictures to see where tubing is placed. Examples of things that need holes are toilet bolts for Toto toilets, fasteners to attach wall plates, floor mount equipment.

Done properly this is not as simple as it may look.

NEVER build an "open loop" system. This is where the DHW and floor pex share the same water. The loop water can have stagnant areas and if you drink the water or shower from the loop water it can buld up dangereous bacteria (e.g., liegonairs).

12-14-2006, 11:11 AM
alternety... you are saying to pressurise with air while pouring... other info I have says to pressurise with water to keep the tubing from floating up before the concrete cures.

As for the open loop system... are you suggesting that you tee off the water supply to a water heater/boiler which the water is circulated thru? For some reason I was thinking that even when the heat is turned off that a properly designed system kept water circulating at all times so that it stayed fresh and was diverted either into the hotwater tank or hot water supply so as to avoid stagnation.... I need to look deeper into that. Thought the mixing valve took care of that.....

12-14-2006, 05:46 PM
While some systems advocate using the water heater as a source for radiant heating, I don't think it is a great idea. In the winter, you might have an extra 1000' of piping to move the water through - you are likely to have some places to stagnate some water. In the summer, you don't want that water hot, so then what. Use a heat exchanger so you have a closed system, and a boiler. Most wh aren't designed for the continuous use you might need in the winter, and if sized properly, you then might not get enough to take a nice shower, either.

I think you'd be better off with a boiler dedicated to the task that you can turn off in the winter.

12-15-2006, 09:48 PM
Air works fine. The pex should not be free floating and will not rise to the surface. It needs to be attached. A little air makes bubbles; water makes damper spots in wet concrete. Use high pressure (50psi or more based on tubing rating). Watch the guage during the pour. The way to spot damage is to see pressure drop. Air is nicely compressable. If the house will not be completed and heated before freezing temps you may make a very long skinny popsickle (that can be agressive to components).

Research it. Sharing potable and heating water is considered a bad idea except for some online stores that sell junk systems.

Mixing valves do something else entirely.

Water heaters have much less burner capacity to heat water than a boiler. You can get a wide range of boiler BTU capacities. Water heaters are much less efficient. DHW can be a major component of your fuel bill.

Nothing makes sense until you know what the heating load of your house will be. It is not completely clear in my mind what you are actually trying to do. Trying to use one water heater for DHW and heating will most likely cause bad results under most any heating loads.

I am not sure what your climate is like there. Keep in mind that radiant slabs are not particularly responsive. There is a great deal of thermal mass there. You will not be happy trying to trun it on because of a cold night and then stop in the morning.

From some of the things you have said I strongly advise a lot more research or getting a pro to help. You might be able to find a reputable radiant heating person who will agree to let you pay for just a design. This can be tricky also; there are lot of prople that do this for a living but still do not understand. DIY of heating systems can be dangerous and create a system that may under perform and it will be too late to design it correctly. It is (wait for it) cast in concrete.

12-16-2006, 05:19 PM
Hi everyone,
I would like to know who makes the best pex tubing for radiant floor heating.
What size is the best for joist applications. Where is the best place to buy pex? Thank you in advance.

12-16-2006, 05:57 PM
Salvatore. From all of my reading it's just not likely that you will beat Wirsbo and it appears to have been proven in all kinds of applications. There are others and a few variations. In certain parts of the country a two pour method is advised. Here in Alabama the weather and climate are so totally different that the whole concept is not very well developed for this area. The fact that the whole floor slab acts like a heat bank appeals to me as well as the physics of radiant heat. For what I've studied I should be able to circulate it in one water heater and use that in series for the hot water supply. I'm thinking that controllers will shut off hot water and allow cold or warm water to flow thru zones that are not being heated... the other option is a heat exchanger and boiler system. I'm still studying and still have not installed radiant floor heat before... but it is being done here and I'm anxious to learn all I can about it...and start installing for customers.

12-16-2006, 08:16 PM
The a,b,and c, after the word PEX is a reference to the X linking method used by the Mfg.

12-17-2006, 11:23 AM
I heard from several non professionals that Wirsbo is over priced, but good. Thermapex seems comparable but perhaps twenty percent less.
Randyj, thank you for your comments.