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# Underfloor Heating With Wirsbo Joist Trak &amp; Wirsbo 1/2” hePEX

Member Posts: 29
I want to install supplemental heat under the tile floor in our master bath. The subfloor is 3/4” plywood and the tile with mortar base is 1-1/2” thick. I plan to use Wirsbo Joist Trak with Wirsbo 1/2” hePEX to deliver the heat to the underside of the master bath subfloor.

The joist bays have been reduced in width from the normal 14-1/2” width due to additional 2x12 joists that were added 16 years ago to cantilever out the back of the master bath. The widths of the joist bays I want to run two Joist Trak panels side by side in vary from 9-3/4” to 12”. I can maintain 8” center to center in the bays 11-1/2” and larger, but will only have 6-1/4” center to center in the 9-3/4” bay.

According to the Wirsbo data sheet the minimum bending radius for Wirsbo 1/2” hePEX is 6 times the tubing diameter. When determining the minimum bending radius for Wirsbo 1/2” hePEX do you multiply 0.5” or the actual OD of 0.6275” by 6?

6 x 0.5” = 3.00 radius and the Joist Trak can be located a minimum of 6” center to center. This limits the minimum joist bay to 6” + 3.5” = 9.5”.

6 x 0.6275 = a minimum 3.765 radius and the Joist Trak can be located a minimum of 7.53” center to center. This limits the minimum joist bay to 7.53” + 3.5” = 11.03”.

Below are pictures of the 9-3/4” and 11” joist bays with Joist Trak and 1/2” tubing installed. I am concerned the 9-3/4” joist bay is too narrow to run two Joist Trak plates in based on the appearance of the bend in the tubng.

<img src="http://www.fototime.com/5CFA71D474C5FD4/orig.jpg" alt="" />

<img src="http://www.fototime.com/0473A75B3AA1180/orig.jpg" alt="" />

Below is a drawing illustrating how I plan to install the Joist Trak plates. Comments and suggestions are appreciated.

Thanks.

<img src="http://www.fototime.com/F64DA8A01016D9F/orig.jpg" alt="" />

• Member Posts: 3,086
3/8"

I never run 1/2" in joist always use 3/8". Much easier to pull and this issue would go away. You do not get more btus from 1/2" just the ability to run longer loop lengths. I like to see mine no longer than 210-220 which fits in the 3/8" wheelhouse.
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
• Member Posts: 5,839
Bobby pins and Cancer ribbons...

Your bends don't HAVE to be perfectly round, semi circles.

In your case, you have enough room at the ends of the runs to allow you to either use a bobby pin head loop (wider radius), or you can do a cross over loop, like the cancer ribbons. The crossover ribbons are a little tougher to do, but with practice and suspension clamps can be made to work, and if need be, you can do tubing at 2" O.C.

The reason I prefer 1/2" over 3/8" is due to the inherently higher pressure drop of 3/4" tube and fittings. My gut tells me it allows more flow, which is a good thing...

ME
It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
• Member Posts: 29
edited June 2011
RE: 3/8"

Chris,

Thanks. I would consider your suggestion if I had not already purchased 300’ of 1/2” PEX plus the Joist Trak for 12” PEX. I expect it will be difficult to run the 1/2” PEX given the route I have to take. I plan on asking three friends for help pulling the PEX.

Howard
• Member Posts: 29
edited June 2011
Re: Bobby pins and Cancer ribbons...

Mark,

Thanks. I downloaded the Watts Radiant Installation Manual and it is much more informative then the installation manual from Uponor (Wirsbo). In the Watts manual they describe the bulb (your bobby pin) method. They also use the OD of the PEX to determine the minimum bending radius, but they use a multiplication factor of 8 where Wirsbo uses 6.

If I use 5/8” as the OD for the Wirsbo PEX and multiply by 6 that equals 3-3/4” radius so a 9-3/4” joist bay will be acceptable if a bulb shape is formed. To do this how far past the end of the plates should the tubing extend and how and where do you support the bulb shape head so it maintains its shape and does not unzip the tubing from the plates? Below is a picture of the 9-3/4” joist bay where I have extended the PEX tubing to let a bulb shape to start to form.

BTW, I have Wirsbo bend supports that allow for a very tight radius, but I believe these would interfere with the required freedom for tube expansion.

Howard
• Member Posts: 3,086
edited June 2011
Flow

Mark you know as well as I that flow required is based on the heat loss of the room. If the room required 2gpm @ 3ft of head which pump would you use? If the room required 2gpm @ 5ft of head which pump would you use? The point of making you get better flow with 1/2" over 3/8" is a matter of the proper sized circulator based on the head it must overcome. I've never done a radiant job where the head exceeded the curve of a 007, 15-58, or 00R type circulator in 3/8" so why would I use 1/2"? Do you feel this bathroom would?

To the poster, get rid of the bend supports. Not necessary, you can use a tube talon/snail clamp at the center of the bend if you desire to secure it.
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
• Member Posts: 5,839
Chris....

I haven't used either of the pumps you recommend since there were DCECM circulators on the market. I also haven't used a bang bang thermostat in about the last 10 years.

We design differently. My systems modulate in every way currently possible. I only want to use what I need to use to satisfy the load, and the less of any given Item (watts, BTU, GPM) I HAVE to use to deliver excellent comfort is beneficial to the end user. I design for customers who are extremely energy aware. EVERY watt counts. I design for long term energy efficiency.

You have to design for lowest first cost (to some degree)

You design for contractors who are mostly "first cost" aware in an effort to get work. They need to concentrate on selling the sizzle and quit concentrating on the steak. They will get a higher premium than their competitor.

You're right for the most part. 3/8" tube compared to 1/2" tube may not make that big of a difference in the cost of supporting casts (pumps), but that is not how I look at things. I look at things in the LONG term, and again, every watt counts. And if I can satisfy a given load with a higher flow rate using less wire to water energy, but a lower operating fluid temperature due to a given tighter differential, then that makes my system different (more efficient) than yours, and that is the way I prefer it.

To each, his own. They both work. But mine is more expensive than yours. Honestly, I can't remember the last time I was the low bidder....

Peace...

ME
It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
• Member Posts: 212
supplemental heat

Dont over-engineer this, its supplemental heat. As long as you have your primary source of heat in the bath, this is nothing more than floor warming. As long as you can get 2 pipes per bay, and are using a mixing valve to keep your water temp at about 140, you will be satisfied with the result.
• Member Posts: 5,977

you bought all the material.  For supplemental heat you were probably better off with a hydronic towel warmer
steve
• Member Posts: 29
RE: Flow

Thanks. I only showed the bend supports to show the tight radius that can be achieved with them. I had no intention of using them. Regarding your recommendation to clamp the center of the bend, it is my understanding you are not supposed to clamp there due to tube expansion.
• Member Posts: 29
RE: supplemental heat

Thanks. Plumbing with PEX and hydronic heating is completely new to me so I have lots of questions.
• Member Posts: 29
RE: It's too bad

Unfortunately a hydronic towel warmer will not warm your feet on cold tile.
• Member Posts: 29
More Questions

I have been delayed with health issues and I am going to try and move forward today. I am still working out the logistics of running the PEX tubing through the bays.

My best estimation is I will run 200 feet of 1/2” PEX tubing. At least 40’ of the run (20’ supply and 20’ return) will be located in the garage and above the dropped ceiling in the kitchen. Should this portion of the run be insulated and are there specific types of insulation I should use that will not react with the PEX pipe?

I plan to do the following.

– Separate the aluminum Joist Trak plates by 2”.

– Allow 18” space between the end of the Joist Trak and end of the joist bay where the PEX tubing crosses bay to bay. See drawing below.

– Allow 12” space between the end of the Joist Trak and any obstructions such as blocking or plumbing at the end where the PEX tubing is turned

I noticed one company recommends using 1/2” pipe insulators where the PEX tubing passes through a joist. These require a 1-3/8” hole be drilled in the joist and there is a snug fit between the insulator and PEX tubing. Are these a good idea or should I just drill 1-1/2 holes through the joists and allow the PEX tubing to move freely within? NOTE: If I drill 1-1/2” holes and use the insulators the PEX tubing can move freely.

In one joist bay a 7” vent pipe for the kitchen range hood resides and I was concerned about the PEX tubing contacting the metal vent pipe. Is there a good way to prevent the PEX tubing from contacting the 7” metal vent pipe at the end of the bay where the PEX tubing feeds through holes that must be 2” down from the subfloor? Is insulation sufficient? I don’t want this to be a source of noise or wear.

Thanks again for everyone’s input so far.
• Member Posts: 3,569

You may want to get your hands on a copy of the Uponor Joist Trak installation manual, which will show the proper weave pattern for tubing installation.  I would also keep the plates 1" apart on end and at least 1/4" from the sides of the joist bay. Don't let the plates touch the framing.
• Member Posts: 3,086
I Don't Design Differently

You can take the Alpha, Wilo or whichever ECM pump and the curve rides pretty much the same as the others I mentioned. No matter if you are using 1/2" or 3/8" the pump can overcome the head and deliver the btu's required whether a variable or fixed speed pump.

Do you really feel there is a significant savings using a ECM pump whether your using 3/8" or 1/2"? How many watts to move 1gpm @ 3ft of head if using 1/2" vs 1gpm @ 4ft or even 5ft of head using 3/8"?

I don't design differently. It's the choice the installer makes.
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
• Member Posts: 212
Floor warming

As I said earlier, is floor warming. 2 pipes er bay, with plates, 140 degree water from a Honeywell AM101 mixing valve, controled by a Tekmar setpoint controller, with a floor sensor. Done. All this engenerring regarding warming a tile floor in a bath? Really?
• Member Posts: 29

Paul,

Thank you, I appreciate you taking the time to provide some useful information. I had downloaded the Uponor Joist Trak™ Heat-Transfer Panel Installation Handbook several weeks ago, but it did not provide answers to the questions I have been asking here.

The Uponor installation handbook states you can space the Joist Trak panels 1/4” to 5” apart and my drawing in my first post has them spaced 1” apart. I changed the separation to 2” a few days ago after watching a video from Uponor recommending 2” separation.

I understand your point about spacing the Joist Trak 1/4” from the joist to avoid sinking heat away from the floor. I can do this in most of the bays, but taking off another 1/2” total in the 9-3/4” bay will make the already tight turning radius too tight. In the Uponor video linked above and the Uponor video linked below the Joist Trak is installed right against the joists.

• Member Posts: 29
RE: Floor warming

Greg,

You are misreading my posts. I am just asking questions about good installation practices for radiant PEX using Joist Trak. No engineering, just proper ways to route and secure radiant PEX in tight situations with obstructions. I could not find answers to my question in the manufacturers installation manuals and thought this site would be a good place to ask.

I think I will try again and start a new thread restating my questions.
• Member Posts: 5,839
Over kill versus over engineering...

I think what everyone is trying to tell you, is that you are not installing a "floor warming" or "floor conditioning" system, rather you are installing a distribution system with the ability to completely heat the space. Kudos to you for doing the right thing, but if your only intent was to knock the chill off the floor, you are driving a tack with a sledge hammer...

But so be it, as I said above, nothing wrong with driving tacks with sledge hammers, provided that the blow is a controlled blow. Otherwise, it will be UNCOMFORTABLY warm in the space.

Speaking competitively, if a consumer approached me and asked for a floor warming or floor conditioning system, I probably wouldn't have included plates in the mix just to knock the chill off of the floor. I think THAT is what everyone is trying to tell you...

ME
It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
• Member Posts: 5,839
80% reduction in pumping power...

Chris, on a one to one basis, a DC ECM motor will reduce the watt consumption by 80%. In the real world, your milage may vary, but any reduction in consumption is going to be beneficial to the end user/environment.

I am not in a position to dictate or calculate the actual savings, but trust me on this, it has been documented numerous times by people a lot sharper than I...

Eventually, over in Europe, you will NOT be able to purchase anything BUT a DC ECM powered circulator. As usual, what happens on that side of the pond will eventually work its way over here.

Even if it is a fixed speed circulator, it will HAVE to have a DC ECM motor in its operation.

One key advantage to DC ECM motors, is their ability to operate at real low RPM's. If you've never experienced it, there are some open rotor demonstrators out there where you can actually try and stop the rotor/impeller assembly. Even at its lowest speed, these wonderful little motors are POWERFUL. I tried it once with a demonstrator of one of the very first DC powered motors that Ted Lowe use to rep, and it almost peeled the skin right off my hand. I could not stop the motor.

I know I am preaching to the choir here, but I think it is worth repeating for the benefit of those who didn't know...

Every watt saved, regardless of how small, is beneficial to the environment.

ME
It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
• Member Posts: 3,086
Maybe I Wasn't Clear

My point was to get your thoughts on whether using 1/2 or 3/8 would make a significant difference in the pumps electrical usage in an ECM variable speed pump where the head difference is minimal. We are only talking a few ft (3-5) of head at the most in most applications.

I feel that using 1/2" in a joist, suspended application have no benefit other then the 50' longer loop length that is available to use. I like to see my loops lengths no longer then 220 at the most but in the real world they are generally 180-210.

Using 3/8" has advantages. Material cost and labor cost..
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
This discussion has been closed.