Joist trak radiant tube length in last bay

gchristman

I'm installing my first radiant floor system using 1/2 inch tubing and Joist Trak plates. I purchased a 1000 foot roll of tubing and cut it into 5 200' pieces. While running my loops, I'm finding there is either extra or not enough tubing to complete the final bay. I'm able to complete 5 bays but end up with enough tubing left over to complete half the 6th bay.

My question is what do you do? Do you complete the 5th bay and cut the remaining creating a shorter loop and undesirable waste or do you complete half the 6th bay and finish it up on the next loop?

If you were to finish it up on the 2nd loop, would it be desirable to go to the end of the 7th bay come back up the 6th bay halfway meeting the hose from the 1st loop and go back down the 6th bay where you would then come back up the 7th bay?

I'm trying to keep loops even while minimizing tubing waist and extra loops, any help would be appreciated.

Bob Bona_4

Without design data we don't know how critical your loop lengths are, and if you have the luxury of extending a loop. Floor loading dictates that.

3/8" would be much easier to work btw. Shorter loop lengths but again, the radiant design is your blueprint.

gchristman

I have 23 bays each around 16' with 9 foot ceilings and 4 3x5 windows. I'm running the joist trak 8inchs on center like the documentation describes with the half inch line. Also what do you mean by floor loading?

ChrisJ

Floor loading meaning floor material, throw rugs, furniture, clothes, beds etc.

gchristman

Ok, 3/4 advantech, 1/4 hardy board, with porcelain wood style tile and occasional throw rugs with with no rubber. Second floor, so bedrooms, laundry room, a couple baths and a second living room.

I'm assuming this is a common issue?

Harvey Ramer

One would typically use the tubing off of the thousand foot roll without precut ting it into sections. The tubing should be marked every 3 feet so you can keep track of your installed length.

I'm afraid you are in a position where you will either waste a lot of tubing or have to make coupling connections in the floor.

With 1/2" tubing you can run up to 300' in a typical application. I prefer to stay around 250'. Having each loop the same length is good practice but with modern radiant manifolds that have balancing valves and flow meters, it is not critical.

gchristman

Ok well fortunately out of my 1000ft roll, I actually only cut 1 loop to 200' which was in the design spec, so would you recommend coupling that run and for the remaining joist to get it back to the header? Or would you try and couple it enough to get close to the 250ft mark and then continue on with approximately 250ft runs? I'm assuming you are marking Somewheres after the 200ft mark? Thanks.

Harvey Ramer

The tubing should have the feet already marked on it every 3'.

What kind of design spec do you have? Was the layout designed by a professional? If so, that would be the person to ask.

When I design a system I shoot for a loop length that is determined by the load and desired system hydraulic curve. In a joist bay installation, in variably, some are a little over and some a little under.

gchristman

I just have the heat loss and some basic info from the professional. He suggested 200ft runs with 1/2 joist trak. The prob is he's the local supplier and his material prices are about 6k higher than supplyhouse, so without buying the product from him, I feel bad asking him this info. He figured 200ft runs using 1/2 joist trak. The home is around 3200sq and I plan to heat all of it with radiant. So in a but shell, I'm doing most on my own.

Harvey Ramer

May have been worth the extra dough to have it proffessionally installed.

What kind of tubing are you using. Also what kind of Joist track plates, Uponor?

ChrisJ

Harvey Ramer said:

May have been worth the extra dough to have it proffessionally installed.



What kind of tubing are you using. Also what kind of Joist track plates, Uponor?

I'll do a lot.
Run gas pipe, install a steam boiler etc.

But if I was installing radiant, I'd probably hire a professional. It's just too involved and too many things could go wrong that would make me wish I was dead.

Harvey Ramer

The thing about Radiant heating is, it's not as easy as just running pipes. You are essentially engineering and manufacturing a site built heat exchanger that interacts directly with occupants. If one has any inkling of thermodynamics, the complexity and attention to detail that must go into designing the system is quite obvious.

gchristman

Uponor heat exchanger plates and mr pex grade a tubing. If I could find someone reasonably priced to design the system, I would gladly pay them, but I'd like to install it myself.

CMadatMe

If you have a complete set of prints, be more then happy to design and quote you on the material.

Mark Eatherton

The math is fairly simple and straight forward, but you already cut up your tubing, making it tougher on yourself. As others have noted, it's IS rocket science...

The math goes as follows (for the benefit of those who don't know but need to.

Based on what I can gather, your room is 35' X 16'.

You are installing at 8" on center, so the basic conversion factor is 12 divided by 8 = 1.5 linear feet per square foot of space served. To this "factor" you want to add .10 feet to compensate for all the return bends. The number you get will NOT include the active tail pieces to get from the manifold and back...

So, 35 X 16 = 560 square feet. This multiple times the 1.6 factor says you need 896 linear feet of tubing just to fill the grid. If you assumed (incorrectly) a maximum length of 250 feet per circuit (including tail pieces) then you'd divide 896 by 250 and that equals 3.58 loops. That .58 loop is the killer of the deal, so you jump up to the next whole number, being 4, which then says each in floor circuit would be 224 linear feet per circuit plus the home run tail pieces.

Industry standards say that to avoid needing to thermally balance this manifold out without having to choke flow, the maximum recommended difference in loop length would be 10% from shortest to longest.

Keeping the manifold as close to the area served is a good idea if possible, otherwise you have more math to do.

Maximum recommended length for a 1/2" circuit is 300', which if followed to the T will result in wasting 100' per roll, which is not a wise business decision, so limiting your lengths to around 250 feet works great for tube use, and also results in higher flow due to less restriction, which results in a lower fluid differential temperature, which equates to more BTUs delivered.

None of this has anything to do with the floors heating load, which should have been calculated BEFORE you got to this point. Load dictates supply water temperatures and flow rates and pressure drop, as well as the methodology of application. The methodology you have chosen is one of the best for your application.

See, it IS rocket science, but it can be done by anyone with a calculator...

We teach these things to our Radiant Proffesionals Alliance members... JOIN!

ME

gchristman

Thank you Mark, very useful information. I actually attached the floor plan of what I'm working on. I plan to heat the entire second floor with 4 radiant zones.

1. Zone 1 - Master Bdrm / bath ,
   
2. Zone 2 - Game Room, storage, laundry, hall and second bath
   
3. Zone 3 - Bedroom 1 / closet
   
4. Zone 4 - Bedroom 2 / closet
   

I'm currently working on Zone 2 which I calculated to be approximately 653 sf excluding stairs. So using your math of 1.6 I come up with approximately 1044.8 excluding some return runs. So if I divided that up by 5 loops, I end up with around 209' each plus returns.

The closet in the upper right corner of the game room right side wall is where I'm installing the zone 2 manifold, there is a chase below allowing me to get through the 1st floor and to the mechanics room in the basement. Now this might not be an ideal location for the bath load considering the distance, so I'm open to recommendations.

I did not cut all my hoses to 200', only 1 which I've concluded was a mistake, I could either replace the hose or couple it, which ever is recommended. If coupling, what style of fitting is recommended? I have own the compression ring tool, but not the expander tool. Thanks in advance.

SWEI

Cut the tubing back to the point where the coupling ends up in the last return loop (between two plates.) F1807 (copper crimp ring) PEX fittings will work fine.

gchristman

excellent thank you.

hot_rod

Circuit length within 10% of one another are fine. There is a simple way to "thread" pex in joist bays so the next loop starts up where the first ends, even mid bay. Certainly take the offer from Chris to help with some numbers.

Get a clear plan before you keep on tubing.

gchristman

I've reached out to him. Thanks. Is there a trick to compensate for the supply and return lengths of the tubing? Example, my farthest loop adds an extra 20/30 feet to the length of the loop.

Rich_49

You will compensate for that in the valve turns when the system is commissioned .