Joist heating model

Tim Doran_2

Here is a thermal model of a joist application using 4" spacing. The underfloor insulation is an R-15 and the subfloor and finished floor are an R-1.25. The water temperature average is about 123f. Everything is shown in metric units because thats what our program does. I am hoping for an upgrade to become available soon. The surface temp works out to be about 76-77f which is 22-24 btu/sqft with a 65 degree room set point.

Tim D.

Earthfire

spacing

how do the supply & surface temps compare to a 8"extruded plate installation? Is tighter spacing a viable alternative to plates? If it is how soon for the ADS upgrade

Tim Doran_2

Nope

I posted this as part of an ongoing discussion regarding joist heating. In my opinion direct staple up with tighter spacing is not a viable alternative to extruded plates at 6 or 8 inches on center and I feel that this is substantiated by the low surface temps achieved here. We will try to model the plates when we have a chance.

Tim D.

Boilerpro_3

Tim D

Are you using your HePex or Onix? I was looking at Onix in diret sontact with the subfloor in my application. Did't know anyone did staple up with Pex anymore due to squeaks.

Boilerpro

DaveGateway

more pex

Tim,
It looks like the joist are 16"OC?
16" / 3 = 5-1/3" average OC across a floor.
Try 6 runs in each 16" & it would still cost 1/2 as much as high quality heat transfer plates & 2 runs of pex!!!!
My point is, "more bang per buck"
BP

bill clinton_3

very interesting

Seems to me you could match plates with say 155 degrees. To my eyes, this supports the use of suspended tube.

Bill

ALH_3

less pex

I think 1/2 the price might be an exaggeration. With proper tools and methods I'll make an educated guess that it would take 1/2 the time to install plates and one loop of pex versus 3 loops without plates. Once the plates are installed the tubing goes in very quickly. Fewer loops means fewer manifolds, fewer connections, and drilling fewer holes. Drilling fewer holes means less structural degradation of the floor joists. Fewer connections means fewer potential leaks. Additionally all the staple-up problems still exist. Calculating the actual cost goes far beyond material costs.

DaveGateway

more pex

ALH,
I agree with you on some of your points & disagree on others! 1/2 the price (including labor) might be an exaggeration, I think it would be closer to 1/3 the price!
1/2 the time to install plates??????? I think you have this one backwards!
I agree with your points: Fewer loops means fewer manifolds, fewer connections, But the way I pull the PEX, it don't require ANY more holes! What are "all the staple-up problems"? BTW, I don't like staples either, I use the plastic electrical C clamps mentioned in Dans' book.
BP

Tim Doran_2

Pipe

This is based on a fairly genaric "pipe" as indicated in the program therefore this model is actually performing better than pex or epdm. It has a coefficient close to copper. BP you are correct, we do not do direct staple up with pex any longer.

Bill, I am not sure that six runs of tubing vs two runs with plates would be a viable option considering labor but I guess its possible. Someone once said that anything under 4"oc reached a point of saturation and a significantly decreased return on investment. Wish I could remember where I saw that.

Tim D.

Tim Doran_2

Plates

Actually, plates at 8" oc would only require an average water temperature of 105 to get the same output as the suspended model that I have shown. They would also provide the 45 btu/sqft that started this whole discussion at 152/153.

Tim D.

DaveGateway

more pex

Tim,
The diminishing return principal applies to about everything!
I would like to see the simulation or IR photos of 6 runs / 16"
Just because "Someone once said" something, you know where I'm going here.
BP

Boilerpro_3

Contact area

> This is based on a fairly genaric "pipe" as

> indicated in the program therefore this model is

> actually performing better than pex or epdm. It

> has a coefficient close to copper. BP you are

> correct, we do not do direct staple up with pex

> any longer.

>

> Bill, I am not sure that six runs

> of tubing vs two runs with plates would be a

> viable option considering labor but I guess its

> possible. Someone once said that anything under

> 4"oc reached a point of saturation and a

> significantly decreased return on investment.

> Wish I could remember where I saw that.

>

> Tim

> D.

Boilerpro_3

Contact area differences

The contact area between EPDM and the floor is much greater than with stiffer tubes like copper or pex since it is compressed slightly during installation. HR says its about 1/4 inch. or so. I would suspect that despite the higher insulating value of the tubing wall, this very tight contact area would do a lot better job of conducting heat to the floor than just hanging the tube. Since the EPDM tends to have some give it probably makes extremely good contact with the floor...probably alot better than plates since the plates wont conform to the floor surface.

I can't imagine what a pain it would be to install Pex 4 inches OC. Definitely plates would be easier despite the intensive labor needed for installation.

Take a look at HR's infared photos from a few days ago showing EPDM staple up, pex and extruded plates, and hung tube at 8 inches OC. It looks like the plates have about twice as much output as the EPDM, so doubling up the top probably will equal the plates output. This was after only 6 hours of on time, might change some if the time frame was longer.

Boilerpro

bill clinton_3

More info

Tim: I really appreciate the information you are putting out here. I've been forced to work on seat of the pants guesses. Reading between the lines, it seems you're convinced using plates is the thing to do and I'm not going to try to persuade you otherwise. Still, I would dearly like to know what performance your model predicts with two and three suspended naked tubes in a standard 16" oc joist bay running average 155 degree water temp. Sure would make me feel better to know the answer to that question. Thanks.

Bill

Tim Doran_2

Contact

I used to install a fair amount of Heatway product in the early days of my career and I know that it had good contact where the staples were and that it tended to sag a bit between so that it was no longer flattened againt the sub floor where they were not. I guess that if you staple it real close together it could be that it all has the theoretical 1/4" contact. That still only works out to 12 square inches of contact per four tubes per lineal foot of joist bay. Most extruded plates are 4" wide and provide 60% tube contact or higher ( Dale Picard is a good one to comment on this) which with a 1/2" tube equals over one inch of direct tube to aluminum contact. Spread the heat over 96 square inches of aluminum per lineal foot of joist bay and there can be little left to question.

So it seems that we could go on like this for days and it seems that it is becomming more of a disagreement than a discussion which is unfortunate. It also seems that you are more interested in discrediting me and/or Wirsbo than you are in sharing for the benefit of all who choose to read this which is also unfortunate. I have shared the facts as I know them and with the intent that we may all benefit from open exchanges of information.

I replied to your original post for two basic reasons.

1- because you incorrectly stated that a Wirsbo system could not deliver 45btu/sqft and that our software would not accomodate this design. If you are going to make incorrect statements like this I am obligated to set the record straight. We now know that a Wirsbo system can be designed to provide 45 btu/sqft and that our software will accomodate this design. We also now know that what happens above the bottom of the subfloor remaines constant and can not be efected by the type or brand of product applying the heat. The differences are all below the subfloor.

2- because I was concerned that you had an error or some problem in your calculations that was going to cause you to put in a system that may not perform to expectations regardless of what products you choose. I have given this due diligence and shown what I believe to be the correct result of such an application. Nuff said.

I am not trying to discredit a competitor( I have great respect for Dr. kilkis and the tech crew at Heatway) or you or anyone else and I am not saying that plates are better than staple up. There are times when plates are required or are a better choice for certain applications. There is a time and a place for everything and this was the time and place for me to offer plates as the Wirsbo solution to 45btu/sqft.

Tim D.

Boilerpro_3

My apoligies, Tim

if I appeared to be becoming combative. That absolutely was not my intention. I also appreciate your concerns about this design because I have them too. Few people would show the concern you did when someone is talking about using someone else's products in a way that may not work. Most would just shake thier head.

I am trying to figure out why there are such great discrepancies between two good company's heat output calculations. I suspect the Watts program may be a little overly optimistic, while the ADS delivers more conservative data. Just don't know.

I have revisited the design in the ADS and in the Watts program and still cannot find a descrepancy. I am still am only above to get about 36 Btu/sq ft with a 86F surface temp with a room temp of 68F. Average water temp was about 130. I did notice that ADS uses a higher R-value for tile, so I suspect that would increase the water temp over the Watts. I also changed the load in the Watts program from window load to infiltration to hopefully take out the potential influence of cold surfaces, and the output remained the same.... something fishy appears to be going on.

At what conditions were you getting 45 btu/sq ft? Maybe I can work backwards and find out whats going on in this design.


As always, respectfully,


Dave Bunnell

hr

The contact patch with rubber

In my experience I have seen a lot more under stapled rubber, than over stapled. In other words more often the staple is not driven enough! So the tube is not in direct contact with the floor even at the staple! So that contact patch could not be 100% for the entire loop. This is important if you want conduction transfer.

Air pressure, the way the gun is held against the hose, knots or hard spots in the wood, weak stapler, etc. Are all valid concerns with direct staple up.

Personally, I feel the ONLY tube that should be stapled directly to the subfloor is the Onix. Any other product will move, be noisy, and create some wear points. It's only a matter of time.

Unless of course you still have some solaroll in your stash

We used to go around with a 2X4 stud and tap the staples to assure contact was good. Also the staples need to be no more than a foot apart, imo. The Onix is stiffer than the early Entran, which did in fact droop between staples when run hot.

Then again I have seen over stapled rubber also, where the hose is pinched below the staple restricting flow.

A fine line in EPDM staple up, not too much staple, not too little, and tight enough spacing. If you are using this product be sure you are aware of the "connection"

hot rod

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Boilerpro_3

Yep,

> In my experience I have seen a lot more under

> stapled rubber, than over stapled. In other

> words more often the staple is not driven enough!

> So the tube is not in direct contact with the

> floor even at the staple! So that contact patch

> could not be 100% for the entire loop. This is

> important if you want conduction transfer.

>

> Air

> pressure, the way the gun is held against the

> hose, knots or hard spots in the wood, weak

> stapler, etc. Are all valid concerns with direct

> staple up.

>

> Personally, I feel the ONLY tube

> that should be stapled directly to the subfloor

> is the Onix. Any other product will move, be

> noisy, and create some wear points. It's only a

> matter of time.

>

> Unless of course you still

> have some solaroll in your stash

>

> We used to

> go around with a 2X4 stud and tap the staples to

> assure contact was good. Also the staples need

> to be no more than a foot apart, imo. The Onix

> is stiffer than the early Entran, which did in

> fact droop between staples when run hot.

>

> Then

> again I have seen over stapled rubber also, where

> the hose is pinched below the staple restricting

> flow.

>

> A fine line in EPDM staple up, not too

> much staple, not too little, and tight enough

> spacing. If you are using this product be sure

> you are aware of the "connection"

>

> hot

> rod

>

> _A

> HREF="http://www.heatinghelp.com/getListed.cfm?id=

> 144&Step=30"_To Learn More About This

> Professional, Click Here to Visit Their Ad in

> "Find A Professional"_/A_



it's been a few years since I've used Onix, but I think they recommend 8inches OC max for staples. My few Onix installs so far have been under 100 year old floors, so knots, etc. have to be watched out for. I am looking at it now because I have a floor full of screwtips sticking out. That stuff is pretty nice to zig zag around such obstructions.

Boilerpro_3

Yep,

it's been a few years since I've used Onix, but I think they recommend 8inches OC max for staples. My few Onix installs so far have been under 100 year old floors, so knots, etc. have to be watched out for. I am looking at it now because I have a floor full of screwtips sticking out. That stuff is pretty nice to zig zag around such obstructions.

BP

Tim Doran_2

Sorry

If I took things wrong Dave and if I was out of line at all. I guess that my next question would be how are you trying to get to 45 btu/sqft? In other words are you trying to get the heatloss to this point or are you trying to design to an existing 45 btu/sqft heatloss? To get there in either case you will need to work from a 65 degree room set point or lower as your surface temp will be 87.5 at 65 and even though OSHA says that is ok it is pretty warm. The floor covering R-value and underfloor insulation will play a big role in the final water temps requied.