Lets start from the top on this

Ken_40

Right and left, without a schematic to visualize, is difficult at best, and impossible at worst.

I don't recall you mentioning the dual MF tees on ALL emitters! Given that the approx equivalent length, a single MF tee imparts, is ~12' of pipe/tubing, the resistence to flow is cumulative, challenging the circulator. That is not typically the real problem. What happens usually, is the dT (drop in temperature from the first to last emitter) becomes excessive, and the typical design basis of a 20 degree dT becomes whacked to 30 or 40 or in your case: "iffy flow at all."

Bottom line? You already switched the circ. and are pumping away (from the PONPC [the expansion tank tie-in point] and have bled the system of all air). You have left cooler return, at the circuit balancing plug-cock, wide open. And, have throttled the warmer of the two closed, to a near equal return water temp as felt by hand?

And, at that point, without doing anything else still have emitters that are dead nuts cold - with absolutely no warm water even at the supply riser connector?

If so, you have gone as far as possible with what you have.

Choices if that is so?:

Change the circulator and use a higher head replacement.

Split the cooler trunk again, making three plug cocks available for tweaking.

Air contamination in MF systems is legendary. Are you absolutely certain the purging component (be it the boiler block - which is the best place, or the purger fitting with the vent on top) are working properly? That the system pressure is adequate for the vertical height of the home? And, each emitter has been bled of all air possible?

If teh answer to all those pre-conditions is yes, done, the circulater or pipe design needs to be fixed.

Whattaya think?

Gronski Plumbing and Heating

Lets start from the top on this

Ok everyone, My threads on the radiant heating issue on the 1954 house is giving me more replies that seem to be all over the place and my head is swooming,I am going to break this down one step at a time,You can go and read my First initial thread for some input on the situtaion that I posted on Yesterday 10/21/2006, and Dan Ive read everything you have sent me, but its not showing me clearly what i want to determine to start to find a solution to correct this problem, if at all it can be corrected, the piping is not like the schematics as shown on the information you sent, so here goes my first question.

If I was to walk into this house right now, with no boiler in place at all, and I saw an 1 1/4" pipe coming out of the floor all buy its self, and then saw 6 1" black iron lines with globe valves coming out of the floor, tied into an 1 1/4" header,no drains, gauges, or anything else on them, what is the supply line for this system, and what is considered the return line?

Steve

Ken_40

I already answered that

look at your thread again!

I even posted it twice.

Robert O'Brien

Ken's reply said it all better than I could

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Weezbo

There is no way you know how the boiler...

that was first installed behaved. you cannot divine it by guess and by golly or even on the word of the home owner.

in this instance you have to get the known ...and deal from there.

i know it is frustrating to frick with a cluster and it makes your work more difficult than it needs to be...many many systems that "Worked" never function that lousey after you do your work.

the reason is is that you would rather make it work to its optimum... you already know the way things were never were...

there is a german word Ruck blik spiegiel it means rear view mirror dont drive forward guiding yourself by the rear view mirror. focus on what you know. the same advise is good for me too i have work to dial in today . have a hydronic habby day.

Gronski Plumbing and Heating

Hey Ken,so if i am reading this right, the Supply is the 1 1/4" pipe going into the floor, and the return is the 1 1/4" header feeding the 6 1" lines with the globe valves going into the floor, correct?

Robert O'Brien

You said you had a 45 Delta T. The cooler of the 2 is the return

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Gronski Plumbing and Heating

Again thank you for the response, read my question again,and tell me what is the supply and what is the return in your opinion,I dont care about water temps right now... I just need to know if the new boiler was tied into the two loops that i explained in the thread, properly, I know how it was tied in, but i am not sure if it was tied in properly, till i know what was the supply and return. Thanks again

[Deleted User]

Long running supply manifold...

Common place on these old radiant systems. The main supply pipe goe sito the floor 1-1/4" and there are branches (6 obviously) that take off of the 1-1/4". The mani get smaller in pipe size as branches come off, with the main eventuall reducing to 1" at the last branch. All branch circuits then do their thing as radiant floor heating circuits, then make a home run back to the mechancial room where they are brought back through valves for purposes of being able to perform a proper purge job, and if necessary, balancing act.

In other words, there are a WHOLE bunch of branch joints that you can not see underneath the concrete floor on the supply main. It's piped right by old standards. In fact, other than not performing joints within a poured slab, it's piped right by my companies standards today. We do long running manifolds on the supply and returns all day long. No home run systems allowed. Too labor and material intensive for our tastes. The zone valves are out in the system, and not in the mechanical room, but we place them in places where (hopefully) future access is not impeded by imovable objects.

ME

Ken_40

Steve,

which one of the, now five threads are you staying with?

This one for a change?

Okay. The boiler supply goes into the floor as a single 1-1/4" pipe, therefore also making that, the system supply as well.

The multiple pipes coming out of the floor, each piped to a single 1-1/4" and each having a globe valve, is/are the returns, and shoul go to the boiler's return inlet tapping. If that is how it's piped, it is fundamentally correct - as is.

However, it should have a by-pass pipe arrangement too. Based on your input so far, it appears it does not have that additional piping. This, may lead to the destruction of the boiler over a few years. The reason? A call for heat will have all the water pass through the boiler, forcing it to run for long, long periods before getting above 140F, at which point the condensation that will occur, would be at a high enough temperature to make it leave the boiler "naturally" - as opposed to condensing inside (as in: below 140F), and rusting to death.

A little internal condensing is normal and harmless. Lots of condensing going on however, creates a freakin' rain forest inside and the boiler (a naturally occuring event when anything that burns oil-based fuels runs "cool" - look at your truck's tail-pipe on a cool day: drip city) will kill the boiler in a few years - and void the warranty!
Gabeesh?

DanHolohan

Here's the drawing

that I asked you to take a look at in the Library. Notice how the manifold with the balancing (globe) valves is labeled the return.

Ken_40

Yes!

That's correct.

Gronski Plumbing and Heating

1st question is answered

Thank you to everyone on this thread and all the other threads on this situation. Everyone one on this thread is in common agreement that the single 1 1/4" pipe coming thru the floor is the supply, and The 6 1" loops with the 1" globe valves,coming thru the floor connecting to the 1 1/4" pipe is the return. now that this has been established I will post a thread entitled "Starting from the top Part 2"

Ken_40

YOUR NEXT POST GOES HERE :

Under THIS post.

The one that says STOP, is DOA

Jeff Lawrence_25

52 year old house

North east of me has that EXACT layout as you spell out in the first paragraph.

The Wall is amazing, this is what I've been looking at for a few days in pictures, trying to figure out.

I love this place..........

tom_49

Gronski,

Stop creating more threads. Its tough to follow.

bovide_4

gotta love Ken

these threads are like hitting your head against the wall, it feels so good when you stop.

Gronski Plumbing and Heating

so whats the next answer?

Ok guys, Thanks again for the first question, so now I have another question: A) The new boiler that was installed by the oil company was piped as follows; The boiler inlet,return or what ever you want to call it, is piped into what you all determined to be the system supply, or the single 1 1/4" pipe coming out of the floor. The Boiler outlet, supply or what eever you want to call it is piped into what you all determined is to be the system return header,(the 6 1" pipes coming out of the floor tieing into an 1 1/4" line. The line piped from the boiler outlet or supply is piped in 1" copper, to the system return header, with the Taco 007 pumping away from the boiler, into the system return, and there is an air scoop on this line as well, with the circulator downstream of it. How should this be repiped, and alot of you stated I needed a system bypass as well, so what size should that be as well?

Gronski Plumbing and Heating

so whats the next answer?

Ok guys, Thanks again for the first question, so now I have another question: A) The new boiler that was installed by the oil company was piped as follows; The boiler inlet,return or what ever you want to call it, is piped into what you all determined to be the system supply, or the single 1 1/4" pipe coming out of the floor. The Boiler outlet, supply or what eever you want to call it is piped into what you all determined is to be the system return header,(the 6 1" pipes coming out of the floor tieing into an 1 1/4" line. The line piped from the boiler outlet or supply is piped in 1" copper, to the system return header, with the Taco 007 pumping away from the boiler, into the system return, and there is an air scoop on this line as well, with the circulator downstream of it. How should this be repiped, and alot of you stated I needed a system bypass as well, so what size should that be as well?

tom_49

Try piping in according to Ted's diagram in another thread( which one, I forget).

Pri/sec. no bypass needed.

Ted_9

diagram

Here it is. Its not specific to your needs, but you can start from it.

Disclaimer: I found that diagram from someone else here on the Wall.

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[Deleted User]

Does it really matter???

Ideally, the warmest water should be taken to the outside walls where the coldest temperatures would be seen. But I have witnessed more than my share of systems where the warmest fluid was introduced into the interior sections of the room first, and unless you were rolling around on the floor naked, I don't think you could tell the difference overall.

Unless you can prove one way or another what the original piping layout was, and whether or not the hottest supplies were in fact introduced to the outside walls first, I don't think it matters one iota as it pertains to the general overall comfort conditions within the conditioned space. And it DARNED sure won't make any difference on the run times of the system, except that by delivering the hottest water to the interior, where your thermostats are typically located, it might shut them down a wee bit earlier than the alternate method, but we're talking minutes difference, not days...

Whats all the fuss about? If you had flow sensitive equipment, like zone valves or check valves or flow valves, I could see an issue, but if you had those things, you'd have come to us with a COMPLETELY different set of problems, like no heat anywhere...except in the boiler...

I still stand by my recommendation to use an ESBE/Danfoss THermic valve. It is the least expensive option, which is what you should do due to the fact that the HO plans on moving into their new palace soon, and it does the job of protectng the boiler MUCH better than a simple bypass would do.

Copy and paste this into your browser and go there and see the application.

http://www.danfossheating.com/products/pdf/TV_ thermic valve.pdf

Or, click on the attachment on the bottom of this thread to see the whole enchilada, smothered in green chili.

K.I.S.S. and stop stressing over the oil companies actions. They just went in there with boiler replacement glasses on, not system upgrade glasses... You're looking for trouble, and if you keep looking hard enough, you might just find it, but then its going to cost the consumer BIG time bucks, which takes money away from their other future project. Do the minimum required, and move on to bigger and better things. Live an learn, and the next time someone throws you to the 1954 wolves (hey, that homes one year younger than me!) you'll know what to expect and know how to do it right the first time.

ME (Hydronic Geezer)

Ken_40

Too confusing!

Nice drawing, too confusing.

I will make a drawing of how to pipe it in a few. By 10:30 this morning, it will be on the site near this post.

Forget about a purger. W/M has a boiler point that is better than anything you can buy or install.

This is a simple drawing, works perfectly and will make the system do what the oil company planned on; namely, to work and work well!

Gimme a few... I'll be back.

Ken_40

HERE'S THE SCHEMATIC!

If you are unsure of any abbreviations used, ask.

Please note the layout as follows:

All water passes through the 007, and the radiant panels thereby assuring full flow, and making panel manifold valve adjustments quick to respond to your tweaks and digital thermometer "ray gun" readings. Within one hour from a cool start, you will have dialed-in all the manifold cocks to within 90% of desired settings.

Here's the protocol to adjust the return manifold cocks, as well as related details:

1) Make sure the system has been off for the preceding 2 hours or more.

2) Make sure all radiant panels have been purged of all dirt. sludge and air. This is accomlished by closing all the manifold cocks except one, and purging by opening, and closing, various valves shown in the schematic to do so. When the isolated one has run clear, clean water for at least 2 minutes, close it and open the second one alone. Repeat for each manifold cock as the first. (Try and keep the water presure on the boiler between 20 and 25# during this purging. More will blow the SRV, less will allow sludge to stay behind.)

3) After cleaning all floor panels as outlined, open the air vent cap and allow the boiler block to bleed, alow the PRV to establish 12# and fire the boiler for the first time.

4) Make all the water go through the boiler (bypass closed), and after 15 minutes, read the temp of each radiant return. Leave the coolest one wide open. Close the rest to 1/2 closed. Wait another 10 minutes while boiler tries to "catch up" and read all returns again. Continue tweaking all under the principal that you want them all as cool as the wide open coldest. As they all begin to rise and after an hour tops, you should have all of them within a few degrees of each other. The coolest is ALWAYS wide open, the rest are balanced to THAT one only!

5) Set the operating aquastat to 160. If, on the coldest day of the year the house is cool, crank the aquastat up to whatever is required. 190 out, 170 back is NOT OUT-OF-BOUNDS on this design.

6) If the aquastat has an adjustable differential, set it to 20F

7) Because of the 1-1/4" system trunk, the 3/4" boiler S & R pipe size, and the 1" bypass piping, roughly 60% of the water will want to bypass the boiler and just circulate. The 40% passing through the boiler what puts heat into the floor, as long as the 'stat calls.

8) Under no circumstances should BOTH flow determining ball valves be throttled. I would start with both wide open. If after 1-hour from a cold/cool (~60F slab), the boiler water is at or below 140F, I would close the boiler bypass valve to half-way open (a 45 degree rotation of the lever). If within 10 more minutes the boiler thermometer is not at 140+, I'd close that bypass a tad more.

9) The correct final position of the two ball valves is where the "art" of YOUR job comes in.

This may appear hard. It is in fact one of the sweetest installs imaginable. It is assumed you are capable of knowing a few more fitings and valves are needed, or at worst, desireable, but this is THE way to do this alteration. I'd estimate the fix and cure at around six hours, not including travel time, learning curves or trips to the shop/wholesaler.

TSP-ing the system, additional controls, piping, fancy schmantzy purgers, bleeders etc. will not make the system work any better. I like an isolation valve on the air vent tapping W/M puts on all their boilers, so I can use the cheapest air vent available. When it goes south, close the BV and replace it in 5 years. Just make sure while your purging, bleeding etc., the air vent cap or service vale to it is closed. No sense allowing system junk from toasting a new vent with minute system junk/contamination and air bubbles. You'll be full-flow purging water and air through the entire system (first, one at a time panel blow-outs) via the boiler drain cock atop the supply outlet with a garden hose laying out the door. DON'T bleed the system in the toilet or tub. The system sludge is very staining - should some remain/

Questions? Fire away!

PS. When you reply, don't forget to check the "Notify me by e-mail about all..." check box. When anyone writes regarding this thread, you'll get an automatic e-mail in your regular e-mail inbox, with the link to this thread, automatically!

[Deleted User]

Questions/comments...

Ken, It would appear to me that what you have done is provide protection for the radiant panels, but no protection for the boiler from long term condensation production. No??

I thought the goal was to provide protection for the boiler first, and let the floors do what they may with the temperature they would see. No??

ME

Tony_23

I see what he's doing

He's restricting the flow thru the boiler and not the floor. The boiler HAS to get hotter than the floor, faster.

[Deleted User]

Yeah but...

the boiler is STILL going to see long term low entering water temperatures which WILL cause condensing, which is what I thought we wanted to avoid to increase the life expectancy of the non condensing appliance.

In my book, this bypass protects the floors from seeing too high a water temperature, but does nothing to protect the appliance. In the realm of simplicity, you can get one or the other, but not both (boiler protection AND radiant panel protection) In my estimation, the boiler protection bypass would come of just down stream of the pump, and plug back in just before the system return to the boiler.

That way you are blending hotter water with the systems cooler return water, therby raising the boilers inlet temperature and decreasing the amount of time the boiler is condensing.

Restricting flow through the boiler may increase the delta T across the boiler, but what does it do to protect the boiler from long term condensing issues? Plus, if you increase the delta T across the boiler by doing this, aren't you exposing the boiler to a large stress factor?

Curious minds want to be clarified...

ME (hydronic geezer at large)

[Deleted User]

Burnham recommendation

See attachment.

ME

[Deleted User]

Weil-McLain recommendations

Attached.

ME

Ken_40

You forgott all the relevant points:

It has to be easy, inexpensive, work, and correct what's there.

This is NOT a new install. It's an alteration to correct miriad problems already in place.

Point by point, only because it's you Mark (;-o)

1) The concept is NOT to protect the floor. The floor was running at 180 before, and may need all of that now. If you've never seen a slab Levittown house, you will find it difficult to understand why. For now, trust me. 180 may be required on a DD.

2) All c.i. boilers take 180 out and 70 back. Look at any boiler with a d/h/w/ coil. Boiler's 180. System is ambient.

3) The valve arrangement which allows slowing either the bypass water-flow OR, the boiler flow, allows infinite adjustment to minimize boiler condensation, which BTW has little to do with water temps and EVERYTHING to do with combustion by-products flue gas temperature! We tend to forget that!

4) The boiler is easily twice what's needed, meaning, condensation will be zip-squat after the very first fire-up in fall.

5) Unless you've seen how easy it is to make the over-sized boiler get flue gasses into the 140+ range by simple tweaking of the boiler bypass, you are worrying about a problem that is not present.

6) The KISS system of this piping array is evident. The condensing boiler issues non-existent. The cost of purgers, bypass operators, flow reductions in the system, condensing concerns are all put aside with this design.

And Mark? Even if this WAS a new install, I would lean towards simplicity and known infinite adjustment over exotic control evey day, every job - WHEN POSSIBLE. As long as the system is not compromised in any way (and this one is most certainly not) I think the economy of operation will be outstanding, the comfort unquestionably as good as it can be, and boiler life never compromised a bit. Remember, ALL boilers condense on start up - whether designed to or not!

As well, W/M SUGGESTS a bypass, IF condensation is a problem. It is an option, not a mandate. And, we've spoken top W/M engineering on this very design. As long as you, or I are doing the boiler bypass valve settings, they said it's okay to do it the way I drew it (;-o)

[Deleted User]

Ken...

I am not here to intimidate or prove others wrong. I'm only here to have a good time, and hopefully educate people in the process. If and when I see misinformation be handed out, I will hold my hand up and say "'SCUSE ME!!"I will aslo be the first to stand up nad say "I WAS WRONG" if in fact I was wrong. Bottom line, I guess we'll just have to agree to disagree and let it go at that.

Let the students look at the three different methodologies presented and let them make up their own minds.

But I will stand by my contention that your method provides cooler water temperatures to the radiant panel, but does nothing to protect the boiler from the real possibility of condensation production, which is detrimental to the boiler.

My preferred methodology is to use the Danfoss ESBE Thermic. I've gone back and looked at jobs where we had a great potential for condensation production where the Thermic was applied, and found the inside of the boiler to look as good as the day it was commisioned.

Have also gone back to jobs that were done with the valved bypass, which was our SOP prior to discovering the Thermic and saw substantial signs of condensation corrosion, hence the reasoning behind my actions.

Sincerely, and in the spirit of public education!!

ME

Gronski Plumbing and Heating

Understand why I get frustrated?

I see a well respected and well renown people in this industry such as Dan, who has come up with some shematics of the system piping done in the 50's, and Mark who has obtained and supplied me with informitve information and diagrams, being challanged by a guy who at this point, I dont know what he alledgely knows, or what his credentials are, that humiliates me like Im a moron in email and on this site or anyone on this site because I or they do not grasp your concepts, over Mark and Dans, and you wonder why I am confused on on which way to turn on this matter. Maybe you should look at not complicating the issue more than it is and resounding yourself to be some kind of hydronic guru or something. I am thinking 21st century technology and how it is applied today, not 50 years ago. I have made up my mind to have the boiler repiped to what has been the system supply and return, and have the Danfoss shock valve installed. Again Thank you very much to all that contributed to this Thread, Especially Mark for the time and effort you put into it as well as Dan. Mark, can I have your email so I can deal with you directly if I ever have an issue that I need some guidance on or any other questions pertaining to this issue?
With all due respect
Steven Gronski

ralman

I am confused too.

I have read that the boiler bypass and system bypass piping BOTH serve to protect the boiler from flue gas condensation. The difference between the two is that the boiler bypass lowers the supply temperature to the system. A system bypass is used when there are large water content systems connected to the boiler. A boiler bypass is used to lower the supply temp to a radiant panel. I had just moved my circulator to pump away from the PONPC and piped in a system bypass which I felt would protect the boiler from flue gas condensation and raise the average water temperature going out to the system. Take a look at the attached boiler manual, page 9, contains an explanation and drawing of the two methods. I think it is incorrect. It specifically states not to use a boiler bypass for a radiant panel system. Use it for high water content systems only. What do you think about this boiler manual?

Jamie_5

condensation

Why I think Ken's system will work:

If I understand correctly, the aim is to avoid condensation on the fire side of the heat exchanger surface caused by flue gasses, which contain large amounts of water vapor, striking too cold a surface. If that's true, it is the surface temperature of the block that needs to be controlled, and maintaining a high return water temperature is just one way of doing it. By restricting the mass of the cold water that can return to the boiler, Ken is restricting the rate at which heat can migrate from the block into the return water. That should, in turn, keep the block from becoming too cool. Hence, no condensation.

Am I missing something important?

Constantin

Both advocates make good points...

Kens approach is a very simple method that is unlikely to go wrong, unless you change the boiler temperature. Marks approach is a bit more expensive and adds one more component to the system that can fail. Yet, given a choice I would opt for the valve approch for a couple of reasons.

For one, the thermal valve should give the user more flexibility of where to set boiler vs. heating circuit temperature. I imagine that a rigid bypass is a lot like a rigid mixing valve, probably only right part of the year.

Plus, with the thermic valve in place, the boiler can run a potentially wider set of temperatures, making it a good candidate for an outdoor reset controller. Ditto for the heating loop. OR not only has a proven track record of lowering fuel bills, it also increases comfort by reducing temperature swings, expansion noises, etc.

Lastly, the thermic valve approach works no matter what is later changed in the system. The bypass approach assumes that the next installer will have the same smarts in designing the expanded system to still work with the near-boiler-piping. I would not bank on that.

Constantin

I think the manual makes sense..

... the primary-secondary approach allows you to decouple the boiler from the heating system loop. That way, if the system needs water in the 90's and the boiler needs to stay above 140°F, both can be happy. The boiler pump can act as a quasi-injection mixing system, while the bypasses afford some protection.

I presume the reason the manual does not want you to use the boiler bypass method in radiant systems is that you may end up cooking the radiant system.

Ken_40

Jamie,

You have stated the obvious far better than I.

We have serviced everything we sell and install; and have done so for well over 30-years. Being able to see the physical results of the bypass method we used on so many radiant heat slab homes in immeditae neighborhoods such as our own, affords a great opportunity to witness failure and success.

The KISS method I drew the schematic for above is bulletproof. It is so because once the bypass valve(s) are set, the handles removed and the temperatures set for optimum panel flow, coupled with proper boiler water supply temperatures, the boilers have shown no internal rust, and burner racks are free of scale drop-out in all instances.

We did not design this KISS method of bypass and radiant. General Electric did some 50+ years ago. It's in their radiant boiler design and installation manual. Their boilers were steel, not cast iron. We still have many of these boilers purring away with that exact same KISS piping design running and running well. THEY ARE ALL ~55 YEARS OLD AND STILL RUNNING WITHOUT ANY EVIDENCE OF SCALING OR CONDENSING ISSUES!

ralman

Ken, I have questions.

I feel that your schematic will work as you stated. I believe it is a boiler bypass as opposed to a system bypass. Am I correct? If so, why did you not use a system bypass as your previous post states that the floor can operate at 180* temps?

ralman

I am still confused.

Why bypass a pri-sec piping arrangement? And, Figure 7 and the description below it contradicts all the other material I have read. A boiler bypass lowers system supply temperature. But that is not what this manual is saying.

Dave Yates (GrandPAH)_1

mixing into 1954 era radiant systems

My company installed many of the black-iron-embedded-in-concrete systems we continue to service today. When they ain't broke, we let em ride Clyde. The local architect that promoted radiant was involved with Levittown's project and observed a copy-cat development where copper-in-concrete was utilized (almost all long gone now). Jeck decided he liked the less stressful black iron/concrete application. His drawings are a thing of beauty to behold.

But, he did not send 180-degree water surging through the concrete floors! Instead, he utilized outdoor reset mix for the floors, but a full temp loop for the boiler remained. Might be why many are still in use today - with their 1940's-era boilers in tact.

We've changed out a few of the older cast iron beasties in Jack's homes, but we also upgrade the near boiler piping. Where cast iron resides, we include boiler protection that's a sure thing. KISS can spell KILL when it's misapplied and 180F water coursing through a concrete floor doesn't cut it in my book for any residental radiant application - with the possible exception of ceiling-embedded radiant & even then, a system that requires 180F is poorly designed and will not be economical to operate and those temps will damage the ceiling. But that's just my opinion and the way I do things. If I were not familiar with hydronics and read this thread, I'd hire ME and trust his resolution, which has been backed up with documented information instead of bluster.

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Ken_40

Well...

It's both a system AND boiler bypass, which is why it is so useful and maximizes options and settings.

Let's just call it a bypass - period.

Hopefully THAT answer, also answers the second part of your question? If not, consider the dynamics. The floor weighs thousands of pounds. The dirt below, since there is no insulation under the slab in the vast majority of this genre home, adds incredibly high start-up loading. Imagine the inirtial start run-time just to get the floor and dirt below up to a temperature that will overcome the first 50 degree day impact on indoor temperature.

Now add foam underlayment and a decent carpet to the concrete floor. Unless waiting two days for the heating system to respond is acceptable, we need high temp water to get a reasonable response time, and comfort during the heating season.

These Lvettown and similar time-frame constructed homes with in situ steel and copper tubing were very comfy. But to offset window and insulkation factors, never mind the floor covering(s), very high water temps are required. The slab and tubing have handled high temps since being installed without any degradation. Any leaks or failures resulted from lack of re-enforcement within the slab (meaning, no wire or re-bar was used in these homes.) A monolithic pour was done on the sometimes compacted dirt on grade. After years of "settleing, tree root "stress-wedges" working the perimiter of these pours, cracks developed which resulted from huge shearing forces at play. Virtually all radiant slab homes from the 50's and until recently were subject to these forces, until we started putting re-enforcing steel in the pour.

Hair-line floor cracks are the death knell for any tubing in a floor; be it C, Steel, rubber or plastics. Re-bar reduces or eliminates that potential, which is why we no longer just pour concrete slabs without re-enforcement.

Does that address your concern?