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Open Loop heating VS Closed Loop Heating

viccipeviccipe Member Posts: 20

Everyone has provided opinion, but unfortunately no solid proof cases recent for me to show prospects who are buying open loop systems predicated on price only.

I feel for us traditional wet heads to merely state the obvious will not win the war. We need proof. Real live cases that i can present as indisputable evidence as to why they should never go to the open loop system.

I believe the greatest minds in Hydronics are here in this community...i call upon your wisdom and experience....


  • viccipeviccipe Member Posts: 20
    Open Loop Vs Closed Loop

    Should open loop be the perferred method of radiant heat?
    Is the public really at danger?
    If so why do administrative authorities continue to except?
    Trying to get real up to speed with this controversial issue. Does anyone have feed back that can put this issue to bed?
  • Brad WhiteBrad White Member Posts: 2,440
    Paging Dr. Yates

    Legionella issues aside, why would anyone want a system with fresh oxygenated water continuously going through it? That is what I could never figure out.
  • Tom MeyerTom Meyer Member Posts: 300
    Case by case basis

    Both open and closed systems have their place in designing hydronic systems.

    Typically, we recommend closed systems because the increase in price of barrier PEX is more than offset by the cost of oxygen resistant components. On large jobs, say a warehouse, we price compare and look at other factors to decide which is less expensive on first cost, and which makes more sense in the long term.

    Sometimes not so obvious facts help us decide: the difference in circulator head for open vs. closed systems.

    Food for thought: Does it have to be ALL "Open" or ALL "Closed"? With the increased popularity of alernative fuel stoves (typically "open") are we going to be looking at more systems which are a logical mix of open and closed?

    Hmmm...I wonder.

    Tom Meyer
    Precision Hydronics Corp
  • ConstantinConstantin Member Posts: 3,782
    Lookup Mr. Yates' articles at

    (thank you, Robert, for hosting them!)

    Like Brad, I don't see the benefit of open radiant heating systems other than a lower initial outlay IF you do not spec out the appropriate equipment (i.e. bronze circulators, etc.) Once the right stuff is called for, that difference largely dissappears, as does the business model for some shady DIY suppliers.

    Given the rather minimal cost to do it right from the beginning (i.e. closed) and if I were a contractor, I would not risk the liability that an open system entails. For example, many manufacturers will void the warranty on their HX's in such conditions.

    Combining an open system with providing heat and DHW through the same pipes is pure madness IMHO. Open systems have their places, but providing heat and hot water should be done through hermetically separated systems.
  • hrhr Member Posts: 6,106
    Open isn't a problem

    As long as it is not connected to the potable water system in any way.

    Drain down and drain back solar systems are open, as are most of the outdoor wood furnaces.

    hot rod

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  • soot_seekersoot_seeker Member Posts: 228
    Combining DHW with heating in an open system

    Very short term in terms of the health of the equipment as well as the comfort and health of the occupants.
  • Dave Yates (PAH)Dave Yates (PAH) Member Posts: 2,162

    Open cross-connected potable-hydronic systems have no place anywhere, anytime, anyplace. If you believe otherwise, I invite you to provide the proof-positive. The proof that open cross-connected systems must be classified as a bacterial amplifier, on the other hand, has been demonstrated, backed-up and a ton of references have been given for researching the reality. Put up or shut up.

    Spent the last two days at Taco. They have the ultimate potable/hydronic set-up for utilizing a water heater to deliver hydronics in the industry. Safe split between the fluids. As they say: "Do it once; do it right".

    Spent time with Timmy (Timmy's Tips) today and earlier this evening as he got ready for an evening class. The man is one deep well of knowledge - his students are very lucky (IMHO).

    Stopped by's studio and got treated to the Providence $30.00 welcome wagon parking nazi's! Three minutes & thirty bucks.

    Tomorrow, we head off to visit Viessman.

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  • Tom MeyerTom Meyer Member Posts: 300
    Defining a \"Mixed\" System

    Any system that used both open and closed loops should be separated by a water to water heat exchanger. That wasn't clear before, and some may have thought I meant to mix them without the heat exchanger. They would have been absolutely right.

    Tom Meyer
    Precision Hydronics Corp
  • JimJim Member Posts: 184

    How about it voids the warranty on most heat sources intended to be used in closed loop systems only?

    IMHO why would you spend the extra money on non-ferrous components and heat exchangers to save a few pennies on tubing? Unless it was installed in error and now you are left trying to make the existing system functional.

    How about it can potentially allow system components to fail prematurely if the components are not compatible with such a system?

    Sorry, I know you want defined fire power but I just got back from a troubled system where the installer ran out of oxygen barrier tube and switched half way through to non-oxygen barrier tube. Why the switch? Wasn't money issues. The installer didn't know the difference between the two types and when it was brought to his attention it had been covered up.

    His response was "Isn't all pex the same, pex is pex, right?" I guess it seems obvious that someone else took his RPA designer test for him.
  • Paul PolletsPaul Pollets Member Posts: 3,022

    I think open systems prevail in the marketplace simply because an inexpensive water heater can be used to drive the system, instead of a boiler. The water heater costs several thousand less than even the smallest wall-hung boiler. Plus, the contractor doesn't have to install any mandatory controls like the LW cutoff, manual reset high limit or RPZ backflow device and PRV. The "low initial cost" mentality drives many decisions in the N. American heating market.

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  • JimJim Member Posts: 184

    Even if you choose to install a lesser system based on cost I wouldn't design or install a system without a LWCO and MRHL. Why would one allow their reputation, integrity and pride to be comprimised just because the mandatory controls are not required?

    I agree with you Paul about the low initial cost mentality driving decisions about such a significant investment. I also know there are many projects that utilize a water heater and they work. But sometimes you need to invest a little more money for a safer system. IMHO.

  • Paul PolletsPaul Pollets Member Posts: 3,022

    As Dan said a long time ago, or at least it seems a long time ago: "The marketplace will prevail..." Some contractors are not concerned with reputation, integrity or pride...they have a business to run and a sale is a sale. If they can do the job for less, they will. They also see an advantage in being able to provide a "lower cost system". Yes, they do have a slight advantage...their system does cost less. And it does less. Open systems may have their place in projects typically under 1000SF, but I've seen so much premature failures of these systems and very poor installation practices, I can hardily condemn their use...but it ain't up to me. BTW, some of these failed projects were designed by a mechanical engineer.

    Just for the record, in 8 years, I've installed 12 systems using a certain gas water heater with a built-in coil for radiant. 7 of the tanks have failed and been replaced. 5 of the 7 systems were closed loop with RPZ feed, 2 were open with a manual fill. All failures were coil related. That's why I sell boilers for heating applications. It's not worth it to think that the customer is gladly willing to pay an additional $XXXX to replace what was just installed a few years ago. Even though every customer was told that these applications have a short life expectancy! Go figure.

    These are choices that will only change as energy really gets pricey.

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  • JimJim Member Posts: 184
    I agree

    Thank you for putting this in perspective. Some folks are told what to expect but either they don't hear what you are saying or money is talking a wee bit louder.

    I know that you design and install quality systems with acceptional energy efficient equipment as your standard!

    I had the opportunity to meet one of your biggest fans while visiting Viessmann in Langley, BC.

    Take care.
  • hrhr Member Posts: 6,106
    A lot of the open system\"push\"

    has to do with the appliances being sold by the companies that promote dual use DHW/ radiant.

    You will often see a Polaris spec-ed out as the heat source for these online systems.

    Polaris's can only be used as open system heat sources. I've asked several times and the manufacture of that tank refuses to allow their use as a closed loop heating devise. They just don't have the listing for that use, I'm told. To use it as a closed loop hydronic heat source voids any warranty. True enough I recon.

    I visited one of the online radiant companies website recently. They claim to have sold 2500! Polaris radiant systems last year.

    Imagine how much tube, pumps, etc go along with that.

    And this is just one of a handful of online radiant suppliers. Add 'em all together and that's some big numbers.

    Probably bigger sales numbers than all the contractors here combined.

    hot rod

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  • viccipeviccipe Member Posts: 20
    Tally of responses concerning open & closed loop systems

    I guess from reading the threads it appears unless a huge class action lawsuit occurrs and is exposed nationwide it appears open loop systems will continue to become more popular.

    I aggree with everyone about the educational issue, but we all know education is a problem across the board.
    I know we won't see fresh water systems in Public Works any time soon...but else where seems fair game.

    I just don't understand how municpalities allow manufactures to sway standard plumbing engineering.

    I think everyone says pick a stand in the issue. You can lead the prospect right but prospect is gonna make the mind up based upon thier own personal characteristics.

    Was hoping someone had some real fire power stats to help me back safe closed loop systems. I thank you so many experts in overall fluid dynamics for your candor.

    best, Vic
  • Mark HuntMark Hunt Member Posts: 4,909
    And some

    lovely parting gifts are waiting for you!

    So long! Thanks for playing!

    Bye-bye now!

    Mark H

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  • I think it's pretty simple, really.

    You can use an open system with a dedicated water heater for small loads, and the efficiency hit won't kill your fuel bills. That's fine.

    For larger loads, you want a more efficient heat source. That means a closed system, end of story there. This includes most homes. Not all, but most. The Polaris is completely obsolete, so using it for larger loads is just plain stupid... you can get one of several mod/con boilers WITH a storage tank for DHW for the very close to the price of one of those suckers, and it'll be quieter, more efficient, and the whole system will be more comfortable with the cheap and easy onboard outdoor reset options. No reason to buy a finicky "condensing" water heater that you can't even run at condensing temperatures without shorting out the igniters any more. No reason at all. There is no opinion to be had about that... it's fact, given any measure you choose, the Polaris has been completely superceded in the marketplace.

    If you have a load small enough to economically use a water heater, then you can spend a small amount extra for a dedicated water heater to do it. Then you have zero concerns about constantly adding new gunk to your system (I've seen some sludge nightmares, believe me), zero concerns about additional health risks, and a small increase in cost. That's cheap insurance, if you ask me. You could add a heat exchanger too, but that could gunk up so why do it? Use a tankless for DHW, and turn off the heating tank in the summer, and you're doing pretty well overall.
  • viccipeviccipe Member Posts: 20
    NRT rob

    Really felt your sense of resolve.
    And it is true. maybe open loop is being excepted in areas of low heating necessity. since areas with real cold temperatures just can't fool around. this definetly is a line. when i moved to the west coast i realized how many apartment blds were going up with individual hot water tanks per unit for billing/metering purposes rather than central heating. so you think maybe in these 800 sq. ft. apts. maybe 1 hw tank open loop is OK.?

    COdes in west coast are allowing 5 minute run cycle a day off electronic timer as a way to satisfy safety.

    But all that tubing with street pressure running through the building. My preliminary investigations show no complaints concerning sonic velocity.

    But mostly heatloss not enough to satisfy bathers in some cases.

    I have also heard complaints about in the summer duty timer wasting heat and overheating apts.

    Many fresh water people say water in extensive plumbing systems are too always ready to develop bacteria as well.
    They have a point which is why recircualting DHWR is so important.
    I've seen some try to incorporate that into heating design as well.
    wonder if maybe good for copper towel warmers?

  • I would stay away from combined potable/heating in all cases. You don't see many plumbing systems with a 200 foot straight run, yet that's a minimum you'll see in a radiant system. That's a whole lot of home for a whole lot of fun buggies. In that case, if space is an issue, a small heat exchanger is again cheap insurance. Both for the owners, and the heating system. At least then if anything gunks up, it'll be something in the mechanical area that can be replaced, as opposed to something buried in the floor!
  • hrhr Member Posts: 6,106
    Rob, what do you mean by

    an open system with a dedicated water heater??

    In my mind an open system is one that is non pressurized and open to the atmosphere.

    So for a radiant system to be open it would have to be combined with the potable water where faucets open.

    The other type would be connections to un-pressurized, open to atmosphers wood furnaces.

    hot rod

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  • Sorry. Our "private terminology" around here is that "open" means "open to oxygen" diffusion and "freshwater" means continuous new water and connected to potable. Sometimes I forget everyone else doesn't differentiate along those same lines.

    So I have no problem with systems that are open to oxygen. I have a big problem with systems that continuously add new fresh water and move on to potable.
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