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Why can this not be done?

Chris Burt
Chris Burt Member Posts: 19
First off I live in Central Minnesota. I have a single natural gas 94,000 btu water heater in an open loop system. The system currently heats my 20'x 30' garage which is a very well insulated. The walls are made out of Insulated concrete forms, the 6" thick slab has 2" of R-10 rigid foam under it, and the garage doors are insulated. The insulation in the ceiling of the garage was blown in to be a value of R-50. The heat has not turned on in the garage yet. I keep the temp set at about 50°F in the garage. I would like to use the same heater to also heat an additional bedroom upstairs. The bedroom is going to have a have a hardwood floor. Now the problem seems to be the hardwood floor needs to run at 140°F. That is way to hot for the domestic hot water. I would have to add a mixing valve. Then I still need to be able to heat the cement in the garage floor and I don't need water that hot in that floor another mixing valve. Could I put extra tubing under the hardwood floor say 1/2" Alumipex at 6" on center then run the temperature lower around 110°F? My train of thought is this would give the needed btu at a lower temperature. Then have the water return through the garage floor. This would have the hotter water running through the wood floor. The cooler water running through the cement floor. Even if the return water was at 71°F the temperature of the room, it would still heat the garage just fine. Am I nuts or is this possible ?


  • kevin
    kevin Member Posts: 420
    have you..

    done a full heat loss? Run seperate zones to each area at the proper temps. and spacing according to the heat loss calcs. Don't make those runs of tubing too long. May I ask why you are running a open system? Bacteria is a real issue and risk. If the price for a boiler is an issue seriously consider having 2 water heaters.kpc
  • Chris Burt
    Chris Burt Member Posts: 19

    I have one small heater that hangs on the wall and is power vented out the wall. It does a good job of heating domestic water and has heated the garage, porch, and laundry room very well. I do not want to add another boiler and more venting if what I have works. I guess my reason would be that a water heater is a very under utilized piece of equipment. It sits for probably 23 hours per day doing nothing. If I get a second heater it is going to sit 6 months of the year doing nothing. While the heater sitting next to it will sit for 23 hours doing nothing. As for the heat loss calulation the contractors ask about the square footage over the phone nothing about insulation, windows, ETC and say I need pipe at 12" on center @ 140°F. If I ask about using more tubing at a lower temperature all I hear is a silence over the phone and I am told to run higher temperatures and less tubing. What is wrong with more tubing and a lower heat? Won't you still get the same amount of btu's? I am looking at three runs of 250' basically dividing the room into threee parts. Bacteria has not been a problem yet. I use one of the return manifold outlets to suplly water to my toilet so I get plenty of fresh water in the system.
  • Dave_4
    Dave_4 Member Posts: 1,405
    wood floors etc.etc

    -isn't max temp into a hardwood flr about 95 deg F?....
    -never seen an 'open' heating system, but if you use a domestic water heater it's probably ok...
    -dumping heated water into the toilet sounds like a waste of energy, even if it's 70 deg
  • Dave Yates (PAH)
    Dave Yates (PAH) Member Posts: 2,162
    If you built it, they will come.

    A water heater sitting idle for six months is infinately preferrable to you being idle 6' under the lawn for ever. Isolate the two fluids and use some simple mixing strategies. And just for the record, 140 degrees is just about right for domestic hot water. The point of use mixing valves are not needed until you get to within a few feet of the bathing module & at that point you can reduce the temps to 110 degrees for much safer temperatures. 120 degrees F is not the safe temp you think it is! Details appearing soon in a magazine near you(G)

    Legionella bacteria need just four things and not all need to be present for their enjoyment.

    * Water temps between 50 & 133 degrees F

    * Biofilm (found in all potable & open system piping & vessels)

    * pH between 5.0 & 8.5

    * Stagnation & for bonus points? - added volume, which your open system adds nicely.

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  • PJO
    PJO Member Posts: 140
    Well put Dave...

    Have you a bit of interest here? :-)

    PLEASE, do not continue to have this don't go outside in the middle of a big thunderstorm do you? You're chances of getting hit are actually pretty rare, but common sense stops you, right?

    You just heard a little rumble of truth from PAH...think of it as thunder.

    Just my thoughts. Take Care, PJO
  • Larry Ticknor
    Larry Ticknor Member Posts: 38
    One size fits all?

    Sounds like your contractor only knows one way to do the job. One system does not solve all problems in the radiant heating world. A good heat loss is a start to finding out how close the tubing should be and how hot the water needs to be. If you want cooler water temps look at putting the tubing on top of the subfloor with distribution plates. Knowledge is power. If your contractor doesn't know then you need to get a new contractor or set about getting your own education.

    Seriously consider the warnings about the bacteria. Having a heater sit idle for 6 months of the year is cheap insurance. No one fully understands the bacteria world and how it interacts with your body and pre-disposes you to other diseases even if the disease causing agent is not found in your water system. My wife is a microbiologist and she had one thing to say about open systems, "Not in my house and hopefully not in any house I visit."

    Larry Ticknor
  • Cosmo
    Cosmo Member Posts: 159
    This is why I beleive things are better left to proffesionals...

    This whole open system business is a sore point for me. I ran accross an open system type job in a town that was served by a municipal water distribution system. There was nothing moving in the radiant bathroom floor for months during warm weather, the water just sat there. The worst was there was no backflow preventer installed on the water main coming into the house. Just think, this DIY could have killed a lot of people....... Not to critisize, but please correct this situation with at least a brazed plate heat exchanger, pump, expansion tank, fill valve, and relief valve! You love your family don't you?

    "Plumbers Protect the Health of the Nation"

  • Dave Yates (PAH)
    Dave Yates (PAH) Member Posts: 2,162
    Thanks Cas

    Would you believe, there's a heat pump system on the market that grabs potable water from the street main, uses it to produce heat or cooling and then returns it to the main? Now that's crazy! Kinda rules out the need for backflow preventers, eh?

    Not upstream from me bubba.

    Fortunately, our local water co saw to it that these systems can't be installed here.

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  • Cosmo
    Cosmo Member Posts: 159
    Hey Dave I have a question

    Concerning what I posted above. Where I live the brazed heat exchanger is good enough to isolate potable water from non-potable water (i.e. heating loop). However I know that these heat exchangers will eventually leak. Then we rely on the fact that most potable water systems operate at atleast 40-50psi, and a leak would cause the 30psi relief on the heating loop to blow...forcing the homeowner to correct the situation. Is this enough protection? I think that is the same thing with the now popular water heaters (i.e. Bradford White Combicore) that have a heat exchager built in. Add to all this the tankless coils in boiler which have been around for eons.... Where is the backflow protection? Just thinking out loud.....
  • Cosmo
    Cosmo Member Posts: 159
    Didn't mean to single out

    Bradford White, I have been and still am selling these water heaters by choice. The same goes with all the indirect water heaters we install every day. I guess I was just wondering how we technically decide how much protection is enough....
  • Dave Yates (PAH)
    Dave Yates (PAH) Member Posts: 2,162

    a great question & one that will be addressed at the RPA convention. The short answer is "it depends".

    If we're dealing with water to water, then I'm not uncomfortable with the scenario you describe because of the difference in the two system's pressures you've cited. The concern can arise from aspiration during flow, which can siphon low pressure into high pressure. That's why a third intermediary zone (can be fluid filled for good thermal transfer) should be incorporated when exchanging Btu's between potable and chemically treated hydronic fluids.

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  • Tim R
    Tim R Member Posts: 5
    Potable water protection in open heating systems

    In our area an open heating system is approved by our local Dept of Health as long as all materials are approved for potable water and if a pump with a 365 day timer is installed in order to cycle the heating system for 1 hour per day.This is UPC country which is a fairly stringent Plumbing Code.
  • Cosmo
    Cosmo Member Posts: 159
    An old timer once told me....

    That as long as the heat exchanger is a single piece of tubing/pipe, it would be permissable.... for example a coil for a tankless hot water heater in a boiler. I guess the reason was that things are more likely to leak at a joint, so joints were'nt allowed when a cross connection thru a leak was possible on a heat exchanger. I am not sure how true this was. You hit the nail on the head with aspiration of a chemical compound thru a heat exchanger. I was going to ask that next. Thanks Dave, I will have to watch my RPA updates to see what you guys come up with at the convention.

  • Dave Yates (PAH)
    Dave Yates (PAH) Member Posts: 2,162

    Who will know when the pump fails? Got stagnation? Once a day injection of stagnated potentially bacterial laden water? No thanks.

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  • Cosmo
    Cosmo Member Posts: 159
    I'll second that

    Today I Had a late sevice call, the customer complaind that they just moved into a home and the water smells. I happened to know the previous owner and I asked him how long it has been since anyone used the water. He said that the house had been sitting empty for two years with no tenant. Of course nobody thought of emptying the water lines, and water heater...since the heat was on who cares right? It is not like something was going to freeze! Now he has a mess on his hands, just glad that nobody got sick.

  • Dave_4
    Dave_4 Member Posts: 1,405
    double wall HEXs

    ...are required in san francisco between domestic & non-potable water...
  • Royboy2
    Royboy2 Member Posts: 16
    looks like there's not much support here for open systems

    ... but I do wonder if they can be set up in such a way that makes them less hazardous in the bacterial dept. - as they seem to be systems that have the virtue of simplicity on their side. In particular, I've seen more than one suggestion of a system where a check valve forces incoming water to move through the heating loops before going to the water heater & tap - which is intended to eliminate stagnation in the non-heating season. Seems simple enough - perhaps some side effects that would need to be considered, like would there be problematic condensation on any tubes/alum fins during summer months.

    Anyone have any opinion on this approach?

    There is also the idea of regular timed circulation through the heating system year round, though that seems less elegant to me.

    Seems like any house that is left vacant for any period of time (seasonal residence, vacations) without draining plumbing would be suceptible to this bacterial hazard but I never hear of concern with this. How come?

  • Dave Yates (PAH)
    Dave Yates (PAH) Member Posts: 2,162
    another point

    I've seen examples of what you refer to. Great theory except that it ignores pressure & flow problems created by running through hundreds of feet of small diameter tubing. Scalding and extreme loss of flow as downstream or lower floor fixtures are utilized.

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  • Royboy2
    Royboy2 Member Posts: 16
    but ...

    Dave, I would assume that a group of parallel small loops in a radiant system, say three 1/2" tubes (which exceed one 3/4" tube in cross section) would not create significant pressure & flow problems. Feel free to enlighten me on this as I'm not fully up to speed on doing this sort of calculation.

    I'm still intrigued by the concept of an open system for some applications and, being new to The Wall, wondering if they are universally despised here or if this thread is just sort of anti-open-system.

  • Dave Yates (PAH)
    Dave Yates (PAH) Member Posts: 2,162
    With pleasure! Here's an article I wrote on this very subject.

    Article title - "Here's Your Sign"

    BILL ENGVALL’S song, "Here’s Your Sign," plays in my mind at times. Like
    when I see a water heater with a 3/4-in. cold water feed line and a 1/2-in.
    hot water outlet. Why do that?

    Or when I’m told that open-system, cross-connected potable-hydronic systems are so great because
    they give you free air conditioning and increase the capacity of your water heater by as much as
    50%. All of which can be done without any risk to your health because all the incoming cold water
    will be run through the radiant heating system on its way to the water heater and, therefore, prevent
    stagnation of potable water along with tempering the colder well or municipal water?

    Those were the claims made during a heated e-mail exchange in which I was told, "You just don’t
    get it!" In yet another e-mail regarding open-system construction, I was told I’m "just a dumb
    (expletive deleted) plumber." We’ll address the slam about being a plumber in another column.
    Where’s my sign?

    Aside from the potential health risks associated with open-system construction (see articles/0401/legionair.html), there’s the issue from last month’s
    column regarding pressure losses and balanced flow in plumbing systems using potable PEX water
    lines. It’s an issue ignored by many proponents of these systems, but one that exposes the customer
    to potential scalding or poor delivery pressures as downstream or lower floor fixtures are used
    simultaneously with the upstream or upper floor fixtures.

    Now before anyone gets his boxers in a bunch, let’s take a minute to examine some hard realities.
    Line lengths for 1/2-in. PEX hydronic systems are often 250 ft. Systems connected to a
    combined-use water heater will have fairly small Btuh loads in order to permit bathing without
    losing too much capacity, right? If not, they need their own dedicated heat source.

    At 250 ft. and using the chart from last month’s column, which shows a .208 pressure drop per foot
    with a 4-GPM suggested maximum flow rate, these systems are dealing with a potential 52-PSI
    drop during peak flow conditions! That’s before adding losses due to elevation changes and line
    lengths to fixtures. Here’s your sign.

    But let’s change that to heating an area with 1,000 ft. of 1/2-in. PEX using four 250-ft. loops
    attached to a manifold.

    The shower on the third floor (loss of 10.4 PSI for the change in elevation of 24 ft.) is being used by
    Mr. Jones who loves his high-flow, 8-GPM showerhead. He’s adjusted the faucet to compensate for
    that long four-way-split-run pressure loss and the differential from the lower resistance to flow in the
    cold water line. He’s using an 80%/20% mix of hot/cold because of the 55°F well water and the
    heating system, which was already running, has lowered his storage temperature.

    With 6 GPM to split between the four hydronic loops, he’s got a pressure drop of 8.5 PSI (.034
    PSI/ft. x 250 ft. @ 1.5 GPM). But wait a minute, we’re not including the 75-ft.-long run of 3/4-in.
    PEX from the water heater to Mr. J’s shower! That’s another 75 x .082 (3/4-in. PEX at 6 GPM) for
    another 6.15-PSI loss. That’s 10.4 + 8.5 + 6.15 for a total line loss of 25.05 PSI!

    If Mr. J’s pump system is set at 20/40, he’s toast. Even if it’s set up to operate at 30/50, there’s going
    to be trouble brewing the instant a lower floor or lower-resistance-to-flow fixture is used. If you were
    water, which way would you go? Here’s your sign.

    Well water systems contain higher levels of organic material than most municipal systems, which
    means greater odds for biofilm in the tubing and, therefore, more amplifiers for bacterial growth.
    Low flow in long horizontal lengths of tubing, no matter the materials used, promotes
    sedimentation and biofilm layers. Here’s your sign.

    Free air conditioning? OK, let’s introduce that 55°F well water into the 1,000 ft. of in-floor PEX
    tubing for the 15-minute duration of Mr. J’s shower. Will this chill the room appreciably? Will the
    tubing sweat if it’s installed in a staple-up underfloor application and sees humid basement air?
    Will Mr. J need to lay flat on the floor to appreciate the benefits?

    If Mr. J is on a municipal system, he won’t be getting chilled water and will likely be receiving water
    at or above his room’s air temperature during those peak air conditioning load days. Do the
    "benefits" outweigh the pressure, flow and health-related issues? Here’s your sign.

    What about the claim that such a system increases the capacity of your water heater by up to 50%?
    That assumes the floor is heated to its upper limit, the circulator is running and the water heater
    has just finished recovering to full temperature. You know what they say about the word "assume"!
    Here’s your sign.

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  • Royboy2
    Royboy2 Member Posts: 16
    do I get an assist for that question?

    Thanks, Dave for that info. I'm not yet up to speed on doing the flow & pressure calcs (though it's evidently a skill I could put to use). Any reference that would help me out on this? I'd like to calculate this out for job I'm currently looking at where the parameters are a bit more modest:

    municipal water

    10' 3/4 copper to WH

    4 250' radiant loops

    35' 3/4" and 8' 1/2" PEX to 2.5 GPM 2nd floor shower

    The link to legionaire at Contractor doesn't seem to be functional at the moment.

    Appreciating your (and everyone else's) willingness to share info here & still wondering if there is a strong opinion held in some circles that open systems can be done in a way that works.

  • Dave Yates (PAH)
    Dave Yates (PAH) Member Posts: 2,162
    An atta boy(G)

    for the lead in.

    All of the tubing manufacturers have flow and pressure charts. Some require a bit of digging to find and the various fitting types can have an affect too. Once you find their info, it's just a mathematics game.

    Proper sizing methods for copper systems are essentially ignored too.

    There are a number of people who hold very strong opinions that open systems are perfectly safe, but we're working on them! There are several internet DIY sales companies that actively promote open systems and at least one that sells tubing many here feel is sub-standard. Let the buyer beware.

    I always felt that open systems were wrong, but it wasn't until a few years ago that I had anything more than a gut feeling to go on. When you stop to think about the Legionella issues, it's only been a few years since the bugs were discovered and the knowledge keeps changing on an almost daily basis. As a result, there are a tremendous variety of opinions regarding how to deal with them and what the proper potable hot water storage, distribution and point of use temperatures should be. The ASPE convention just ended yesterday and that was one of the main topics. It will be interesting to see what changes will come out of that meeting.

    Keep in mind that the open system construction idea was brought about back when water heaters came set at much higher temps and the systems installed were copper baseboard. Low temperature systems with favorable bacteria criteria were unheard of, PEX wasn't around and Legionella had yet to be discovered. That was then, this is now.

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  • kevin
    kevin Member Posts: 420
    i can...

    uderstand the idea to want to save money up front on an open system...but does this really save money in the long run? a water heater does have a much shorter life than a boiler(have to be replaced possibly 4 to 1) and the possibility that the health risks are there. Is it really worth it? Lost time at work, feeling rotten from for a day or two from minimal exposure or God forbid death(remember very young and very old are more at risk). I could n't live w/ myself if I was even partly resposible for killin someones child. If we are in this bussiness don't we owe it to ourselves to give our customers the best possilbe value and a good feeling that we did a good job No corners cut? Just say no to open systems? kpc
  • Dave Yates (PAH)
    Dave Yates (PAH) Member Posts: 2,162
    closed systems and water heaters

    There are times when water heaters make perfect sense - providing they are closed loop systems either as stand alone or isolated via a heat exchanger. The heat emitters don't care where the Btu's come from. The jury is still out on system longevity where water heaters are utilized as stand alone with water that remains contained and constantly reused. If barrier tubing is utilized, then free oxygen is kept at bay. Under those conditions, I would expect a much lomger than normal life span.

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This discussion has been closed.