Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Water Heater for Slab Heat

L19
L19 Member Posts: 2
I've read back through all the posts and it seems like the pros are discouraging the use of a hot water heater as the heating source for slab heat.

I've also been told that I'd need a heat exchanger between the heater and the return manifold so the delta T would be smaller?

Sorry if this gets asked every week, but is there any advice? Detached garage application.

Thanks.

Comments

  • Water Heater

    If you have a water heater dedicated to the radiant slab, i.e. no DHW, then you don't need a HX.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    water heaters are ok

    for small loads and/or mild climates. when heating we assume they will be about 75% efficient which appears to be borne out well with those who have measured such things.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • Paul Pollets
    Paul Pollets Member Posts: 3,568
    Water Heaters are not OK!

    But they are used in some states, depending upon local codes. WA state allows water heaters as the heat source, providing they're being used for potable HW as well.  The circ pump must be bronze or SS and a timer must circulate the heating load for 20 min per day, every day. 

    The larger issue is premature failure due to increase temperatures used to heat radiators or wall convectors, or chlorine diffusion causing dezincification and fitting failure or tubing failure; and of course, exposure to Legionella bacteria or other contaminants, which are not dispursed by simply turning the pump on for 20 min. 

    WA state has seen over 40 million dollars in King County alone ( Seattle and vicinity) in lawsuits related to open system failure using water heaters as the heat source in the past 5 years.

    That being said, there is at least one gas-fired water heater that has a separate coil for the heating load, that doesn't expose the owners to bacterial contamination. 

    Homeowners should be aware of the risks and liability of using water heaters as the hydronic heat source.  Ask Mark Eatherton.  Or Dave Yates. 

    At some point the codes will address the safest requirements after the lawyers retire from the liability judgements.  You can have it cheap, but it may not be safe.
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    you're talking about open systems

    I have never heard of such major problems in a heat exchange system. not that there has never been a gummed up heat exchanger... totally possible... but it's not very common.



    water heaters are ok. but like all heat sources, they can be used improperly. You could install a boiler in an open system too, and that would be improper, but you don't say the boiler is "not ok".



    I agree open systems are "not ok" but let's not throw out practical solutions to low load situations on knee jerk reactions.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • Paul Pollets
    Paul Pollets Member Posts: 3,568
    The Problems...

    You may not hear of the problems in Maine happening on the other side of the country, but they are real and common. We are called to service open systems (using water heaters) with the various associated problems at least 3-5X per week in heating season and the call count goes higher when it drops below 30. 



    Any appliance can be installed incorrectly.  So what?  What you call a "practical solution" may not be so, considering the extent of the problems that have been exposed over the past 5-10 years.  Hardly a "knee jerk" reaction.  BTW, I'm not prone to responding that way.  I've been called as an expert witness and consultant to several of the lawsuits and/or problem projects. I'm sure what happened in the greater Seattle area can be found in other localities.  And...I never inferred that a boiler installed improperly was "OK". 

    The design/installation of low load open systems is up to the installer (or homeowner).  My company doesn't install open systems. Period.  If a customer wants one, we explain the features and benefits of closed systems, or electric mat/cabling., or as a budget item, the CombiCor option.  There are many contractors that will take the work and install the water heater with no separation between potable and non-potable.  I simply don't want the liability on the health side, or the mechanical side.
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    Paul

    Please reread what I wrote Paul. Note the phrase "heat exchange", it's an important one.



    "Water heater" does not equal "open systems".



    Open systems are bad. Water heaters are not. Water heaters are ok in mild climates/low loads. Open Systems are not.



    Your post said "water heaters are not ok". this is wrong. we agree open systems are not ok. In fact, I know a lot about what's happened in your area and I wish some more articles would be written in the technical rag circuit on this... widespread condemnation of open systems could finally result!



    second time in as many weeks we're locking horns for some reason and it seems like you're not even reading what I'm writing before you respond. I don't know what's up... either my writing has gotten a lot less clear, or your reading has. it's probably me.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    I think....

    It's not so much a matter of what you say, as it is what you didn't say, or how you couched it.



    Had you responded "Water heaters are OK if you don't use them in an open system", this conversation probably wouldn't have happened :-)





    As for gunked up heat exchangers out there, yes they do exist, and most are connected to Onix tubing.



    I'd have probably jumped in like Paul did had I seen just your post stating water heaters are OK.



    If things keep headed the direction that they are (government mandated high efficiency appliance standards) you may not be able to use water heaters as a heat source in the future...



    If the load is really that little, why mess with hydronics at all. WHy not go electric mat radiant and be done with it. No vents, no gas lines, no pumps, no water, just inexpensive (initial costs) comfy radiant.



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • L19
    L19 Member Posts: 2
    L19

    Thanks for the responses. I should have made it clear that it was a closed system. Enough heat to keep it around 45.

    Here's another question: I was going to staple the tubing to the insulation and pour a 4" slab, but I've read that the optimum place for the tubes are 2" from the surface. How do people feel about that? I'm thinking of running it over small squares of 2" insulation so the tubing runs up and down along its path... Opinions?

    Thanks.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    Maybe you should consider an alternate surface..

    Like the ceiling or walls. Both make an excellent radiant heat source.



    In my 30+ years of doing radiant, I have NEVER seen the tubes in the "ideal" position, and these systems work just fine.



    But, if all you are doing is trying to keep the chill off, and you want the system to respond quickly when you want to warm it up, my recommendation would be to NOT use high mass radiant floors. It will take a day or so to warm it up, versus hours with a low mass radiant ceiling.



    In my professional opinion, walls and ceilings are THE most overlooked opportunities out there.



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    walls and ceilings are THE most overlooked opportunities

    In John Siegenthaler's book, Modern Hydronic Heating, he shows in Figure 10-1 a radiant ceiling panel using copper tubing. This was in the ceiling. From the context of the description, this may have been designed by (or at least inspired by) Frank Lloyd Wright and built in the late 1940s or early 1950s.



    So radiant heating in ceilings was not always overlooked.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    Not then, but now...

    Radiant ceilings were more popular than radiant floors at one point of time back in the thirty's and 40's.



    We can "blame" our current radiant floor revolution on one person, that person being Richard Trethewey and This Old House.



    I often wonder what it would be like today if he had shown up with the large roll of tubing on his shoulders and said, "We're going to do a radiant ceiling and radiant wall today..."



    In my home in the hills, when the ceiling is on, the floors are comfortable enough to walk around in bare feet. Slightly above neutral in feeling.



    The only disadvantage I can find, if there is one, is the shadow effect created by kitchen/dining tables, and that is only a factor when when the cabin is coming out of s deep sleep. Once all surrounding mass is charged, the areas below the table feel fine.



    Today, everyone is so focused on "radiant floors", that they have a tendency to lose the concept of "radiant comfort" regardless of the energy emitter. Remember cast iron radiators? And the comfort the THEY can deliver?



    Radiant floors have been oversold in my humble opinion. Don't get me wrong, I LOVE the radiant floors in my life, but with the advent of ultra efficient homes, radiant floors are a waste of time and money. They will never be warm enough to even notice, and if that's the case, why bother.



    Just stirring the pot :-)



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Gordy
    Gordy Member Posts: 9,537
    edited March 2010
    Ceiling believer

     Agree with Mark 100 percent! 

    I have radiant ceilings from the 50's still making me cozy today. Like Mark said Quick response time, Even heat ceiling to floor, Plus you dont have to worry about floor covers, and furnishings decreasing your output like you do with the RFH.





    I Have RFH in certain rooms basement,kitchen,dining, three season porch. Some of those have both, a radiant sandwich.





    Kinda wondering if you had a two car garage with all that iron it may take a while from cold start with RFH, With ceiling you might get away with not having to run it as much.. Depends on your functions in the garage 

    Gordy
  • MikeG
    MikeG Member Posts: 169
    Putting it in the ceiling

    I am considering putting radiant in a utility room ceiling.  I have some ¾” copper buried in stone fill under the concrete slab floor, no real design on it, but I am not counting on that long term.  The ceiling is the only real unobstructed space.  It is currently open 2x10 ceiling/floor joists.  Part of the area above is a bathroom.  Is there a preferred type of plate to use, thin or extruded since it will have a drywall covering.  I have looked at the typical designs, and will most likely use ¾” plywood strips to fur out he ceiling.  Has anyone experienced any streaking or drywall movement in these installations, since oftentimes the entire ceiling is not used.  This could potentially cause uneven movement.  Heat loss is 3500 btuh using the Slant Fin program.  The slab and stone fill is insulated under and perimeter with 2” extruded foam.  I could do a floor over pour but this looks like a better alternative on all fronts.  I’m just trying to get the best advice to plan and install it now while it is open.  Thanks in advance.  MikeG
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    My suggestion....

    is to use a material called Roth Panel. http://www.roth-usa.com/usa/pdf/5A_RadiantPanelManual-Sep04.pdf



    I used this on my mountain home, which see's frequent temperature changes, and I have had no issues with sheetrock creep so far.



    It is designed for 1/2' PEX tubing.



    How large is your laundry room sq. ft. wise?



    I'd also suggest the use of a non electric thermostatic radiator valve. Proportional control.



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    Roth is good

    but at least 4x the cost of a light plate, PAP, and strapping detail. I am not convinced performance is enough better in this application to warrant the trade up.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    I guess if you don't value your labor....

    You COULD do it for cheaper, but I wanted THE UTMOST efficient (thermal wise) emitter I could get, and for the money, Roth panel filled the bill. Remember, I am tying this into solar thermal, GSHP thermal and wood gasification.



    BTW, my labor is valued at between a buck and a quarter and 3 large ones (testimony) per hour...



    The skilled craftsman in me would probably enjoy doing the wood work etc, but the economics in me tells me my time is best spent doing other things.



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    out here

    ceilings are already strapped. so the additional labor is very nearly zero. with proper insulation above, I would wager you don't see much more than a 5 or 10 degree water temp difference.



    but we'll see, over the next few years, in our new test lab shop :D
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • MikeG
    MikeG Member Posts: 169
    Putting it in the Ceiling

    The room is 12x15.  The rest of the house is 3/4" copper BB on three separate loops with separate grundfos circs.  I replace the old boiler with a modcon Munchkin and indirect DHW.  The DHW is just another zone with circ.  Piped P/S off the boiler. I did provide for additional expansion with another set of isolation pump flanges and other capped stubs.  I run the existing copper in the floor now with a three way mixing valve and grunfos circ as a separate zone.  What is the piping and control stategy to use a TRV?   Anything to reduce a pump, simplify installation and control.  Thanks  MikeG
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    Your best bet...

    Set a 3 way non electric tempering valve set for around 120 degree discharge. Downstream of that, put in a Grundfos Alpha. In the actual room, set the non electric thermostatic radiator control valve, and there you have it, a modulating radiant ceiling system.



    The only pitfalls would be minimal energy consumption, even during non heating periods, and the possibility, that all other zones are satisfied, except the one in the laundry room.



    HTH



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • MikeG
    MikeG Member Posts: 169
    Easy to change

    Mark,

    I may look at setting it up that way.  This is in my own house.  Pretty much everything else has been “old school”, oversized boiler, series loop BB zones all with one pump, uneven heat.  I’ve replaced the boiler and am now running lower temp water in the BB.  I won’t hit a design day now, so I am trying to get better control on the temps, closed the dampers and removed some fins.  It’s an old well insulated farmhouse on a crawl so pretty much most of the perimeter is BB.  I don’t really want to get into redesigning that. The crawl space gives meaning to the word crawl.  The utility room is open and easy to do what I want.  As you indicated this zone will be dependent on the other zones running and having hot water in the P/S system.  Are TRVs generally better suited for constant circ and manifold systems?  Right now it has its own tstat and can fire the boiler and zone circ, but that is all easily changed.   I do use a wood stove now and then and looking at our current way we live, the I may not have that heat in the system, but I am setting it up for long term when I no longer will be able to go out and cut wood.  Thanks  MikeG
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    TRV's are a European invention....

    The land of constant circ and outdoor reset.



    It is tough to have combination systems (bang bang and TRV with constant circ), so you might be better off sticking with the current control scheme.



    You could optimize the system by adding a 3 way motorized valve, but if you can't do anything for protecting the boiler, you might as well stick to the basics (3 way non electric, individual circ, etc)



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • MikeG
    MikeG Member Posts: 169
    The boiler is a modcon

    I have replaced the boiler with a mod con with ODR so boiler protection on return temps are not an issue.  I am trying to run lower temps in the BB and it has been OK.  The problem is I didn't get all the other projects completed in time to hit some extended design temps or close to that this winter season.  I will have to do the fine tuning next season heating season.  With the old boiler at 180 deg water the amount of BB was way too much, so over the years I removed fins, closed dampers, reduced flow etc., the poor mans ODR.  With the newer boiler I may be OK with the amount of BB with some fine tuning.  I know that combination systems are a lot harder to control.  I'm just looking to do something different and better to increase the comfort on a total system as the opportunity presents arises.  Thanks for all the insight.   MikeG
  • cpw
    cpw Member Posts: 3
    Open Systems

    I hear and read from many about the risks involved in Open Systems.  What I've read is that the risk comes from water stagnating and bacteria growing in the pex.  Several Open System designs that i have seen claim to prevent this problem by including a check valve which flushes out the heating tubing every time the domestic water is turned on.  If this stagnation is indeed the source of the problem wouldn't this check valve eliminate the risk of Open Systems?  Or are there other problems?
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    no.

    stagnation can occur in domestic systems as well. but when it does, it occurs in a system that has very little biofilm area, compared to a radiant system.



    plus, bacterial amplification is not the only problem with open radiant. summertime condensation, local water quality, present and future desire or need for glycol (grandma gets sick and you have to leave the home for a few months some year) are also major concerns of freshwater systems.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    While you were gone on vacation for two weeks......

    Legionella and his cousin from Pontiac were having an orgy in your pipes. They've been there all along, but when you went away, and quit flushing out their party hall, they EXPLODED, and had a bazillion kids.



    Now that you've come home from vacation, and hopped into the shower, you just exposed yourself to an extremely high count of airborne bacteria which you inhale into your lungs. If your immune system happens to be depressed because of all the sick people on your airplane, or smoking, or excessive alcohol consumption, you have a fairly high chance of contracting bacterial pneumonia. Now, who in their right mind would WANT to expose themselves and their loved ones to the real possibility of contracting this deadly disease?



    I didn't think so.



    At present, there is no fool, key word fool, proof way of making an open heating system safe. It is touted as an inexpensive way for people to enjoy the benefits of hydronic radiant heat.



    Let it be known that I disagree strongly with the use :-o (GASP)



    Been there, contracted that and wouldn't wish it on my worst enemy.



    Signed,



    A lucky survivor.



    Mark Eatherton



    If you think we're yanking your chain for the sake of a boiler sale, I am aware of numerous other people who have also contracted this deadly disease from open radiant heating systems. It needs to be BANNED off the face of the planet.



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    edited April 2010
    It depends....

    As I stated in this same thread, the elevation of the tube dictates slab acceleration time. If you are going to keep it at a constant, it will only be a potential issue on initial start up. Once you have the mass charged, and are maintaining it, it shouldn't be noticeable.



    Regarding the use of a heat exchanger to shorten the delta T, delta T is dictated by the pump sizing, not the heat source. I wouldn't worry about the alleged need of heat exchanger.



    I can tell you from personal experience, that even on structural steel slabs, where there were "chairs" used to hold the tubing in an elevated condition, that upon further investigation, (don't ask) the tubing was NOT found to be in the middle to upper portions of the slab as one would think. A lot of it has to do with the fact that the people placing and finishing the cement will trample the tube, and the tube itself is quite flexible. Personally, I wouldn't worry about it. Just make certain the tube gets completely surrounded by cement.



    I can also tell you that in California, the building inspectors do NOT want to see the tubing tied directly to any re-enforcement steel, because it affects the concretes ability to bond to the supporting rebar structures. It is accepted to cross at a right angle, but not acceptable to tie it in right next to the rebar. This from a practiced Californification builder.



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Paul Pollets
    Paul Pollets Member Posts: 3,568
    Changing the status quo

    So I must ask, why doesn't the RPA take a stand and amend their "Installation Standards" in regards to the use of open systems using water heaters?
  • Paul Pollets
    Paul Pollets Member Posts: 3,568
    edited April 2010
    duplicate

     
  • cpw
    cpw Member Posts: 3
    Open Systems?

    So I hear from Rob that there is a lot more surface area in radiant systems than in domestic water for bacteria to grow.  That makes sense.  I still don't have a sense of how high the risk is.  Why would certain governing boards such as the ICC approve these systems?  Are some Open Systems safe and other's not?
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    I have no idea how high it is either

    but it doesn't really matter. With all the other issues, it hit "why chance it" long before I had to quantify the bacterial risk.



    it's a relatively cheap, one time insurance policy for you, your home, and your heating system. There aren't any really compelling reasons to avoid it other than first cost... efficiency hit is negligible, additional power usage of an injection pump is negligible, and every other "benefit" of these systems is similarly "negligible".



    so on a first case basis, I say, "definitely worth it".
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    They did Paul...

    If you read the current "guidelines", there is a notification at the beginning of the section on water heaters that tells contractors and consumers about the issues surrounding the use of water heaters in direct applications, and the potential hazards attached to its use. Getting this statement in there was like pulling teeth out of an angry alligator. I actually sat on the water heater committee and wrote a proposal outlawing it, and was badly smitten about the head and shoulders by the then director, and opposing manufacturers. I asked that the question be placed before the general membership for their input to no avail. I think they knew what the outcome would have been. An informal poll indicated that most members were against the use of water heaters in a direct application. It came down to a committee vote, and they overcame us by one vote, that one vote being the second vote to come from one manufacturers rep agency. Dirty politics. Immediately thereafter, they changed the rules allowing only one vote from each entity involved. Had we known what their game plan was, we could have shut them down completely. So much for politics...



    It was then and unfortunately, currently still is an accepted method under the two prevailing plumbing/mechanical codes.



    The disclaimer was their peace offering.



    After that beating, Dave Yates and I approached the code authorities in an effort to get things changed on a national level. After two tries, we caved in and gave up. No support from inside or outside. It is still not perceived to be an issue. To quote one water heater manufacturer who has a significant amount of sway with the code legislative actions, "Show us the bodies"...



    I got my lifetime share of politics through that process, and am not interested in going through it again. All we can do is educate the public and hope that they can see the light.



    It might be worthwhile to attempt to get changes again if you are interested in getting involved, but I have no interest in beating the horse. It has enough wounds from me and Dave already. :-)



    That's my story, and I'm sticking to it.



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • cpw
    cpw Member Posts: 3
    non-oxygen barrier pex and the prestige excellence

    I'm the guy you guys convinced not to go w/an open system.  I had already, however bought my system except for the heat source and installed my slab manifolds and laid out and covered my regular pex w/concrete.  (It was a slab on slab installation).  Since deciding to close my system based on my research I'm thinking about using a Prestige Excellence for a heat source, buying an air separator, expansion tank, etc.  Is this heat source compatible w/my pex?  If not, what are my options?  A Combi water heater, or two heat sources?  What are your suggestions?  Thanks!
  • Paul Pollets
    Paul Pollets Member Posts: 3,568
    edited May 2010
    Separation

    I'd use the Taco X-Block to separate the system, unless a Combicor is used.  The Combicor doesn't modulate... you''ll need a potable expansion tank on the system side, or the O2 will burn a hole through an Extrol tank.
  • Unknown
    edited May 2010
    Radiant floors and fan coils don't know where the water comes from...

    I am a ModCon zealot but some people can't afford them.









    "The man who tells the truth, should have one foot in the stirrup.



    MA
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    if you can't afford a mod/con

    you can't afford a polaris either. pricey.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
This discussion has been closed.