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High Temperature Under-Floor Radiant?

I have gutted a bathroom and in place of the existing hot water radiator I am considering underfloor radiant.  The cost of low temperature quik trak was high due to costs of running new loop, circulators, panels and supply lines.  Any thoughts on running high temperature radiant like Ultra-Fin using the existing radiator supply lines, and then controlling the room with non-electric control valve instead of separate loop with its own T-stat?

Comments

  • Paul Pollets
    Paul Pollets Member Posts: 3,590
    Solution

    If yon use the Oventrop Unibox, you'd be able to control the new radiant zone using the bath radiator's supply and return, without having to install additonal mixing or pumps. This presumes the radiators are piped in parallel; not in a series loop!!
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    paul

    this is the second time I've seen you refer to a unibox like it's a mixing device.



    do they sell a variant that actually mixes? If so, how does it work without a pump pulling from it?



    my understanding of the unibox that we've used, at least, is that it is only a flow regulator. so if I have 180 in a supply pipe, I would never want to to run that into, say, quik trak. mixing down would still be required.



    no?
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • Paul Pollets
    Paul Pollets Member Posts: 3,590
    UniBox

    The Unibox is an independent wall mounted mixing device that does not require a pump. It can handle up to 15K Btu load for a radiant mix, a manifold can be attached if more than 1 loop is required.  The device is made to mix high temp (radiator mains) to low temp.  It will not work on a monoflo system. It uses a TRV head for setpoint.  Any Oventrop dealer can get them.  Chris Rorke at Blueline Supply in Jackson Hole, WY. Best hydronic invention since sliced bread. 

    [url=http://www.oventrop-na.net/cutsheets/UniBoxTech.pdf]http://www.oventrop-na.net/cutsheets/UniBoxTech.pdf
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    I hope I'm not being dense

    but I think you are misunderstanding the operation of that device.



    I believe it is simply like a TRV: it regulates flow, but it does not regulate supply temperature. it has a "return temperature regulator", but I'm pretty sure it regulates return temperature only by choking back flow, so it's manipulating the temperature drop but not the supply temp.



    I am not aware of any device that would allow for 3-way mixing that would not require a pump pulling from the valve.



    I've used them on a couple of jobs now and I'm pretty sure I have that right. But it would not be the first time I was all wet on something I thought I was pretty sure of, as well. I have an email into oventrop on it just to make sure.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    heard back

    the Unibox is just a TRV, not a mixing device.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • Paul Pollets
    Paul Pollets Member Posts: 3,590
    edited February 2010
    No Misunderstanding...

    I don't think I'm misunderstanding. I have several dozen Unibox applications installed. All work perfectly, and have for years.   It is a "2 way valve" in essence, controlled by a TRV head.  It also has an internal limiter that can be adjusted to limit the output. The supply temp is reduced because the flow is reduced.  Read the link to the Oventrop page describing the device.  This is not a 3 way mixer that requires a pump.  I don't quite understand your question if you've installed these devices?? It matters less what you call it, it matters more that it does what it's supposed to do. BTW, I've at least 10 applications using a Unibox with Quick Trak or Climate Panel. Maybe they should have called it a "Flow Choker"? 
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    Paul

    the temperature coming out of the unibox is not less than the temp going in. that's what a mixing device does. that's not what this does.



    it just comes out slowly so your average temp across the loop is reduced. but that's average, not supply. fine for room temp manipulation, but there is more to the story.



    so if you have 180 degree water like a radiator or baseboard system might have, you don't want to run that into this box and then into a radiant floor zone without mixing. You will send 180 degree water to the floor. You might not overheat the room, because flow will be very low and the dt high so only a short part of the run will be 180, but that first part of the loop may not be very happy. if you're doing THAT with climate panel, I'd be surprised if you aren't seeing or hearing of any issues.



    this is no more a replacement for mixing than a TRV is. this one just has an option to control the TRV action on return water temp as well as space temp if you like.



    I'm not saying it's not a great product, it is, it just doesn't replace the need to do mixing in radiant floor applications. it can work WITH mixing, and if you don't NEED mixing, great, but if you need mixing, the unibox doesn't mix. that's all.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • Bob Gruber
    Bob Gruber Member Posts: 5
    Better (and Cheaper) HIGH TEMP Under-Floor Radiant

    Guys (Paul and Rob),

    I believe Samriles question was about HIGH TEMP radiant, such as the mentioned UltraFin, and not the merits of the Unibox and whether it mixes or not .



    Samriles,

    Sorry, but I just don't trust PEX at 170 - 190, and the last time I

    scoped out UltraFin aluminum fins, I didn't like the proximity of sharp

    aluminum fin edges to the PEX pipe.

    The best solution for heating a bathroom with HIGH TEMP radiant (140 - 190 degrees F) is not UltraFin, which uses PEX with attached aluminum fins, but the old tried and true copper fin-tube (element only) suspended about 1/4 to 1/2 down from the top of the joist bay, with as much insulation below the fins that you can fit without touching the bottom of the fins.   I have been using this method to heat bathrooms and kitchens for the last 20 years, with very satisfactory results. The floor does not over-heat because the tubing and fins are not in contact with the floor.  You are heating the joist bay air space (think mini-convection currents).   The best part is the simplicity , low material cost, and the lack of maintenance down the road compared to mixing valves and variable speed pumps.

    The non-electric control is a nice touch, but raises the head considerably. It's not really necessary if you use the right amount of fin-tube in the floor.  My formula is 3-4 times the length of baseboard given by Slant-Fin's heat-loss program.  This usually ends up being 2-4 feet of fin-tube in each sealed joist bay (don't forget to seal the ends of the joist bays with insulation).

    Also, I use long turn 3/4" copper elbows to reduce head as much as possible so the existing zone or house pump will do the job.

    IT WORKS !!!!
  • djthx
    djthx Member Posts: 52
    Joist Bay Air Space Under Floor Radiant

    Your idea of using high temp, joist bay air space (mini-convection currents) under floor radiant heating sounds interesting.  Does it matter how far under the floor the copper fin tube is suspended?  Do you take the size of the floor joists into account?  Will it work 2 x 8 joists?  In addition to heating the joist bay, you're also heating the joists themselves, which seems wasteful.   Have you considered insulating the joists themselves with foil backed foam (to prevent the joists from stealing heat? 
  • Samriles
    Samriles Member Posts: 3
    High Temp Under-floor Radiant

    Bob, I don't think the Ultra-Fin uses normal PEX, it uses a multilayer tubing that has a welded aluminum layer positioned between two layers of PEX.  That should handle the job safely enough, and would seem less expensive than the copper fin-tube you use.  The reason for the control valve is that this is a one shot deal -- once the floor goes in there won't be any access to adjust anything below as there is not access to the space under this bathroom floor. 

    And this still should be less expensive than the other suggestions, by avoiding too many bells and whistles.

    Thanks for all the suggestions and any others still to come!  Sam
  • Bob Gruber
    Bob Gruber Member Posts: 5
    Better High Temp Under-floor Radiant II

    djthx,

    I try to leave between 1/2" and 1 1/2"" between the underside of the floor and the top of the fins, and at least the same between the top of the insulation and the bottom of the fins.   Direct contact with the sub floor might over heat the floor if you are running 190 degree water.  Some air space above and below the fins allows the "mini-convection currents")  The fin-tube I use is Argo Lo-Trim 3/4" element only.  (http://www.digelair.net/pdfs/TECHLIT/ARGO/lotrim_brochure.pdf )                                   It measures 1 7/8" H and 2 1/2" wide, so in a 2 x 8 floor that leaves approx, 3 1/2 " for insulation with 1" air spaces above and below the fins. What I like about this fin tube is the reduced height, the open sides, and plastic reinforcing strips at all four corners. Since the length of fin-tube in each bay rarely exceeds 5'  -  6' , supports for the installation are simply 3/4" plastic suspension pipe clamps through the 1 1/4" holes I drill in each joist.

    If you want to get fancy, yes, you can insulate the sides of the joists with thin foil backed foam, or better yet, thin (1/2") foil-backed fiber glass (duct wrap).  Plain R11 or 13 fiberglass batts (3 1/2") with thin foil-backed fiberglass wrapped from the top of one joist to the top of the next joist is ideal.  this will still work in a 2 x 8 floor with 3/4" air spaces above and below the fins. This system works for wood floors, laminate floors, tile floors, and entire houses, as long as the customer understands they cannot put 3/4" padding and carpet on top of the sub floor.  (I have one customer who successfully put thin commercial carpet directly on the sub floor)



    Sam,

    Kitec (sandwich PEX) is better than normal PEX, but threading continuous coils of ANYTHING (except rubber tubing) through joist holes without damaging the tubing is VERY difficult. Mechanical joints for PEX that are buried under the floor are simply not acceptable to me.  Despite the high cost of copper nowadays, I feel my method is relatively inexpensive (fin tube is about $ 2.50 - $ 3.00 per ft ) and extremely reliable (with decent soldier joints)

    Concerning the non-electric control valve; it only works if the zone or whole house is calling for heat, and then, only limits the amount of heat emitted.  The real problem with most of these is they have relatively high head loss, meaning that the flow through the loop will be severely restricted when you DO want heat.  When I am replacing a single above floor cast iron radiator for a bathroom or kitchen with this system, I usually run the return end of the loop up through the floor into a vanity cabinet or wall access panel  with a full-port ball valve and manual air vent valve, then back down into the floor to connect to the existing return pipe. The manual air vent (loose-key air valve or decent boiler drain valve) is needed to bleed the loop properly.  With two ball valves and some space between them, you could try installing your control valve in this location.  Just be ready to remove it if the room doesn't end up heating properly.
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    unibox

    came up as a solution for this poster. I was saying it was not a good solution for this poster because he was asking what it would take to do low temp radiant and this would not solve that problem.



    I think high temp radiant is no worse than high temp baseboard. Suspended tube or with ultra fin should be cheaper than baseboard, and it would result in more evenly warmed floor temps in the area, and it should be MUCH easier to install than anything in copper is going to be.



    I have "baseboard radiant" in my house and it works... near the baseboard elements. but it's not that great at any distance, and by the time you fill joist cavities with all you want there, you're way over the cost of PEX. even PAP is somewhere around 0.50/ft and requires no sweat joints. Baseboard is *just a wee bit* more expensive than that.



    for no additional benefit, and only downsides.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    wait a sec

    are you seriously claiming that PAP is more difficult to install in a joist bay than BASEBOARD?



    bob... come on. this is done every day, all over the country, without splices. and with splices, it's not significantly more likely to leak than the dozens of sweat joints you're making. I have *never* seen or heard of a splice leak develop over time, though I do agree it's best to avoid if you can.



    You're more than welcome to do whatever you like and advocate for it, but let's not spread FUD while we're doing it. PEX and PAP joist installs are routine business. managing to avoid major damage while installing in a joist bay requires only basic attention to what you are doing.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
This discussion has been closed.