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converting baseboard to radiant

bauer Member Posts: 79
Hi there,

I just came across this website and have spent considerable time with all the resources offered - it is a great source of information.

I am hoping someone can help me out a bit - I know it is difficult to talk specifics through a forum, but I will paint the picture. I am currently heating a single floor, approximately 800 square foot house with a boiler and radiators. The boiler is fairly old, and is controlled by 1 thermostat with a taco circulator on the return side of the boiler.

I have demo'ed a bathroom (approximately 45sq ft) and removed the old baseboard radiator (not fin tube - old style baseboard). I've done the heat loss for the room and radiant piping --- in the form of quik track 7" -- is sufficient to heat the small space. I'd like some idea, however, as to how this can pipe into the boiler.

I know the water temp needs to be decreased through a mixing valve -- and from what I have researched I am seeing that this small amount of radiant shouldn't create water cold enough to create a condensation problem in my boiler. I want to pipe this so it is independent of the main thermostat however and just looking for some options.

would it be possible/preferable to pipe it with a zone valve & utilize the one circulator pump, or better to add a 2nd circulator. it is such a small stretch of tubing -- about 75'.

if I did have to add a 2nd circulator, wouldn't I have to relocate the original circulator off of the return side and place it on the supply side for the radiator units?

looking forward to some educational conversation


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
    There are a few more in bits of information needed.

    There are a few ways to do this. You can use a 2 way valve, 3 way mixing valve, 4 way valve,crossover bridge, primary/secondary.  Depends on what you have and some logistics.  My best advice, and not a salespitch, would be to grab a few of Dan's books--Hydronic Radiant Heating, Primary-Secondary Pumping Made Easy, Pumping Away.  Specifically "Hydronic Radiant Heating" (page 179) has exactly what you may need.  It's basically tapping into and existing baseboard loop with a secondary loop, closely spaced tees, a 3 way valve, and a circulator. You wouldn't have to worry about low temperature return water.  But you are right that you need to lower the water temperature.

    As far as relocating your existing circulator, If you draining the system and cutting into some pipe, you might as well take advantage of the opportunity to upgrade some of the components, i.e, pump away, spirovent, diaphragm expansion tank, etc.  You could upgrade the control on your boiler, to an outdoor reset.  It all depends on how much you want to do, spend, and how much control you would want.
  • bauer
    bauer Member Posts: 79
    how many circulators

    thanks for the advice, I just ordered a few of those books. What you are suggesting sounds like the first picture below, no? If so, is it true I would need a total of 3 circulators? 1 for regular baseboard units, 1 for the secondary loop, and then another after the 3-way mixing valve?

    Second question -- while the boiler isn't exceptionally old, the piping to the baseboard radiators is very... looks like 3" cast iron...huge pipes. would it a) make efficiency sense and b) work, if while upgrading system components as you suggest I also replaced these lines with 3/4" oxygen barrier pex?

    thanks again
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506

    You didn't say if you had a one pipe system or 2 pipe.  (put up a pic if you're unsure.

    The diagram and page I referenced in Dan's book seems to be exactly what you need.  When you get the book you'll see.  I just don't feel comfortable posting a diagram from an author's book without their permission.

    Based on what you described, I would use diagram 3 with some modifications.

    Note the primary circ, piped on the supply, after the compression tank.  That's going to feed your baseboard radiators.  Depending on your layout, off the primary loop, hopefully after all the rads, is where I would take off the closely spaced tees, mixing valve, circ and radiant loop. 

    Now, you say you have 3" mains, it's definately not steam?  Or converted gravity hot water system.  You may wanna post a pic of the boiler and near boiler piping before we go any further, just so were not heading down the wrong path.

    As far as replacing lines, that depends on your budget.  But if you're using oxygen barrier pex for the radiant, you don't need to worry about the other components.  If you're not, then maybe you want to isolate the radiant via a braized heat exchanger.

    I'd still like to see some pics.  The 3" mains have me concerned.
  • Greg Maxwell
    Greg Maxwell Member Posts: 212
    Bathroom radiant

    Use the KISS principle. T87 tstat, SR501 Taco relay, 007IFC pump on low speed, Honeywell AM101R mix valve. Done. Floor surface temp on a bath can be elevated to around 90 degrees (check with grout and tile mfg to make sure that doesnt cause a problem), warmer floors in a bath are preferable.
  • bauer
    bauer Member Posts: 79
    2 pipe

    it's a 2 pipe system, what I perceive as direct return. I attached a few pics, sorry if they're hard to see. I may have exaggerated their size a tad -- maybe 2"? I was assuming it was an old gravity system...the house was built in the early 1900s...that was converted over but they never changed over the original piping. I was just wondering if I was losing efficiency because of how large those iron pipes were -- if its not worth replacing them then maybe just wrapping them in some insulation?

    To explain the picture, the black or wrought or cast iron pipe -- whatever it is -- is mainly in place for the supply & return line. On the floor currently there are 3 full size radiators, and 2 baseboard radiators. I removed 1 of them that was in the bathroom. Some of these radiators are connected by way of what looks like 1" black iron pipe, some are connected to the supply/return lines by way of 3/4" copper.

    The radiant tubing is 5/16" hePEX oxygen barrier, so there should be no problem there. If need be, I can tap into the original system on any number of places - if the end of the run is best I can do that.

    thanks for your willingness to educate
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    edited July 2011
    Conservation and unintended consequences...

    Those big ol' pipes, regardless of their size, are acting like radiators in your basement. If you use that space, and you insulate it, the heat source will no longer be able to add to the comfort mix.

    It can actually be beneficial.

    During periods of low loads, it acts like a buffer tak, o someplace to park extra BTU's, and keeps the appliance from short cycling, which is NOT a good condition to have (short cycling that is..)

    I've had customers who had these big old pipes in their basements, and I had strategically placed removeable pieces of rubber pipe insulation, so that when they are assembled in the basement, they remove the insulation and the space stays reasonable. When they are gone, they put them back and the temperature drops.

    You have to be careful not to over insulate, and possibly cause potable water pipes to freeze when design conditions come.


    ps, Not sure how this end up out of sequence, but it is in response to the question about pipe insulation.

    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.
  • bauer
    bauer Member Posts: 79
    unused space

    what if the basement is purely storage? Wouldn't I save some heat by insulating those big pipes? they could still be used as btu storage as you said...

    and being a basement in the NE/Mid-Atlantic, I can't see the temp dropping below freezing without the heat from those pipes.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    Watch out for infiltration...

    that is the ONE THING that could come back to bite you on the hind side. Getting completely rid of it can also be detrimental (mold and mildew issues), but where required, if you insulate the heating pipe lines, the plumbing pipe lines may have depended on that for IT'S freeze protection.

    Other than that, it is worth while to insulate the mains.

    You could always put in some means of freeze protection, like a fan coil unit set for 35 degrees F, and cross your fingers and toes... or electric resistance heat tape.

    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.
  • bauer
    bauer Member Posts: 79

    resurrecting this old thread... since I am the OP I give myself the authority to do so.

    I'm looking to implement this system -- based on recommendations from above I've read most of Dan's writings and, since it is a small bathroom, decided to keep it simple and inexpensive and just tie into the baseboard loop with a 3-way mixing valve and a circulator pump.... no separate thermostat - I will just wire the circulator to turn on when the main pump does.

    My only main question would be what circulator would be most appropriate to use here. I'm assuming it won't be very large and that something like an 007 would be overkill. We are only looking at about 75' of 5/16" pex radiant tubing.
  • bauer
    bauer Member Posts: 79

    quick bump?
This discussion has been closed.