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Newbie on the block


Just to give you a little background info, I'm an hvac contractor but primarily installing residential furnaces, a/c, gas lines, etc. Over the past few years I have turned down many radiant jobs due to lack of experience or no experience for that matter. I have take a few radiant courses and have read some books just to gain some knowledge. Work has been a little slow lately and I have been offered another radiant job. It's just a basement radiant in slab job but will only be used as a secondary source of heat. I have already taken a few steps and download a free trial of loopcad and it made the following calculations

- 6 loop manifold with the longest loop being 204ft and the shortest being 114.
- 8" on centre except for the bathroom where it will be 6" on centre and 1/2 pex
- Insulation will be put under the new slab
- Bradford white combi tank will be used

This is where I might need some advice from someone. I've seen some sketches in the books I've read and from the classes I've taken but I'm not exactly sure how to build the manifold. I have a pretty good idea but I'm not sure what type of circulator pump to use and if mixing valves are needed or if a slab sensor is required.

Any help would be great. On another note I know this forum is for professionals in the industry but I'm looking at adding more to my business and my career.



  • Rich_49Rich_49 Posts: 2,540Member
    Cannot tell you if you need a mixing valve ,sensors or what type circ without you telling us Supply water temps at design , surface temp at design .

    Why are you building the manifold instead of purchasing a manufactured one? Do you think it will save you money ? It can be done but I found out a long time ago that the time it takes to build things just because you can is usually not time well spent . There are and will be some times when what you need is not manufactured , save your effort for those times .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • RobGRobG Posts: 1,850Member
    There are waaaay to many details that need to be given to get any constructive advice. We will be happy to help you. A slab install is a perfect job to get your feet wet with radiant. Have you done a heatloss to ensure the radiant will be capable of heating the slab?
  • delta Tdelta T Posts: 801Member
    Your loop lengths need to be closer in length to each other. If your longest loop is 204 and your shortest is 114 you will have problems with hot spots and cold spots because the flow will not be equally distributed between all of them. I generally try to get all of my loops to within 10% of each other on length (admitedly not always possible), though you should not have any problem as long as they are within 20% of each other. Having one loop be twice the length of another will cause problems though. Concrete slabs are generally more forgiving than other radiant applications.

    Agree with Rich, you need to know what you want as far as features go before you decide whether or not to build a manifold or buy one. Check out Caleffi, they have some pretty awesome prefabricated manifolds, as does Legend. Just depends on what you need. Usually the prebuilt one's save you money vs the time to fabricate.

    Take the time to do all the numbers up front, it will save you headaches in the long run. A proper heat loss is number one. what kind of floor covering? what is the R-value of the underslab insulation? What is the value of the slab edge insulation? make sure your boiler is not oversized for the application. Oversizing can cause just as many problems as undersizing for condensing boilers.

    If you really want to dive in head first Modern Hydronic Heating by Sigenthaler is a great book. Goes over everything you could possibly want to know about hydronic heating with an emphasis on the more modern design theory and application. I would also recommend getting your hands on the iDronics journal published by Caleffi. It is free and it is very comprehensive, you can sign up through their website to get the print version, or you can download the pdf's. They put out a new issue every six months.

    As Rob stated, we would be glad to help, but we need much more information.

    Welcome to radiant!
  • onedrivenonedriven Posts: 7Member
    Hey guys

    Thanks for all the input! It comes much appreciated. To start I think I mislead when I said I was going to build my manifold. What I meant was I wasn't sure how to put everything together (i.e does the expansion tank go after the circulator, do I need an air scoop on top of the expansion tank etc.) I was planning to buy a upanor or watts or rehau manifold or something along those lines. A supplier I go to suggested vanguard. Are they any good? To answer some of the specifics

    - Insulation under slab will be 2" equal to r-10
    - insulation on sides will be 1"

    Details on load calcs from loop cad

    Room 1
    Circuit A-1 204ft, flow .46usgpm, delta T 20, heating 24.5 btu, floor 85 degrees Fahrenheit, supplemental 17 btu

    Room 2
    Circuit A-2 114ft, flow .10 usgpm, delta T 20, heating 10.4 btu, floor 75.3 degrees Fahrenheit, supplemental 4.2 btu

    Room 3 - 2 loops
    Circuit A-3 and A-4 127ft, flow .23 usgpm, delta T 20, heating
    Heating 19.7 btu, floor 80 degrees Fahrenheit, supplemental 12.7 btu

    Room 4 - 2 loops
    Circuit A-5 144 ft, .17 usgpm, delta T 20,
    Circuit A-6 149 ft, .19 usgpm, delta T 20
    Heating 13.3 btu, floor 72.4 degrees Fahrenheit, supplemental 7.2 btu

    Do they calcs add up. I downloaded the program as a free trial and it has been quite easy to work with. Delta T you mentioned them loop lengths from room 1 and 2 are too far apart. Would it be better to combine them? Go with a 5 loop system.

    Thanks again

  • ZmanZman Posts: 5,531Member
    Here is what I would do. Stop everything, go to the bookstore on this site, buy "hydronic radiant heating for the non engineer installer" and " pumping away".
    After you read and understand the books (and have a few laughs) come back and say "thanks so much Dan, now I get it, your the best".
    Then we can talk about the little stuff.
    If you are going to install these systems professionally, you want to truely understand them. Those books and a few pointers on here will get you there.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • onedrivenonedriven Posts: 7Member
    Hi zman

    Thanks for the comments, but I actually have that book by Dan Holahan hydronic radiant heating for the non engineer. I read it a while back. As as much as I would like to stop everything and read a few books I kinda need to learn this as quickly as possible. Like I said before I am an hvac contractor but mainly involved in furnace and a/c installation, I have some idea how the radiant system works but trying something that you are unfamiliar with is always difficult.
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