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Radiant heat under subfloor

New here , I am currently in the process of installing a under subfloor radiant heat system in my home . Using 1/2 uponor oxygen barrier pex/ uponor extruded transfer plates. My only concern is I have a double 3/4 subfloor which to my knowledge is about an R2. About 1.5 inches thick of plywood . Im installing 1/8 schloter mat on top , then Porcelain tile . Running about 1250 ft of pex / 200 heat transfer plates (4ft) not cheap . (12ft ceilings is the area being heated and 800 sqft. )I will be spray roaming around the rim board in each bay . And using r19 to insulate under the aluminum plates and tubing then sheet rocking (it’s a finished basement underneath ) 
my questions are 
what temp will I have to run for the floor to be effective as the only heat source or is the subfloor to thick to begin with ? Have had much trouble getting answers in this matter .
The feed of the lines doesn’t allow me to put extruded Plates which run through the 16 oc joist / tgis 10” . The tubing of course runs parrell with the joists and the heat transfer plates are 10”oc 
So could I put hanging ultra fin plats on the feed  to prevent kinking the lines up against sub floor I will attach some photos for reference . Thank you all for your help in advance this is my first time doing this and I have tried to do all diligence. 

Comments

  • pjohn1993
    pjohn1993 Member Posts: 5

  • hot_rod
    hot_rod Member Posts: 18,279
    if it would be good to know the heat load for the various rooms. Then from that number you determine the required supply temperatures to supply that amount of btus. The goal is to not exceed 80-82 floor surface temperature for comfortable floors

    In some  instances with high load areas or thick floor assemblies you need some supplemental heat in the spac

    The system you installed gives you some of the best output. If it falls short running 125 -135 supply you either need to lower the load or add some additional heat. 

    So either try and see, how it works or do room by room load calcs to predict the outcome

    Be sure the tube moves freely in the holes in joists

    The Ultra Fin may get a small amount of additional output, you need to leave an air space under them for convection. With transfer plates an inch of gap is enough so you can get a batt below 




    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    pjohn1993
  • pjohn1993
    pjohn1993 Member Posts: 5
    hot_rod said:
    if it would be good to know the heat load for the various rooms. Then from that number you determine the required supply temperatures to supply that amount of btus. The goal is to not exceed 80-82 floor surface temperature for comfortable floors

    In some  instances with high load areas or thick floor assemblies you need some supplemental heat in the spac

    The system you installed gives you some of the best output. If it falls short running 125 -135 supply you either need to lower the load or add some additional heat. 

    So either try and see, how it works or do room by room load calcs to predict the outcome

    Be sure the tube moves freely in the holes in joists

    The Ultra Fin may get a small amount of additional output, you need to leave an air space under them for convection. With transfer plates an inch of gap is enough so you can get a batt below 




    Thank you for the fast response hot rod I appreciate it more then you know 🤘🏽Have seen a lot of you insights on other post here as well . 

    I had radiantec do a calculation ( I know they are not to be trusted after some stories I’ve read in here ) and the whole area is basically one room with a small bedroom and bathroom . The required btus for the space was about 32,000 due to the high ceiling / majority of the space is cathedral ceiling approx 15 ft to the point A frame angled down to the straight 10ft side walls, so it was difficult for me to assess the exact btus, but I’m not sure about the heat loss calc. As for the holes in the joist I know to expect some expansion with the pex so I drilled 1 3/8 holes through the joist . So they have some room to move about. I tried my best to leave them a bit of slack so it was not very tight . I did not do any expansion loops which I have heard of in some installs because I did not think it was necessary for the 1inch expansion every 100ft or so is this a problem ? 
    I stayed 8 inches off the rim boards so I can spray foam , thinking maybe I should have given myself a bit more room . 
    Do you think it would be best to spray foam under the radiant heat if I block it off with a foam board insulation to create the cavity required ? And is the cavity still required if I decide to not go with the ultra fins or could I just butt r19 directly underneath the lines ? 
    Also curious if spray foaming the roof and walls above would help because I was planing on spray foaming the entire home . 
    I’m slightly worried about the ultra fins causing noise as  well if I decide to use them  ,have heard some stories ..  I would only put them where the feed is directly under a floor space I need heated such as the bathroom or so / entire job is almost half way finished . - thank you for your time and knowledge everyone, it’s greatly appreciated 
  • The more insulation, the better. Adding Ultra-Fin would just be a band aid.

    From what you've told us, depending on where you are, you will be comfortable down to a certain temperature and then cold. You've got a few things working against you which only heatloss calc's. will make clear.

    Here's a calculator to help you find that BTU's per square foot number.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hourTwo btu/ per sq ft for degree difference for a slab
  • hot_rod
    hot_rod Member Posts: 18,279
    Is 800 sq ft the total heated space? With 1250 feet of pex you should cover 1000' sq ft 12" on center, depending o0n loop end runs.
    A room with 800 square feet of radiant panel with high walls could be a high load. How much glass in that room?

    Have you checked spray foam $$ these days. I went with 1" spray foam then fiberglass batts to make a good R value affordable. The foam seals every crack and glues the framing together :)

    Try running the load again with the calc Alan attached just to see how that room comes out. Easy enough to do a single room.

    If you do need some extra heat, maybe a few panel rads. You may run some pex before you insulate.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    spitmon1
  • pjohn1993
    pjohn1993 Member Posts: 5
    hot_rod said:
    Is 800 sq ft the total heated space? With 1250 feet of pex you should cover 1000' sq ft 12" on center, depending o0n loop end runs. A room with 800 square feet of radiant panel with high walls could be a high load. How much glass in that room? Have you checked spray foam $$ these days. I went with 1" spray foam then fiberglass batts to make a good R value affordable. The foam seals every crack and glues the framing together :) Try running the load again with the calc Alan attached just to see how that room comes out. Easy enough to do a single room. If you do need some extra heat, maybe a few panel rads. You may run some pex before you insulate.
    Yes spray foam is going to be quite expensive/ I like your idea of doing one inch and finishing up with fiberglass over it I’ll definitely do that. 
    I’m doing about 8-10” oc with the pex so it was slightly over 1000 ft I should have a bit left over . Got a lot more of the work done yesterday morning I’ll be sure to send some photos . 
    Is it okay I dident use expansion loos for this set up in your opinion ? 
    There are a few very large windows but majority of them are  tempered glass and do not open / I’m leaning towards installing a large modern radiator above the stair case on the wall to supplement the heat and it’s a also going to add to the industrial farm house design I’m going for And it’s a bad **** design ! Here are some photos of the upstairs 
  • pjohn1993
    pjohn1993 Member Posts: 5
    The more insulation, the better. Adding Ultra-Fin would just be a band aid. From what you've told us, depending on where you are, you will be comfortable down to a certain temperature and then cold. You've got a few things working against you which only heatloss calc's. will make clear. Here's a calculator to help you find that BTU's per square foot number.
    Hey Alan thanks for the response ,  I’m on the Jersey shore , I’m having trouble accessing tht app on my iPhone do they offer and way to do it on a computer? Thanks 
  • hot_rod
    hot_rod Member Posts: 18,279
    As long as you don't put any tight clips or restraints on the pex, it will move side to side, grow a bit in length, no need for expansion 180 loops. Ideally run on outdoor reset so the tube never sees wide temperature swings, that is the best way to minimize expansion concerns.

    Glass to the right of the stairs also? Better do a load calc. on that space. Window coverings can make a big difference on large glass also., especially with a couch or chair right in front of cold glass.

    At the very least run a pex S&R to where a panel rad could be added, run it with a TRV that could bring it on if temperature drops.

    As for insulation, price blown in chopped cellulose over the 1" foam also. I see that done around here. Sometimes with chopped up blue jean material :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 3,517
    edited November 2022
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hourTwo btu/ per sq ft for degree difference for a slab
  • kenjohnson
    kenjohnson Member Posts: 80
    Hello fellow radiant installer, I designed and installed my own radiant floor system with 1/2" pex in Uponor extruded aluminum plates underneath 1" pine subfloor that is underneath 3/4" oak or fir strip floors. It works fine in my installation. I would caution that my heat loss for my entire house is about 18,500 BTUs/hour at 0 degree outdoor temperature, and I am running a couple of degrees of supply temperature below my calculation (i.e., my system is performing slightly better than expected). You can mostly forget about area rugs on the floors. Your results may be different - my heat loss on my ~1000 square foot first floor is about 11,000 BTUs at 0 degree outdoor temperature, and my radiant supply water temperature is 120 degrees F at that outdoor temperature.

    My post about my system is here https://forum.heatinghelp.com/discussion/163346/would-like-some-feedback-on-my-radiant-design-plans#latest

    Ping me if you have any questions. I am happy to answer any questions that I feel qualified to answer, and willing to say "I don't know". I did learn a lot from this forum and other resources and I did do the entire design of my system, from room-by-room heat loss calculations to pex layouts to supply system configuration.