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Would like some feedback on my radiant design "plans"

Hello All,

I'm a long-time lurker, first-time poster.

I'm planning an underfloor radiant heat install in an ~1700 square foot well-insulated remodel. Total heat loss is ~18,000 BTUs at 0 deg F outdoor temp (I'm capable of and very confident of the calculation). Calc is room-by-room. Floors are either 1x6 pine topped with fir strip floors (and maybe 40% coverage with area rugs - average R-value with rugs of ~2.9) or 1x6 pine topped with 1/2" subfloor topped with linoleum (the real stuff, average R-value 1.9). I've used a variety of charts and tools from Healthyheating.org to calculate heat dissipation from fir strip floors as 12 BTU/hr and for the linoleum floors of 16-17.5 BTU/hr (depending on location and exact construction) with 110 degree water and 9" PEX spacing with good quality (thick) plates.

The heating system is a GSHP wtih a large water storage tank. I have an 8 manifold system set up. There is a Grundfos Alpha II pump to push water through the zones.

I've done complete calculations to understand how much heating I'll get at different water temperatures (I'm completely capable of this). Other calculations show an ~0.5 to 1 gpm flow with 0.5" inner diameter PEX (need 0.5" to keep head loss down). My longest runs are 400' total 0.5" PEX (head loss ~15 feet). Downstairs, I'm planning on one zone with a master thermostat (the floor plan is very open) and upstairs (three bedrooms and a bathroom) individual zones with a thermostat in each room. Two of the larger downstairs rooms with larger, older windows will be augmented with cast iron radiators (this is necessary to supply the required heat at cold temperatures). I can get the heat I need with 120 deg F water temperature at 0 deg F outdoor temperature (low water T with outdoor reset at higher outdoor Ts).

Here are my basic questions I'd like to get answered and then I'm happy to listen to any other suggestions/ideas as well:

1. If I reduce the PEX spacing to 6" from 9" (or 8") (effectively putting three 4" plates in one joist bay instead of two 4" plates), I don't seem to get much more radiated heat off the floor (I see maybe a factor of 1.125 more heat). Is that the case?

2. The pump I have already installed is a Grundfos Alpha II. If the head requirement at 1 gpm is for the longest loop only, then that has what it takes, from what I understand. But if all loops are calling for heat, will it just divide it's total ~4.25 gpm pumping capacity (at 15 feet head) by all the loops (assuming equivalent frictional resistance) or will it fall short for some reason? At 0.5 gpm, head loss of 400' of 1/2" PEX is a lot lower...which sounds like it works in my favor as well...

3. I calculate a delta T of ~9 degrees F at 0 degree outdoor T (0.5 gpm per loop) and 5 degrees when at 1 gpm (fewer loops calling for heat). Everything I read says that is reasonable. Can anyone confirm?

4. What would be recommended for balancing flow on the first floor loops, seeing that they are all on one T-stat controlled zone? I am designing for (mostly) balanced temps, but I want to plan for some miscalculations or adjustment after we've lived in the house for a bit.

5. There is 100 year old felt paper between the 1x6 pine subfloor and the fir wood strip floor. Given that my water T will be 120 deg F (130 deg F worst case at -30 deg F outdoor T), everything I've read says that this shouldn't be an issue. Any comments?

Thanks in advance. I've learned a lot already from reading the posts and plan on learning even more now.


Comments

  • HenryHenry Member Posts: 758
    As a rule, we don't connect or install DYI or internet designs. We have architects and engineers asking us to connect radiant systems. NO! We use plans that are designed by the radiant manufacturer. There is no if I do that etc.. And it works every time. You are not saving any money trying to DYI but only risking a system that does not work well!
  • kenjohnsonkenjohnson Member Posts: 5
    I have not been successful getting my basic inquiries from radiant manufacturers answered, despite sending them detailed floor plans and room-by-room heat losses (which is what they request). Perhaps you could suggest some radiant manufacturers I should be contacting?

    There is nothing more I would rather do than just buy a design from a competent and capable supplier.
  • BrewbeerBrewbeer Member Posts: 348
    A couple of thoughts.
    Can you install on top of the sub floor instead of under?
    Can the loop lengths be reduced? 15 ft of head is a lot. Try to keep loop lengths the same.
    Look for other sources of information for dissipation assumptions to confirm what you are getting from your healthyheating sources . If you are good with a spreadsheet and understand the concepts, you can do the design yourself if you are using the right tools.
    Or you can buy the design software ...
    Hydronics crazed homeowner with self-designed high efficiency 3 zone low temperature baseboard system and professionally installed mod-con boiler w/ indirect DHW.
    My system design thread: http://forum.heatinghelp.com/discussion/154385
    System Photo: https://us.v-cdn.net/5021738/uploads/FileUpload/79/451e1f19a1e5b345e0951fbe1ff6ca.jpg
  • ZmanZman Member Posts: 3,564
    It sounds like an interesting setup. I don't see a need for a 3rd row in each bay.
    What are the lengths of all the loops? Post the loop lengths and I will run the flow rates for you.
    Your delta t numbers look about right.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • kenjohnsonkenjohnson Member Posts: 5
    Thanks for the comments and thoughts. I'm laying out the floor plate location on a floor plan in Visio and I'll post it with the floor plans, likely over the Thanksgiving holiday.

    The install is a renovation to an older home, so I have to install underneath already finished strip flooring.

    My assumption of 12-16 BTU per square foot from the finished floor seems pretty consistent with "rule of thumbs" I've seen elsewhere. The healthyheating.org site provided a nice chart so that I could derive it myself for the specific floor.

    I understand the need to keep loop lengths nearly the same. If I skip the 3rd plate, that should bring the largest loop length down by 125 feet or so. It would be nice to skip the third plate.

    15 feet head was calculated at 1 gpm - would be a lot less at 0.5 gpm (4 feet or so). Would get even less with 2 plates per bay (125 feet less loop length).
  • RichRich Member Posts: 2,262
    Ken ,

    I applaud your endeavour but have a couple questions .

    1. Is your heat load calc a room by room calculation ?

    2. Why would you limit or design your new system around a circ that you have on hand whether it is the right or wrong circ ?

    3. Zone it properly , regardless of how many zones it is now , make it right this time around . This is a complete reno correct ?

    4. Where are you located , city , state , climate zone ?

    5. Dis regard anything negative or questioning of HealthyHeating as some apparently have no idea whose site that is and that most manufacturer info actually comes from there or had input from there .

    6. The fact that you found healthyheating tells me that you have a real desire to do it right , are there issues that make doing it right difficult or prevent you from doing so ?




    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC 732-751-1560
    Serving most of New Jersey , Eastern Pa .
    Consultation , Design & Installation
    Rich McGrath 732-581-3833
  • keyotekeyote Member Posts: 590
    Consider radiant ceilings using the routed foam with graphite plates. you can do higher swt w/o fear of wood floors and no worry about floors being covered.
    400' really long loop Yeah i know what they say its BS keep them under 300 250 better still. this ll also reduce head, ease pump tighten dt. guessing bed loops will be closer to 250 ea so if all on one manifold balance easier too, just split into two zones
    your spacing down to 6" is probably reducing your tubing to 3/8 the min rad of 1/2'' is 8" the foam board btw is 8" loops and 1'' thick.

    BTW Im not a pro just someone who did this and in the biz airside
  • leonzleonz Member Posts: 100
    Installing hot water radiators sized for the heating load would be faster to install if you use PEX and the installation would be cleaner. They make beautiful radiator covers for them.

  • kenjohnsonkenjohnson Member Posts: 5
    1. Is your heat load calc a room by room calculation ? Yes, I've done a very complete and thorough calc for each room.

    3. Why would you limit or design your new system around a circ that you have on hand whether it is the right or wrong circ ? The circulator pump installed (Grundfos Alpha II) was originally installed as I was planning on cast iron radiators with TRVs, so would have been a great option for that. I can change this out, if needed, no problem, if there is something more suitable for constant circulation (design goal).

    3. Zone it properly , regardless of how many zones it is now , make it right this time around . This is a complete reno correct ? Yes, complete renovation, access to all walls and ceilings. Plan is one zone on the first floor (very open plan) and one zone per room upstairs (three bedrooms and one bathroom). Will have to have a good Q&A on the right thermostats for downstairs and upstairs zones.

    4. Where are you located , city , state , climate zone ? Location is in Central NY, about 50 miles southeast of Syracuse. Climate zone 4.

    5. Dis regard anything negative or questioning of HealthyHeating as some apparently have no idea whose site that is and that most manufacturer info actually comes from there or had input from there . It's hard to argue with an ASHRAE document on the HealthyHeating site...

    6. The fact that you found healthyheating tells me that you have a real desire to do it right , are there issues that make doing it right difficult or prevent you from doing so ? Going slow and doing it right. No money or schedule issues. I believe in doing it once and doing it right.
  • kenjohnsonkenjohnson Member Posts: 5
    Consider radiant ceilings using the routed foam with graphite plates. you can do higher swt w/o fear of wood floors and no worry about floors being covered. I won't rule out radiant ceilings, but my heat loss will only be 18 kBTUs at 0 deg F (~11 BTUs per square foot). My supply temperatures will be pretty low (115 degrees F for this load, as calculated today) even accounting for the R-value of wood floors with 40% throw rug coverage. My heating system is GSHP with outdoor reset and I'll be setting the ODR curve to optimize temps to be as low as possible with constant circulation.
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