Help with hydronic radiant heat

Discussion in 'HVAC Heating & Cooling' started by alfpark, Jan 3, 2010.

  1. alfpark

    alfpark New Member

    Messages:
    10
    Location:
    Annapolis, MD
    I have a hydronic system. I currently have the boiler set @ 160-140 and have my mixing valve going to my radiant manifolds set to 150. I have a delta t of 20, I have 150F heading out of my loops and 130F returning. My floors are warm but I cant maintain house warmth. My stats had been set @ 68 which was comfortable during day and nights of outdoor temps in the 30's and 40's. Now temps in the teens and I cant hold room temps. Some rooms down to 60F and below. Still same out and return temps. Construction is new all rooms are insulated well. System is staple up under 3/4 advantech subfloor and 3/4 engineered hardwood. It has Foil double bubble with an air gap below and R13 below that. Any help or ideas will be greatly appriciated!!
  2. Doherty Plumbing

    Doherty Plumbing Journeyman & Gas Fitter

    Messages:
    810
    Location:
    Penticton, BC
    So you're sending water out at 160 and it's coming back at 140 but yet you're not heating up the room?
  3. johnjh2o1

    johnjh2o1 Plumbing Contractor for 49 years

    Messages:
    1,143
    Location:
    South*East
    Sounds like you need more loops. Who figured the heat loss? The problem will become worse as the temperature drops.

    John
  4. zl700

    zl700 DIY Senior Member

    Messages:
    237
    Location:
    Texas
    Theres alot more to Radiant design but, I'm curious

    What size tubing, whats its spacing and did you use any plates?
  5. alfpark

    alfpark New Member

    Messages:
    10
    Location:
    Annapolis, MD
    I am using 1/2 inch tubing. no emision plates but foil double bubble stapled below runs in each bay. R13 under that. Fred Seton design 8 in. spacing. outside temps are averaging 30 day teens @ night. cant hold inside any better than 60-65. Just pruged system loops for air. Some but not signifcant.
  6. alfpark

    alfpark New Member

    Messages:
    10
    Location:
    Annapolis, MD
    The temp has already dropped!! I have 2 runs per joist bay 8 inches appart dont even think I could fit more.
  7. Doherty Plumbing

    Doherty Plumbing Journeyman & Gas Fitter

    Messages:
    810
    Location:
    Penticton, BC
    Are you sure the thermostat is accurate and functioning properly??
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,950
    Location:
    New England
    It doesn't take much air to block flow...you might want to purge the lines again...
  9. zl700

    zl700 DIY Senior Member

    Messages:
    237
    Location:
    Texas
    What are the surface temps of the floor during operation?
    Also, please share square footage of home, number of loops, loop lengths and I'll run some basic calcs.
    Any rooms without radiant or have other sources of heat?
    Last edited: Jan 5, 2010
  10. alfpark

    alfpark New Member

    Messages:
    10
    Location:
    Annapolis, MD
    My house is 2 story approx 1300SQ' per floor. 8' ceiling on second floor 9.5 on the first. There is currently 8 1/2" loops (4 on each Floor) 8" on center. I have a taco 0011 pump achieveing a flow of about .6 GPM with all loops open. My output temp is 150 return is 130. getting air out made a slight differnce. Still only able to get 65F durring the day downstairs. Upstairs with doors closed I can get 67-68 durring the day. Zones seem to be all calling @ night and I hold low 60's downstairs mid 60's up but constantly circulationg.
  11. alfpark

    alfpark New Member

    Messages:
    10
    Location:
    Annapolis, MD

    My floors feel warm not sure what to use to get a floor temp? Regular thermometer?
  12. zl700

    zl700 DIY Senior Member

    Messages:
    237
    Location:
    Texas
    Infrared is best but just find a thermometer and lay on floor and cover with a towel wait, and take reading
  13. zl700

    zl700 DIY Senior Member

    Messages:
    237
    Location:
    Texas
    Infrared is best but just find a thermometer and lay on floor and cover with a towel wait, and take reading.

    I don't know where you live so I am guessing your heat loss is in the 80,000 to 95,000 btu range.

    So your loop lengths are around 210-230' each?
    With a total of about 2000' stapled under the floor right?
    Although 150 degree water for the floor is excessive and way higher than most designs are done, I know why you need it. ( I would rarely exceed 120-130 under hardwoods at 0 degrees outside).

    At best you are transmitting 55,000 BTU to the home for heating.

    Without a detailed heat loss and design, you seem to be shy about 30% of emitter needed. This can be done with supplemental heat such as an air handler, baseboard, radiant panels or fan convection units.

    The best thing to do and should have been figured up front was the use of aluminum transfer plates to attach the tubing to the floor which improves heat transfer and spread and would of allowed lower water temps,, contributing to higher operating efficiency. Perhaps too late for second floor but 1st floor may still be accessible. If you go that route, I recommend at least 60% of the tubing under floor to be plated. You may also need a second mix valve to dial in the 1st floor better once plates are installed.

    Radiant design and layout is a science, not sure who did yours but maybe you can go back after them.

    What are you using for air elimination?
  14. alfpark

    alfpark New Member

    Messages:
    10
    Location:
    Annapolis, MD
    Thanks for help

    zl700 thanks for all your help I have regular air scoops on 90 elbows(not sure of the proper term). My loops are actually 400+' each. Hence the larger circ pump. I agree the 150 is high I just bumped up to try to get warm. My design was done by Fred Seton.
    www.radiantdesigninstitute.com
    All material is from Blue Ridge Radiant they and Fred both said with proper foil double bubble wrap underneath in the joist bays that the transfer plates were not needed. www.radiantdesigninstitute.com/page4.html
    I can still put them on the first floor which is worse off then the second. The first floor is existing constuction had 1X8 lapboard exterior so even though brand new insulation not quite as tight as second floor. The first floor is also 9.5' ceilings over unfinished basement which has 1 loop per joist bay 8" center and has foil double bubble and R13 underneath. It has the boiler and a pellet stove in the basement and stays about 50-60 degrees.
    My dad has one of those infared thermometers. I will get temps for you today.
    I had some air and purged all loops a couple of days ago. Its is definately better but still cant hold 68-70 overnight on the firstor second. Second drops to 64-65 and first to 60 or below. What should I be able to get as a high temp and hold. 67 is comfortable when outside temp is 40ish and no windchill. If I get to where I hold high 60's I should be ok (but would love to get into the 70's even though I am sure I would never set it that high!).
    A couple serious questions I guess are the nail up fins that much difference? Its seems people used to strap copper up and have good outcomes with alot poorer insulation and window drafts!! I cant understand that a flat piece of aluminum can make 5-10 degrees difference especially in the secong floor where it is incased in an insulated bay and has no place to go. Also if I did a sandwich using quicktrax or something similar I would have the same amount of tubbing loops(BTU outut) as I do in the just bays 8" appart for the most part.
    The other question is my flow rate. If I dont have a good flow rate that effects me obviously. My delta T is about 15-20 depending on outside temp and how many loops are flowing (never over 20 but can hold 20) which obviously hinges on outside temp. I am maintaining a miniumum of .5GPM usually more(depends on # of loops open). My loop flows are always pretty equal GPM reguardless of # of loops flowing. Do I need more flow? I am not sure what this will change. I can put a larger pump in currently a taco 0011. Again thanks for the support and help.
  15. alfpark

    alfpark New Member

    Messages:
    10
    Location:
    Annapolis, MD
    Just checked my floor temps with an infared thermometer. Upstairs I got 77-80 moving around. (thermostat @ satisfied @ 70 all loops closed.) Today I was able to hit and hold 70-73 up there. (it was warmer here and sunny high upper 30's). @ 5PM no loops up there were open and it was holding!!!

    First floor I got floor temps of 70-75. Definately not as tight as upstairs. Drafts around entry doors and exterior walls. I hope the air bibbles were my prob we shall see its supposed to snow tonight and highs fri & sat in the low 30's sunday in the 20's. I am keeping my fingers crossed.
    I would still like some one to look over my drawings I will email them. Also would like to know what my GPM flow should be.

    I dont know much about it but could these outdoor thermostats help? Could the temp be dropping so fast after sundown that the loop can't keep up when it kicks on once indoor stat calls?
  16. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,950
    Location:
    New England
    An outdoor reset won't do anything for you if you need to run the loops that high. It basically can be set to adjust the loop temperature based on the return water temp and the outside. If cold outside results in a much lower return temp, it can raise the input temp. You are already running near the max for your system. On a mild day it might save you a little by lowering the input, but won't improve cold performance (at least as I understand it) since you shouldn't get it higher.
  17. zl700

    zl700 DIY Senior Member

    Messages:
    237
    Location:
    Texas

    You say 1 loop per bay, 8" on center, so you mean it goes down and back with 2 tubes in 1-16" bay?

    That .5 GPM, is that per tube?
    The tubing is attatched to floor or clipped into suspension hangers?

    Is that one Taco 11 circ for both floors? Is there a boiler pump? and not that it matters much what is your boiler?

    If you have autovents on top of tees, that is not only a lousy way to vent air, with the HV circ you have, depending on where their placed, they can actually introduce air. You should be looking at installing a Spirovent or similar.

    Some observations:

    1/2" shouldn't be run over 300', I prefer 250' (the shorter allows lower amp pumps, even floor temps and quicker reaction time)
    There are many factors involved but the usual design of 1/2 PEX for radiant is around 3/4 GPM per loop.
    Because of the loop lengths, that pump may be required and in fact may not be enough, which is poor design and commonly made as a mistake, I pay attention to all energy costs and with proper design a lower energy use circ(s) could have been applied.
    150 degree water with only 70-75 degree floors tells me the heat is not transmitting.
    With a delta T of 20 (normal design) it appears flow is proper, if it was overpumped is would be less and under it would be more, which still points back to amount of tube and or transfer of heat.

    Several pictures of boiler, piping and manifolds will tell the whole story
  18. alfpark

    alfpark New Member

    Messages:
    10
    Location:
    Annapolis, MD
    I will post some pics tomorrow.
    yes .5 per loop
    pipe goes down and back same bay 16" bays pipes are 8" appart.
    And yes I have autovents on 90's
    my boiler is 148k btu well mclain
    tubing is stapled to subfloor
  19. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    The simple answer here is that you don't have enough tubing in the floor to heat the house. There may be some design issues also, like 400' loops and possibly some pipe size issues but I will bet that you just plain are not getting enough heat into the house. A couple of toe space heater or even some fin tube baseboard will fill in the difference.
  20. alfpark

    alfpark New Member

    Messages:
    10
    Location:
    Annapolis, MD
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