(206) 949-5683, Top Rated Plumber, Seattle
Page 1 of 2 12 LastLast
Results 1 to 15 of 23

Thread: Radiant heat floor puzzle.

  1. #1

    Default Radiant heat floor puzzle.

    Hi folks,

    Short story: my new radiant heat installation doesn't work well. I'm having pressure related problems and seem to have no end of air in the system despite it holding pressure with no leaks.

    Long story: I have a very simple (at the moment) radiant floor heating system consisting of 10 zones on a 12 zone manifold. I'm using a Grundfos UPS 32-80/2 VersaFlo Cast Iron Circulator Pump 115V, 1/2 HP. I'm filling the system with propylene glycol using a 1/2HP utility pump. It circulates thru a 200K BTU on demand water heater.

    The manifold is: http://www.pexuniverse.com/12-branch...-heat-manifold.

    House is small. 700 sqft. basement, 700 sqft. main level, 500 sqft. bedrooms upstairs. Zones are: basement closet, basement bedroom, basement bath, living room, kitchen, pantry, foyer/bath, bedroom upstairs #1, bedroom upstairs #2, bath upstairs.

    I'm supplying and returning from the manifold with 3/4" pex. Individual zones are 1/2" pex.

    I managed to get it to work for a few days, and for those days, it worked wonderfully. Took about 12 hours to get the cement slab warm, then it was great. Then I noticed my cheap chinese pump was leaking. Hence the nicer Grundfos multi speed model.

    Here's what is happening: I turn the system on, and I'm only focusing on the basement 3 zones at the moment. Thermostat turns pump on, fluid flows and I get 1.2 GPM each thru the 3 zones. (Bedroom, closet, bathroom). Each is about 150-200' of 1/2" pex in concrete. Slowly, the flow rate slows to 1GPM, then .8 then .6 and finally flow stops and the water heater shuts off.

    I started off with a 1/8HP taco pump and upgraded to the $700 pump thinking that more power was needed. I get the same results using the utility pump and putting fluid into the system. After I shut it off, I have air in the system. I flush the air out, and restart the procedure. It works for a short time, then pressure falls and then it stops flowing.

    I've tried narrowing it down to 1 zone. Same result. I've switched to an upstairs zone. Same result. I've concluded I have some sort of vacuum leak or the pump is cavitating, or something mysterious is going on involving differential pressure and hydraulics.

    I get the same result when filling the system from a 5 gallon bucket of coolant, or when cycling the system when it's a closed loop.

    I have a pressure expansion tank installed. The system holds pressure of 30PSI indefinately, but I have no way of telling if there is a vacuum leak.

    Every time I cycle the system, I get air in the lines. They are white pex, so I can see the bubbles move (the coolant is blue).

    It's become something of a mystery. It's repeatable, consistent and baffling. There must be something stupid I'm doing or something I've missed. I'm sure someone here has run across this before and maybe has the answer.

    My next step failing any better advice, is to replace the manifolds with something I build myself with copper tubing and valves for each zone. I would loose the flow gauges, but I could live with that. I can install automatic valves and individual pumps for each zone if needed, but it seems like an unneeded step if my current manifold works with individual zone thermostats.

    Any ideas? Vacuum leak? Too much pump for the job? Cheap Chinese manifold? Forgot to install widget x in location y?

    Thanks,
    Dan

  2. #2
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Location
    Cave Creek, Arizona
    Posts
    25,624

    Default

    AIr does NOT leak INTO a system. It has to be either sucked in or pumped in, so you have to find the source of the leak, usually a pump shaft seal, but not likely with the pump you are using. You might be getting cavitation, which will separate entrained air out of the water, if the pump is "sucking" less water than it needs, thus creating a "vacuum".
    Last edited by hj; 01-23-2014 at 05:50 AM.
    Licensed residential and commercial plumber

  3. #3

    Default

    you have not mentioned presence of an air eliminator in the main loop? you should have an air eliminator and you want to make sure your pressure tank connection is closer to the inlet side of circulator.... note: air eliminators work better on the hot (feed) loop ... I would generally install a spirovent about 12" "before" (upstream) the circulator inlet....and the pressure tank connects into the bottom of the spiro via FPT connection in spiro

  4. #4

    Default

    Quote Originally Posted by mikeplummer View Post
    you have not mentioned presence of an air eliminator in the main loop? you should have an air eliminator and you want to make sure your pressure tank connection is closer to the inlet side of circulator.... note: air eliminators work better on the hot (feed) loop ... I would generally install a spirovent about 12" "before" (upstream) the circulator inlet....and the pressure tank connects into the bottom of the spiro via FPT connection in spiro
    The manifold kit came with an air eliminator installed on the return manifold. I initially used it as per the instructions, but it seemed to add more air than it eliminated, so I closed off the valve stem cap and forgot about it. Could it be faulty and causing all my problems? I assumed with it capped off that it was no longer in the system.

    Thanks!
    Last edited by dberryco; 01-23-2014 at 07:43 AM.

  5. #5

    Default

    Quote Originally Posted by hj View Post
    AIr does NOT leak INTO a system. It has to be either sucked in or pumped in, so you have to find the source of the leak, usually a pump shaft seal, but not likely with the pump you are using. You might be getting cavitation, which will separate entrained air out of the water, if the pump is "sucking" less water than it needs, thus creating a "vacuum".
    This is helping. Air IS getting sucked in. I'm 99% sure of that. And the 2 replies have given me an idea it's the air eliminator or it's connection to the manifold. I'll be checking it today to confirm.

    Thanks!

  6. #6
    DIY Senior Member Reach4's Avatar
    Join Date
    Sep 2013
    Location
    IL
    Posts
    1,251

    Default

    I think it would be interesting to have a pressure gauge on the input to the pump. It seems to me that the intake would have to go below zero PSIG to suck any air in.

  7. #7

    Default

    Quote Originally Posted by Reach4 View Post
    I think it would be interesting to have a pressure gauge on the input to the pump. It seems to me that the intake would have to go below zero PSIG to suck any air in.
    you are correct in your assumption... this happens when the pressure tank is connected to the system at a poor location....this is why it is important to have the pressure tank connect to the system close to the pump inlet....

  8. #8
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Location
    Cave Creek, Arizona
    Posts
    25,624

    Default

    quote; but it seemed to add more air than it eliminated,

    That could ONLY happen if there were a partial vacuum at the air eliminator, which, by definition, would mean that the pump was "sucking water" rather than pushing it. It could NEVER happen if your entire system were at design pressure.

    quote; .this is why it is important to have the pressure tank connect to the system close to the pump inlet....

    The pressure tank is supposed to be installed at the point of zero pressure change, which is at the boiler itself.
    Licensed residential and commercial plumber

  9. #9

    Default

    the point of zero pressure change IS the pressure tank connection

    if you had a heat source with a low flow resistance you could locate the pressure tank near the inlet (HJ's implication perhaps?)
    since you are using an on demand water heater you will have considerable flow resistance through the heat source so you will want the pressure tank connected closer to the pump inlet
    Last edited by mikeplummer; 01-24-2014 at 06:44 AM.

  10. #10
    In the Trades Tom Sawyer's Avatar
    Join Date
    Nov 2010
    Location
    Maine
    Posts
    2,938

    Default

    post a picture of the boiler, circulator, valves and manifolds
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  11. #11

    Default

    I ordered a new spirovent and will be here friday. I found that my old one was leaking. I'll post a follow-up in a few days either way. I'm pressing on with wiring at the moment since I've already passed my rough plumbing inspection.

    I was fortunate that my no-name (looks like a riefeng) uses standard 1" NPT pipe threads on the input/output of the manifold even if the pex connectors are some odd European standard.

    Relocating the expansion tank is probably half the puzzle, and of course the leaks on the suction side too.

    Thanks all for the help so far.

  12. #12
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Location
    Cave Creek, Arizona
    Posts
    25,624

    Default

    Air eliminators do NOT work good on the return line, because by then the air has already collected in the heating loops. And an air vent on the return side of the pump CAN suck air if the pump is creating a vacuum.
    Licensed residential and commercial plumber

  13. #13

    Default

    Quote Originally Posted by hj View Post
    Air eliminators do NOT work good on the return line, because by then the air has already collected in the heating loops. And an air vent on the return side of the pump CAN suck air if the pump is creating a vacuum.
    I hear my original post echoing regarding placement of spiro....replacing the old one with a new one in the same location on the return line wont help

  14. #14
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Location
    Cave Creek, Arizona
    Posts
    25,624

    Default

    quote; the point of zero pressure change IS the pressure tank connection

    The tank connection does NOT "define" the point. If that were true you could put the tank ANY WHERE in the system and it would work the same, but that is NOT true. The BOILER is the point of zero pressure change and ideally the tank should be connected on the boiler.
    Licensed residential and commercial plumber

  15. #15

    Default

    the pressure at the tank connection will remain and that is why it is the point of no change - the pressure at the boiler will vary with system demand. I don't know how to post pics or I would show you my source

Similar Threads

  1. Radiant floor heat question.
    By ingeborgdot in forum Electrical Forum discussion & Blog
    Replies: 13
    Last Post: 03-24-2010, 09:58 AM
  2. Radiant floor heat design help
    By Stilly in forum HVAC Heating & Cooling
    Replies: 10
    Last Post: 06-10-2008, 02:23 PM
  3. Hydronic radiant floor heat
    By crater in forum HVAC Heating & Cooling
    Replies: 35
    Last Post: 03-03-2008, 12:18 PM
  4. radiant floor heat??? Yes No Maybe So???
    By nocry in forum Remodel Forum & Blog
    Replies: 38
    Last Post: 02-19-2007, 01:26 PM
  5. Radiant floor heat pex questions
    By Randyj in forum Boiler Forum
    Replies: 21
    Last Post: 12-17-2006, 11:23 AM

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •