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Best DIY way to remove Air or Sludge?

We are having a cold snap here in CA, and my radiant floors just don't keep up anymore. I posted last year about changing from Grundfos 15-58 pumps (one went bad with noisy bearings) to the Alpha pumps. The Alpha pumps heat the house OK when set on the highest setting (the auto adapt setting just doesn't work at all) and the outside temps are foggy and 55. The old 15-58 pumps worked so much better under identical conditions, and I don't know why. But it's 40 outside, and the floors are not keeping up.

It's an old Victorian with staple-up system, with alum. plates and good insulation. (And the larger failure here, I know, is that the 7/8" pex is 16" o.c. and should be 1/2" with 8" o.c.) STILL, it never seemed to matter much because SF temperatures are mild, and it works well enough most of the year. With the old pumps, getting the house to 72-74 when it is 55 outside is easy. Now with the alpha pumps on high, I can barely maintain 68 degrees, when it is 40 outside.

I am theorizing that there is air in the system, or sludge in the system, or frankly, the water just isn't moving. It's only 10 years old. I purged the air when I changed the pumps, by connecting a pump and hose and flushing out the system for over an hour, until way after the hose stopped bubbling in the transfer bucket and the water ran clear.

So for a licensed contractor like myself---who should know ;-) after all, what is the best way to assure that all the air or sludge (if any) has been moved out--I need some suggestions. I'm lost at this point.

Ideas? Suggestions? Links?

Or should I try larger pumps? I am not sure a larger boiler would make a difference, but what to you all think? I have a Triangle Tube solo 60 now. The heat loss on the house is only 42,000btu/hr. If I had the Triangle 80 boiler, that would not make much of a difference, no? To me, it's the pumps or the tubing having air that may be the issue.


  • SWEI
    SWEI Member Posts: 7,356
    A larger boiler will do nothing other than short cycle and wear itself out.

    How is the system piped and pumped? Do you have a diagram, or at least a photo of the piping and pumps near the boiler? Is outdoor reset being used? If so, what are the settings?
  • RobinInCali
    RobinInCali Member Posts: 30

    The old 15-58 pumps worked so much better under identical conditions, and I don't know why.

    I do.

    Take a look at the pump curves.

    Look at the single operating point of 16 feet. The 15-58 will flow 4 GPM. At the same 16 feet, the Alpha flows just a bit over 2.5 GPM.

    If the floor needs 4 GPM to deliver the BTU's required, you'll observe a fairly sizable ΔT with the Alpha.
    That was my first guess, too. I happened to have a spare 26-99 pump in my truck, so I exchanged the Zone 1 (joist) pump for that, to see if there was improvement. There is still no difference in the heating quality in the joist part of the house. Which means that with more pressure, and significantly more gpm, I'm still not getting heat out of the floors.


    Boiler supply water is coming into the system 3gpm, at 138 degrees (and yes, I have an outdoor reset, which increases the water from the normal 110-120 when it is above 60 outside; up to 140 when it drops below 52 outside.) Return water temp is 123 degrees, so that's a delta t of around 15. Good. But the house isn't getting past 68 air temp, with the system running 24/7.

    If this isn't a blockage, I can't think of another reason.

    I mean, all we are talking about here is that it's cold outside. I can't imagine how a drop of 5 degrees outside renders the system helpless to keep up.

    Boiler set up is a primary/secondary loop. Two radiant zones, with 1 1/4" manifold serving them, 3/4" outlets going to 7/8" pex. in staple up for Zone 1, and 7/8" in concrete slab for Zone 2. Then 3/4" return outlets to the 1 1/4" return manifold.

    15-42 Pump on the primary loop, closely spaces t's, and an alpha pump for each zone.

    Finally, when a 26-99 pump is substituted for one of the alpha pumps (on the zone with the joists, which is the problem) there is no increase in temperature.
  • RobinInCali
    RobinInCali Member Posts: 30
    Sorry, I will try to clarify. The boiler is heating and delivering 3gpm of 138 degree water to the floor--which it always has--and the pump is pumping 10-12 gpm out to the floor, mixing it with the cooler return water (closely spaced t's). The point is, 125-135 degree water is circulating in the system. This is used to keep the floors and house a toasty 70-72 degrees running 8-12 hours per day. Now it's hard to get past 68 running 24/7.

    I hope that clarifies it? Or does it make it worse? ;-)

    I'd thought that some air pockets were at work, or maybe some sludge (there are spots of cool flooring amongst the warm, which is not usual). That's why I'd asked about how to purge air and sludge in my post.

    Thanks for your help!
  • RobinInCali
    RobinInCali Member Posts: 30
    I am not ignoring it, but perhaps I can be clearer: I will answer your exact questions. Hope this helps.

    *I now understand that the boiler loop is flowing 3 GPM. I ask did you measure it?

    The digital monitor off the boiler states that water is entering it at 121 degrees, and exiting at 138, and is flowing at 3.1 gpm.

    *I also asked to know what is the ΔT in the system loop (the floor)?

    The analog temperature gauge on the output manifold pipe reads 138, and the input manifold pipe reads 121-125. That is the delta t.

    *I also asked for the design day outdoor temperature.

    The design outdoor temperature for this house (San Francisco) is 36f, with 42,500 btu being the heat loss.

    36f seldom happens, like maybe once every 10 years; we usually only get down to 44f to 48f during the Dec cold snaps). That means the system need only produce a 25-30f degree rise from outside to inside. And usually, the outside temps aren't much below 50f. This systems works fine if it's more than 50 outside.

    This past week, it got down to 40, and the interior of the house barely made it to 67-68 for several days, boiler working 24/7.

    *You have ignored all of the above.

    Hope now, you see I have addressed the issues.

    *I would also like to know how you measured the 10-12 GPM flow rate to the floor?

    I assumed that with the Grudges 26-99 pump going on the hi speed, it would be nearly that, according to the spec sheet.

    *If you continue to believe that you have a flow problem, nobody can help you.

    I no longer believe I have a flow problem because the 26-99 pump accomplished nothing. I now believe I have a "what the hell is it" problem.

    Cheers! Thanks!
  • RobinInCali
    RobinInCali Member Posts: 30
    Delta T is the difference between the incoming temp and the outgoing temp. It varies 12-16, so I averaged it out.
  • RobinInCali
    RobinInCali Member Posts: 30
    I recall seeing a ΔT of 5 degrees in the past. But not now. Also:

    In fidgeting with it, by turning up the boiler to 155 degrees, then on up to 168 on the boiler, I see the flow rate go down to 1.8 gpm and yet (!) the supply manifold thermometer staying nailed at 138.

    How... Wow. How can the water temp be 168, and the supply manifold one foot away stay at 138? I left it on for a half hour, and very little increase in the water temp at the supply manifold.

    Is it pulling too much from the return? From the closely spaced t's? Wouldn't it still heat up overall, with even the paltry 1.8 gpm/higher temp flow?

    So the problem is with the boiler, then, not producing an adequate flow rate? Or the piping?

    I see there is a larger problem now, obviously.
  • RobinInCali
    RobinInCali Member Posts: 30
    Also measured the gas use overnight. Per gas meter, boiler is burning 57,400 btu per hour. Yet less than half is getting into the floors.

    The main thing that led me to post here is the low temps, and yes, splotchy heat on the floors. Warm in places, cold in other places. That's why I assumed sludge/air in the beginning.

    Boiler output of 3gpm when at 140, 1.8 gpm when at 155, yet temps a foot away don't reflect a change.

    Boiler should output twice that gpm, no? And certainly the temp gauge should reflect the hotter water.

    I will post a diagram of pipe.
  • RobinInCali
    RobinInCali Member Posts: 30
    So, I cleaned out an in-line sediment filter, and removed the primary pump. Filthy inside. Cleaned it too. And now I am getting 3.4 to 3.5 gpm out of the boiler. I bet that's at least part of it.

    House temps back up. But surely I should get more than 3.5 gpm out of the boiler, when it's heating the water only 20 degrees?

    So again to the beginning. Filthy water, sludge. How to remove.

    Thanks for any further advice.

  • hot_rod
    hot_rod Member Posts: 15,028
    Closely spaced tees are the only mixing device?
    Any change in floor coverings or furniture? You can buy a hydronic cleaner kit from Fernox or Rhomar to desludge a system
    Is it non barrier tubing? That tube has a habit of slugging systems.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • jumper
    jumper Member Posts: 1,710
    If all pipes are non-collapsible fill under vacuum like refrigeration guys do it. Otherwise any hydronic system should have access to suction well above pump. Hot water heats better with less air. Just about nobody does that in non-institutional buildings and that is why people have problems.
  • RobinInCali
    RobinInCali Member Posts: 30
    Updating, all these months later... Through this forum, and extensive reading and study about radiant systems I discovered: The tubing was installed incorrectly. Not spaced closely enough, and the loops are wildly different lengths, so they're not balanced. Hard to solve that without tearing out the whole thing. And the house is warm enough 10 months out of 12.

    I am now relocating the boiler and panel for a remodel, unrelated to my radiant woes, and I will attempt to balance each loop so the heating is more even.

    I've drawn a conclusion over these years, which is that the flow naturally rushes to some parts of the loops, and lags greatly in other loops.

    I wish I could tear out all the ceilings where the staple up exists, and re-do the tubing. But that would cost north of $30,000, because the staple up is over a finished living space. The heating issue is not really that bad.

    I hope it improves with this boiler relocation.
  • pecmsg
    pecmsg Member Posts: 2,322
    What do you have for cooling? Perhaps a Hot Water coil to warm the air!
  • RobinInCali
    RobinInCali Member Posts: 30
    For cooling, I have the Fog coming in over the Bay every day. Nobody in coastal California has AC. Even inland in Napa, even in the Summer it gets in the 90s, but cools down at night. You gotta wear a jacket.

    There's maybe one week of heat wave each year. In SF you swim in the Bay. In Napa, you just drink more wine and turn on a fan.
  • RomanP
    RomanP Member Posts: 102
    edited May 2018
    I’d like to see photos of your system. Manifolds if any, primary secondary configuration.... everything. How many radiant loops do you have?

    I do hope you are pumping away, right?
  • SuperJ
    SuperJ Member Posts: 605
    Sounds like insufficient primary flow causing reverse flow across the closely spaced Tees. If a zone is flowing more than the primary loop, then the swt to the zone will be diluted down from mixing with the return.
    Also, Is the high temp staple up zone the first set of tees to get access to the hottest water?
    A single Alpha should easily be able to handle the flow for a 40kbtu heat load in a properly designed system. If you have one on each zone you have tons of pump.
    Autoadapt and the constant pressure modes are for adapting to zone valves. If the pump is dedicated to a single constant flow zone, one of the 3 fixed speeds should be suitable.
  • RobinInCali
    RobinInCali Member Posts: 30
    "insufficient primary flow causing reverse flow across the closely spaced Tees"

    I bet that's it. So I should have a larger pump on the Primary? I currently have a Grundfos 15-29 fixed speed.

    All pumps are stainless, because the tubing the former owner used was not oxygen barrier. He had an open system, but I replumbed it as a closed system. Everything is stainless, including all Alpha pumps and the boiler (tube).

  • RobinInCali
    RobinInCali Member Posts: 30
    And to answer the other guy's question, I have three loops for staple up Zone (off one Alpha Pump) and two loops for the slab zone (off the other Alpha pump).

    One mistake I've considered is (and I will correct this for the new panel I'm doing in the Boiler relocation) the slab zone does come first in the sequence.
  • SuperJ
    SuperJ Member Posts: 605
    edited May 2018

    And to answer the other guy's question, I have three loops for staple up Zone (off one Alpha Pump) and two loops for the slab zone (off the other Alpha pump).

    One mistake I've considered is (and I will correct this for the new panel I'm doing in the Boiler relocation) the slab zone does come first in the sequence.

    You definitely want to supply the staple up first since the cold return from the infloor is going to reduce your SWT. Increasing the SWT even 5degF will have a big effect.
    • Change the order so your high temp load comes first
    • Primary Flow boost - Avoiding reverse flow across the Tee's
    • Primary Flow boost - ensure you have enough flow bypass the Tee's so that the SWT to the next set of Tees is closer to the boiler SWT than the RWT from the first zone.
    One thing to consider is where the system sensor is. Your boiler may support a remote system sensor. Depending on where you place this, the boiler could raise it's SWT to compensate for mixing/dilution occuring at the Tee's or between sets of Tees. this allows you to have a lower primary flow since the boiler will discharge water above setpoint to compensate for the mixing and keep the temperature constant at the sensor.

    Of course getting your system clean is the first step. I would put a good dirt/mag separator on the return and some inhibitor to try and keep it clean going forward after you flush it.
  • SuperJ
    SuperJ Member Posts: 605
    edited May 2018
    Looks like that little primary pump isn't enough. 15-29.
    You should probably be using a 15-58.

    EDIT looks like the 15-29 is a bit less than the 15-58 on speed 2. It is an appropiate pump, but a 15-58 on speed three will give you a couple GPM extra.

    May consider repiping your primary like this since you already have a bunch of pumps.

    I've marked the 15-29 curve in red dots for comparison.

  • RobinInCali
    RobinInCali Member Posts: 30
    I have a good condition used 3 speed 15-42 pump on my shelf, a stainless one, which I'm going to put on tomorrow. I will report back with results.

    Y'all are awesome.

  • RobinInCali
    RobinInCali Member Posts: 30
    That's a great graph. It appears you mean I should place the boiler pump on the hot supply side, instead of the return side. Yes?
  • RobinInCali
    RobinInCali Member Posts: 30
    edited May 2018
    I also used Fernox to clean it out. I flushed it, then started using a Caleffi Hydro Sep with the Dirt Mag gizmo, and the results were quite good. I seldom have gunk anymore.