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Radiant Letdown

LMJ123 Member Posts: 6
Does anyone know of a radiant heat expert in Albuquerque, NM? I've had three plumbing companies come out who have claimed radiant expertise, but have been able to do little more than verify that the boiler works. So, I've resigned myself to learn as much as I can online. I've already verified that all of the equipment in my system works correctly, but am concerned that the issues I'm having are more likely design issues. I would love to find an expert and hear on this forum of possible solutions. If there's not someone locally available then hopefully I can get some answers from the experts here and proceed with the work myself.

2500 sq. foot single story home w/ in-floor radiant (all on a concrete slab) installed in 2005. I purchased the home about a year ago.

Weil McLain CGa Gold 140,000 BTU Non-condensing Boiler (at 6000' above sea level)

Honeywell Aquastat AQ475A w/ outdoor reset (Current configuration: minimum temp is 100, max is 120)

Taco 007 (plumbed in right before the return enters the boiler)

Honeywell T8400 2-wire thermostats (only air temperature, nothing on the floor)

11 total loops controlled by 8 thermostats with Wirsbo pop-up valves. Six thermostats each control one valve (loop), one thermostat controls two valves (loops), and one thermostat controls three valves (loops).

Supply from boiler is 1.25 inch that is teed into two .75 inch branches with each going into a manifold. One manifold has six loops on it (bedrooms) , the other five loops (living area). Each loop is .50 inch pex. that returns into manifolds with the Wirsbo pop-up valves. The boiler feeds its supply directly into any open zone. In other words, there's no boiler loop independent of a radiant loop that does any kind of mixing. The supply temperature coming out of the boiler is what goes into the floor, hence the setting on the Aquastat of 100 (minimum) and 120 (maximum), which doesn't sound great given that this is a non-condensing boiler. On the other hand, it only runs about three months a year given our climate. Perhaps that is why the installer went down this path? I've seen a couple of neighbors systems as well and there systems also don't have any mixing, although they say their systems work great.

Currently, the boiler will start to cycle in the evening and run through most of the night with all 11 zones getting heat as all 8 thermostats will eventually start calling for heat within an hour or two of one another. The boiler will stop early morning and stay off for roughly the next 12 hours and then repeat the same cycle coming on the following evening. Given this 12 hours on, 12 hours off cycle, the temperature generally overshoots throughout the morning (I imagine too high a supply temperature) and then falls 2-3 degrees behind the setpoint by late evening (the thermostats call for heat once below the setpoint, but don't see any response from my slab for hours). I started up the radiant last year about this time and ran it for a month, but was averaging 10-15 therms of gas consumption per day. I shut it off and just ran the forced air-furnace, which averaged 3-5 therms per day. This year, I would prefer to get the radiant working since we purchased this house for the radiant due to severe asthma problems.

What do I need to do? My thought based on the hours I've pored over the Internet.

1. Figure out how to create a boiler and radiant loop with mixing?

2. Buy a bigger pump? (I've tried to do the calculations, but have had to guess on loop lengths to calculate head loss and heat loss for gallons per minute. That being said it always seem like the Taco 007 ends up being on the small side for circulating the entire system)

3. Replace these cheap thermostats? (I've looked at the Wirsbo WT1 thermostats for radiant)

I would appreciate any advice. Am I on the right track? Am I missing something? Who in Albuquerque knows radiant?


<a href="https://plus.google.com/photos/109896760638991316254/albums/5950598358431233073?authkey=CPONwYeK_ZeiUg">https://plus.google.com/photos/109896760638991316254/albums/5950598358431233073?authkey=CPONwYeK_ZeiUg</a>


  • Gordy
    Gordy Member Posts: 9,546
    edited November 2013
    First thing

    Heat loss calculation room by room. Rule number one. Without it you have no idea what water temps, and flow rates you need to off set your heat loss, and verify your tubing layout is going to work.

    Your burning of 10-15 therms a day in a 12 hour period. at what outdoor temps, and what was the indoor set points of the thermostats? Was this an average therm usage off the gas bill? That ends up being 21 btus a sf using gross input average over a 24 hour period.

    You say you have a slab. Can you verify it was insulated both perimeter, and underneath?

    Can you verify the supply, and return temperatures from the boiler?

    Can you verify supply, and return temperatures of the radiant loops?

    Are you setting back the system? Radiant works best being left at one set point.

    11 loops for 2500 sf works out to 1' centers with average loop lengths of 227' which is fine. IF the heat loss calc allows it.

    No mixing valve on the boiler is a problem to the boiler it will condense, and have a short life 3 months a year or not. Neighbors not having one or not.

    Lastly some pictures of the boiler room showing piping, and manifolds, thermostat types.

    Being that boiler is at 6000 feet was a combustion test done? If over 2000' in the manual some changes need to be made to the combustion. Was this verified to be correct. If not your boiler is not going to put out it's rated output. 140000 btus is gross input. 117000 btus is doe capacity, and 102000 btus is net IBR. Is this a series 1 or 2 cga?

    I have a feeling your boilers combustion may not be set right seriously debating the boilers output. Causing high gas usage.

    Do you get a lot of solar gain during the day?

    Finally floor sensing thermostats will help. Along with outdoor reset if you do not have it.
  • LMJ123
    LMJ123 Member Posts: 6
    edited November 2013
    Radiant Letdown Pictures

    Here's a link to pictures. Thank you for your reply.


    I will work on answering the questions in your posts later today.
  • pixs

    Pixs are too close... back up so we can see the whole system!
  • LMJ123
    LMJ123 Member Posts: 6
    edited November 2013
    Pix too close

    The picture of the boiler is the entire system that is in the garage. The manifolds are located about 25 feet away in closets inside the house. To the left of the boiler, it may look like there is more to see, but that is just the hot water heater, which is completely independent of the radiant system. All that is in the garage is the boiler, aquastat, Taco 007, and a 1.25 inch supply that goes into the wall, and a 1.25 return that comes back out. There is no other piping until you look in one of the closets inside the house. One closet contains a five loop manifold with a .75 inch supply and return (pictured). The other closet contains a six loop manifoled with a .75 inch supply and return (not pictured). I can work on taking more pictures tonight, but I'm afraid there's not much more to see since there are no separate boiler and radiant loops, and everything is circulated off of the single Taco 007.
  • as far

    As far what I can see in these limited photos, a good brand boiler is piped wrong
  • SWEI
    SWEI Member Posts: 7,356
    Albuquerque radiant heating pro

    I sent you a PM with a contact at one of our wholesalers in ABQ who should be able to hook you up with a competent contractor.  We're four hours south of you or I'd offer to come take a look myself.
  • LMJ123
    LMJ123 Member Posts: 6
    Updated Pictures

    RJB: I've updated the pictures and added captions.

    SWEI: Thank you for the PM.

    Gordy: Thank you for your post, here's more info.

    I've been reading my gas meter every evening so I know what I've used over the previous 24 hours. The reading Saturday, Nov. 23 was 12.5 therms, Sunday, Nov. 24 was 12.5 therms, Monday, Nov. 25 was 13 therms. Thermostats are set at 66 and the weather on all three of those days had highs of around 35 and lows of about 27.

    I'm not sure how to verify slab insulation. I can dig around the perimeter and see if there's anything other than concrete below grade, but not certain how to verify anything underneath the slab. I don't have any information about who did the radiant installation when the house was built in 2005.

    The supply temperature on the boiler is set to 120 on the Aquastat and the temperature gauge on the supply kicks off as soon as the boiler hits 120. There's no temperature gauge on the return to the boiler, but even after it has run for hours my hand tells me it's probably around 80. I think the differential is usually 40 or more degrees. It can cycle for a couple of hours (about one hour of the boiler firing) before the return even begins to change temperature.

    There aren't any gauges on the supply or returns for the loops. I've felt both of them by hand and they are rarely ever more than warm to the touch. I've ordered an infrared thermometer to try and take more accurate measurements.

    As far as set back, I don't change the thermostats. One zone is off, two are always set at 65, and the remaining five are set at 66.

    I've updated all of the pictures. See the link added in my original post. The only thing missing is a picture of one of the two manifolds. Each of the two manifolds are in a closet inside the house. I took a picture of the one that is easiest to access, but the other is identical other than it has 6 loops on it instead of 5.

    I don't believe anyone has done a combustion test. They sniffed for gas leaks, and visibly viewed the boiler while running, and it creates a nice blue flame. I've included a picture of the tag on the boiler saying it has been modified to run at altitude. I also included a picture of the boiler information. It looks like it is a CGA-5-SPDN, you can zoom in on the picture to read all of the boiler info.

    We get very little solar gain. The house faces southeast, but that almost all garage other than one of the bedrooms.

    The controller has outdoor reset, but I don't think there's much it can do as far as reset with a boiler minimum of 100 and a maximum of 120.

    Thank you for your post. I do appreciate your help.
  • Gordy
    Gordy Member Posts: 9,546
    edited November 2013
    Weeding out variables

    So good boiler is set for altitude.

    Slab insulation questionable.

    Outdoor reset part of the system.


    No mix valve for radiant.

    Possible miss matched circ sizing.

    No air removal device. Possible air bound loops.

    Not piped primary/secondary.

    High fuel consumption.

    Over shoot on setpoint.

    Long burn times to reach set point.

    I would take SWEI up on his offer . Get a HYDRONIC pro in there to plumb mix valve in for boiler protection, and circ sizing along with fine tuning outdoor reset. Possible other piping issues such as boiler not plumbed primary/secondary.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    No mix valve for radiant.

    I do not have a mix valve for my radiant, but do not need one.

    My boiler has two reset curves. One is used when putting heat into the radiant zone. The other is used when putting heat into the baseboard zone.

    If both zones call for heat at once, the priority system supplies radiant zone reset curve and temperature to both zones. Putting radiant temperature water into the baseboard produces some heat, but not really enough.

    After 1/2 hour, if baseboard zone thermostat is not satisfied, it gets priority for 20 minutes. In that case, the circulator to the radiant zone shuts off, and the boiler supplies baseboard reset curve and temperature to the baseboard zone only. Then it reverts to normal priorities and temperatures for 30 minutes. Rinse and repeat.

    Since my baseboard zone takes very little heat, this is sufficient.
  • Gordy
    Gordy Member Posts: 9,546
    Cast iron boilers

    Jean you don't have a ci boiler that's why
  • Gordy
    Gordy Member Posts: 9,546
    To the original poster

    One more variable to weed out, and that is if rooms have high rvalue floor coverings? That would increase response time and cause set point over shoot.
  • LMJ123
    LMJ123 Member Posts: 6
    Hydronic Pro on the way...

    Thanks to SWEI, I was able to get in touch with his recommendation before Thanksgiving and they will be out in the coming week.

    Gordy: Thanks for all of your help. As far as the floor coverings about half of our square footage is ceramic tile, and the other half is polyester carpet that is pretty plush. 60oz face weight with a 5/8 thick rebond pad under it. The carpet was in the house when we purchased it, but plan to replace it with the rubber waffle board padding and a lower face weight or just go with engineered wood or laminate once I'm not longer pumping 120 to 130 degrees straight into the floor. I've been working on heat loss calculations and calculating head loss based on loop sizes of ~227ft based on your original post. I calculate a minimum of 10 ft of head, which based on the pump curve of a 007 means very little flow. My infrared thermometer arrived and using it I was able to measure boiler supply and returns of ~130 and ~82 respectively, for a delta of over 40 degrees. I'm not sure I'm even getting 1 GPM right now. I did turn off the thermostats for 6 of my 11 loops three days ago, so at most only 5 can be open which has seemed to improve the overshooting and undershooting for the remaining 5 loops.

    In any case, looking forward to having a pro out to take a look.
  • Gordy
    Gordy Member Posts: 9,546
    edited November 2013
    IR thermometer

    Make sure what ever you are shooting has black tape on it or you will get false readings. Especially shiny objects such as copper piping.

    Head loss is longest loop plus supply and return piping to the circ.

    The concern for the mix valve is to allow the boiler to run higher temps yet allow the floor to receive cooler water. Otherwise the boiler will live a short life. Ci boilers need min 130 return temps to burn off acidic combustion condensate or it will eat away the ci heat exchanger. Unless it's been cleaned you may notice flakes in the pan under the burners this is a sign of condensation.
  • knotgrumpy
    knotgrumpy Member Posts: 211
    Any update on this one?

    Just curious if the Tech has been to your house yet...

  • LMJ123
    LMJ123 Member Posts: 6
    Not yet

    I spoke to the contact SWEI provided last Wednesday, and was told that the person he wanted to come out was out of town through Thanksgiving, but would be back this week and I would hear back to set something up. If I don't hear back soon I'll give him a call again to check in.
  • tim smith
    tim smith Member Posts: 2,738
    edited December 2013
    Re: high useage and overshooting

    my best guess from the pics and the description is the boiler short cycles like mad due to no pri/sec piping and or buffer. Also probably raining condensate down at those water temps on to burner that will also cause short cycling. Temp gets too high in slab and overshoot.  Probably could really benefit from a buffer tank and maybe mixing also but could probably oversize buffer tank and use higher temp water from boiler above 135 or so to minimize condensation. Control system water temp from buffer tank  system side with reset control on that side of buffer. Just a semi educated guess from what I could see.
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