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Need Advice on the new boiler and what to do first with the current system

kuzyap
kuzyap Member Posts: 7
Hi,

I need advice on what to do with my 20 year old Laars mini therm propane boiler 160K BTU input. 131K out.

We moved into our house before last winter and the boiler couldn't keep up with the demand on the cold days during last winter.

The house was completely gutted and remodeled 20 years ago, it was an old barn. The house 6400 sq ft.

I have 10 total zones. 1 hot water, 1 driveway (we don't use it) and 8 heat zones. 2 out of the 8 heat zones a radiators with fins above ground. The other 6 are 2 are above slab, 4 are below wood.

There is a hot loop, medium loop and cold loop. Hot is for domestic water and wall radiators. Medium is for wood. Cold is for concrete.

On the cold days the boiler would run all day and if I had more than 3 zones calling for heat, the high temp loop would not reach 180 deg.

If I leave only one zone working and shut everything else off - the temperature would go up in that zone and
the high temp loop would reach 180 deg. There is Variable Speed Injection Mixing using a couple of Tekmar 356 controls.

I have an amtrol boilermate tank.

Heat Loss calculation was done. They guy who did spent two hours. He looked at the plans I gave him. Looked at the insulation and everything else. He said it was 160.

I am not sure if it is accurate.

I originally posted this on hvac talk and the people suggested to me to post it here.

Questions:
Every contractor is telling me to do different thing. One suggested a condensing boiler others suggest cast iron. One contractor told me to change all the pumps for more powerful pumps. One contractor told me to change pipe sizing.

Condensing 95% vs cast iron 85%? I would save about $400-500 a year with the 95%
but the contractor said the 95% is less reliable and doesn't last as long.

I have pictures of the current system and will post it later today.

Thanks,
Victor

Comments

  • kuzyap
    kuzyap Member Posts: 7
    https://photos.app.goo.gl/32qrRT5CQ8xyx6mN8

    First photo is boiler,
    Second is the hot loop -- 1 priority water, the other two are the radiators on the walls.
    4,5,6,7 is the medium loop - wood (2nd floor)
    11,9,2,3 is the cold loop - concrete (11 is off - driveway)
    B and C are mixing pumps. Each pump has a controller with outdoor sensor and a sensor on the pipe.
  • Jamie Hall
    Jamie Hall Member Posts: 18,940
    I'm not so sure your heat loss calculation which he gave you is too far off. That works out to about 25 BTUh per square foot, which for most northern climates is pretty good.

    So...

    A boiler which puts out 131K just isn't going to make it on a cold day (if your design outdoor temp is 10, and indoor 70 -- it will only hold 70 down to 20, for instance -- any colder outside and it will be colder inside, too).

    So... you're looking at a bigger boiler. Which one? Or even which kind (cast iron vs. mod/con)? They all have advantages. They all have disadvantages.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,689
    Responders can save a whole lot of typing and asking questions by reading the same post here:
    https://hvac-talk.com/vbb/showthread.php?2212743-Need-Advice-on-the-new-boiler
    steve
  • kuzyap
    kuzyap Member Posts: 7
    I had one suggestion to change the size of the pex for mixing from 3/4 to 1 inch and also change the 3/4 from boiler to water tank to 1 inch.

    I decided to put a new boiler in.
    I have a couple of quotes for viessmann boilers. One estimate is for vitodens 200 and the other one is for vitocrossal 300.

    Not sure what the difference is. One is freestanding the other one goes on the wall.
  • Zman
    Zman Member Posts: 7,330
    Ok,
    Here is what I think is going on. You have a boiler that is sized marginally to the heat loss.
    You have some very BTU hungry concrete slabs which are dragging down your system temps and causing the high and medium temp emitters to underperformed.
    The good news is that your tekmar 356 mixing controller is designed to prevent this if they are setup correctly. You need a sensor on the system return pipe at the boiler which the tekmar can read. You then need to set the boiler protection temp on the tekmar so it will slow the injection to the slabs when the boiler return temp drops. It will be trial and error to get the temp correct. My guess is that somewhere in the 140-160 range will work. While you are at it, check the outdoor reset numbers and report back. If you get confused, take the cover off the 356 and post a picture of the wiring.

    You could do the same for your medium temp zone but I don't think you will need to.

    https://s3.amazonaws.com/s3.supplyhouse.com/product_files/356-install.pdf
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    Ironman
  • Zman
    Zman Member Posts: 7,330
    It looks like the sensors are on the supply side to the left of the air scoop rather than the return side where they need to be.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • kuzyap
    kuzyap Member Posts: 7
    I will check the sensors today and report back
  • kuzyap
    kuzyap Member Posts: 7
    edited November 2019
    For the medium loop (Wood)

    It looks like everything is wired correctly:
    1) 8 and 9 are 24 V (R+ and C-)
    2) jumper between 7 and 9 (T and C-)
    3) nothing on the 5 and 6 (boiler)
    4) 1 and 4 are boiler supply sensor (Com and Boil)
    5) 1 and 2 are mixing sensor after the injection pump (Com and Sup)
    6) 1 and 3 are outdoor sensor (Com and Out)

    For the medium zone (wood)
    Settings:
    Room: 65
    Outdr DSGN: 0
    Terminal Unit: 2 (Low Mass Radiant)
    Mix Indr: 67
    Mix Dsgn: 140
    Mix Max: 160
    Boil: Supply
    Warm Weather Shut Down: 57
    Units of Measure: F

    The sensor is on the supply side.
  • Zman
    Zman Member Posts: 7,330
    edited November 2019
    Right, except to fix your issue the sensor needs to be on the return side and some settings need to be changed in the advanced menu. Someone needs to slide the dipswitch to advanced and change the settings noted in this markup.
    The cold loop is the one causing your issue.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    HVACNUT
  • kuzyap
    kuzyap Member Posts: 7
    I can access the advanced menu. It would be easy to change the sensor and put it on the return side. Should I put it next to the boiler on the return side. I will switch the boil: Return. What other settings should I change? I thought concrete should not be set > 140.

    There is also and issue in the wood loop (medium)
    Today I had the wood zones working and the thermostat was set to 65 but the temperature in the bedroom was 62. The heat call was on all night. I raised Mix Dsgn temp to 150 to see if it helps.
    I don't think the zone is hot enough.

    For the low zone (concrete)
    Settings:
    Room: 65
    Outdr DSGN: 0
    Terminal Unit: 1
    Mix Indr: 67
    Mix Dsgn: 120
    Mix Max: 140
    Boil: Supply
    Warm Weather Shut Down: 57
    Units of Measure: F

    Thanks!!


  • Zman
    Zman Member Posts: 7,330
    Yes, put it on the boiler return pipe a foot or so away from the boiler inlet. And yes change the the controller setting to sensor on return and the boiler min to 160 for the slab loop and 155 for the wood floor loop for now.
    The default settings for term unit 1 for the slabs and term unit 2 for the wood is a good place to start.
    The idea of all of this is to keep the boiler in non condensing mode and keep the temps high enough so that your high temp zones will be satisfied. I believe the issues your are having with the warm and hot zones will go away once you set it up correctly.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • kuzyap
    kuzyap Member Posts: 7
    Can the cast iron boiler go into condensing mode?
  • Zman
    Zman Member Posts: 7,330
    A handful of cast iron boilers are OK condensing only if they are specifically designed for it.
    Your boiler is a low mass copper fin. It does not do well with condensing or low flow conditions
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein