Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Increase maximum boiler temperature?

System details first, and additional background/questions/details are below:
  • 3750 sqft home, 3 floors, bulit in 1900, absolutely no insulation and all original windows, most without exterior storms
  • EVG-299 boiler, six zones all controlled by individual thermostats (photo below)
  • System supply temp is varried based on the ODT, max of 180F at 0F ODT, min of 120 at 70F ODT
  • Water pressure is approximately 20-25psi
  • 1.5 in L type copper boiler and circulation loop, Viega Barrier PEX5306 running from the circulation loop to the radiators in each zone
Below an exterior temp of 35F degrees or so, my system seems to be struggling to meet 68F degrees in the first floor rooms of my home (zones 1, 2, and 6). We've recently had a couple nights in the mid 20s (located in Pittsburgh, PA) and with the first floor thermostats set to hold 68F, the boiler ran constantly for 36 hours or so and the first floor maxed out at 66F.

I've done some digging on the maximum temperature for the boiler model, and the technical specifics for the copper pipe (400F) and PEX involved (200F at 80psi). Being mindful of maximum temps across the system I thought I'd try messing with the ODT curve to increase the supply temp to see if that helps warm things up, but wanted to check here first to see if folks more experienced than I had any concerns or other thoughts.

First, I'm planning to increase the maximum supply temp to 190F at 0F ODT. Since the boiler swings +/- 5F, I believe the boiler will then max out at 195F, but should still only target a max supply temp of 190F.

If this doesn't get the job done, then I figured I'd start raising the min supply temp from 120F in 5F increments until the first floor does maintain 68F. This is less ideal since in milder temperatures (50F or higher) the temp overshoots a bit.

The boiler also has a boost setting - not sure if I should turn that on? Or mess with the min/max ODT temperatures of the curve instead of the supply min/max temps?





Comments

  • unclejohn
    unclejohn Member Posts: 1,757
    Why does only one return have a air bleed. That valve thats 1/2 way open what are you tring do to with that?
  • Zman
    Zman Member Posts: 7,330
    In your previous post, it was determined that you need a bypass valve at the top of the system. Was that valve installed and is it closed? Why is the valve between the closely spaced tees partially closed (bottom middle)?
    I think it is far more likely that you have a flow issue or radiator sizing issue than a temperature issue. Do you have the ability to measure the supply and return temps at the individual zones?
    What speed are your circulators set to? Have you tried putting them all on speed 1?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • swedenumberone
    swedenumberone Member Posts: 12
    @unclejohn @Zman

    There are air bleeds at each radiator. I've bled each one and am confident there's no air in the system.

    The valve between the boiler loop Ts fully open - the picture is out of date.

    The bypass at the top of the circulation loop has been capped. I'm planning to put a valve in at some point, just haven't had time.

    All circulators are set to speed 1 (low)

    I have a "point and shoot" infrared thermometer I could use to measure the supply and return temps of each zone, not sure how accurate that would be though. I only have physical sensors on the common supply and return loop.

    With regard to radiator sizing - these are all original radiators. They are quite large, but I have no idea if that means they are ideal for heat transfer to the room nowadays.

    Radiator photos:





    Photos of current setup:



    Capped bypass:


  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,196
    Cat seems comfortable. Maybe the rest of the family just needs to sleep closer to the radiators!
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,196
    Seriously, The radiators were installed back in the day when they sized everything to keep the house, with no insulation, 85 F on the coldest day of the year with the windows open at night, .... ....with 20% more for the Husband (reference to a story by @DanHolohan "How did that heater get to be so big")
    You probably have plenty of radiator, as long as you have not removed any. Water temperature in the radiator needs to be just a few degrees warmer, adjusting the outdoor reset curve for precise indoor temperature control sounds good on paper, but in practice, you want to overshoot a little and let the thermostats do the work.

    With the house you described, a windy day (or night) will cause more infiltration than a calm day. so the right reset temperature on Tuesday might not be the right reset temperature on Thursday. It depends on the whether the weather is... well ... weathering... if you get my drift!
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
  • Zman
    Zman Member Posts: 7,330
    The IR thermometer will work well as long as the surface is not too shiny and you hold it pretty close. I would suggest putting electrical tape on the pipe and shooting it from a few inches away.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 11,997
    If the house is sluggish to heat then it's probably one of two problems.

    1. The house is under radiated or
    2. the water temperature is not high enough
    3. or the pumps are not moving enough water

    You need to study how the boiler is operating, this will tell the story. You say the boiler runs all the time. That is what a mod con is supposed to do. What percentage of firing rate does it run at? If the boiler is running at 100% and the house wont heat it's a flow or radiation problem.

    I think is is most likely a ODR curve issue
    EdTheHeaterManDZoroCanuckerHVACNUT
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,196
    @EBEBRATT-Ed
    I like the way you count!

    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
    ratioSTEVEusaPA
  • flat_twin
    flat_twin Member Posts: 318
    edited November 2019
    When you say it ran 36 hours continuously during the recent cold snap and barely maintainted 66 degrees, (I'm just west of you in OHio experiencing the same cold snap) could you distinguish between the circulators running or was the boiler actually firing 36 hours continuously?

    Did you live there with the previous boiler and piping system? If so how did it perform. Were you able to maintain set room temperatures?

  • DZoro
    DZoro Member Posts: 1,048
    Are your thermostats non-programable?
    I'd try increasing pump speeds to 3
    If that still doesn't work change 180*supply to 10* odt
    D
  • swedenumberone
    swedenumberone Member Posts: 12
    @flat_twin
    The both the circulators and boiler were running constantly, albeit the boiler was consistently running at 10-20% to maintain the target supply temp with two of the living area zones calling for heat. Remaining 4 zones were inactive - thermostats were set back from 68* to 60* as those zones were unoccupied. Unfortunately I don't know a thing about the previous system. New system was installed in March and I bought the house in July.

    @DZoro
    My thermostats are programmable (https://www.pro1iaq.com/t955wh).

    I've got the bedrooms and bathrooms set to 68* 5-8AM and 9PM-12AM, 60* all other times.

    I've got the kitchen/dining/living areas set to 68*4PM-12AM, and 60* all other times.

    It's going to be in the upper teens here tonight, will try progressively increasing pump speeds, and then adjust the ODT curve if the increased pump speed doesn't get the rooms to target temp.
  • Zman
    Zman Member Posts: 7,330
    An 8-degree daily setback and ODR are not compatible. The money you think you are saving with the setback will get eaten up by the boiler being forced into non-condensing mode.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • swedenumberone
    swedenumberone Member Posts: 12
    @Zman
    Is there a "generally accepted" maximum setback that optimizes the time the boiler spends in condensing mode? Or is it best to go with no setback at all to maximize energy efficiency?

    First home I've had with a hydronic heating system, so I'm still trying to figure out how to run this system in the most efficient manner. I'm accustomed to the 10* nightly temperature swings I had with forced air lol.
  • Zman
    Zman Member Posts: 7,330
    There is no magic number. It really depends on the system. You might play around with 3 or 4 degrees and see how hard your boiler has to work to bring it back up. Unless you like the cooler temps when you sleep, I would set it forget it with any high mass system.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • flat_twin
    flat_twin Member Posts: 318
    I don't do any kind of setback unless we're going to be gone for for three or more days. Even then it would only be a few degrees. I'm still puzzled about your supply water temperatures settings being rather high unless your house is really that drafty or under radiated. I'd be curious about the total EDR of your radiators. At any point did the heating contractor add up the radiator sections and calculate the output at a given supply water temperature?
  • swedenumberone
    swedenumberone Member Posts: 12
    @flat_twin
    I've not found the total EDR in any of the documentation the former homeowner left me. I'll take a crack and calculating it myself and get back to you.

    Side question for y'all now that I've done some research on condensation boilers and the fact that they only achieve their listed efficiencies with low return water temps (135F or less) - is that return water temp even possible with this system in an older house like this? I'm getting a delta T of 7-10 at most with all the zones running. With the default ODR curve its really not hard to push the return water temp above 135F.

    Maybe once I have new windows and the place fully insulated and can maintain 68F off of a lower supply temp, it's possible?
  • flat_twin
    flat_twin Member Posts: 318
    edited November 2019
    One other thing you mentioned was that your ODR was set for 180 degree SWT at zero degrees outside. I know you're in western PA and I'm not far away so I'll share this with you. I had my ODR set to max out at -5. Well guess what happened last winter when we had -18 and colder overnite for a period of a few days? I thought I'd try to ride it out but sure enough the house temperature sagged into the mid 60's. We keep the thermostat on 71 all the time. I was trying to walk a fine line to keep the boiler running non stop by running the lowest SWT possible. Cloudy windy days were a problem and the boiler couldn't keep up with those ODR settings. I bumped the SWT up just a bit overall and extended the low end down to -20. So now it cycles a little more on sunny calm days but keeps the mrs warm so all is good. We have old cast iron radiators and a mod con boiler.





  • flat_twin
    flat_twin Member Posts: 318
    edited November 2019
    Most old homes with big radiators are tighter than when the heating system was installed which allows them to run much lower supply water temps. In our case with improved windows, doors etc, the current heat loss is about 62k btu. The radiators are capable of 102k btu at 170 average boiler water temp. So this evening it's 9 degrees outside and the house is being heated with 122 degree boiler water. And it's condensing all the time.

    For now, do away with the night time setback altogether and see what happens.
  • DZoro
    DZoro Member Posts: 1,048
    That modulating boiler is your set back.
    You should see savings from that instead of large set backs.
    Understand bedrooms cooler, in our home we keep the master constantly cooler, just a thought. Master bath is constantly warmer ;)
    Just my .02 cents
    D
  • Jon_blaney
    Jon_blaney Member Posts: 273
    Set the desired temperature and forget it. The penalty may be in the cost of running the system but the reward is COMFORT.
  • hot_rod
    hot_rod Member Posts: 16,304
    Also keep in mind with un-insulated 2X4 walls between various rooms, you really cannot stop heat flow form hot to cold when trying to setback various rooms from one another. A guesstimate would be 5° or less between rooms?

    Remembering the higher the delta T between those rooms the greater the rate of heat transfer from hot to cold.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • swedenumberone
    swedenumberone Member Posts: 12
    Thanks everyone for all the help thus far.

    I upped all the pump speeds to high and adjusted the lower end of the ODR curve to 190F at 10F ODT (shown below). The 2nd and 3rd floor are hitting 68F just fine. The first floor is maintaining 68F during the day and 67F at night.

    @flat_twin You got me curious about total EDR. I started snooping around in the basement and in addition to noticing how drafty it was (probably another factor contributing the system struggling to heat the first floor) I found two empty holes in the floor in the corner of the kitchen that make me wonder if there was a fourth radiator on the first floor at some point that has since been removed. I found the "calculator" below, I'm getting a total EDR of 279 - does that seem appropriate for an 1,120 sq ft area with 10 ft ceilings?




  • flat_twin
    flat_twin Member Posts: 318
    edited November 2019
    This chart has average supply water temps at the bottom for hot water radiators. Am I seeing two column radiators in your pics? How tall and how many sections. https://www.expressradiant.ca/pdfs/product_classic_sizing_how_to.pdf

    279 EDR / 180 degree supply water is 47,430 btu.

    Compare that to the heat loss for the same area. Just curious, did you also find your total EDR for the whole system?