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Hydronic fin radiators don't seem to get hot enough

Good day all. 2 summers ago I replaced my cast iron oil fired boiler with a propane combi / mod; Dunkirk / ECR DCC205. I don't fully understand the BTU ratings but the input BTU is 164k, . The hydronic piping in the house is all unchanged, reused the same 2 circulators and Taco switching relay. I attached a picture of the set up and a drawn diagram / schematic of my near unit piping. Excuse the messy basement but the old oil fired boiler is still there and will keep it as a back up for domestic hot water for the time being in case I do additional work to the new combi set up. The new combi boiler and / or associated plumbing doesn't seem to heat the fin tube radiators anything like the old boiler did. I would come home from work, increase the Tstat from 65 to 68 and within 10 or 15 minutes the call for heat would end and could feel the warmth in the house. Now the new boiler just seems to keep running and takes hours for an increase in room temp for a similar situation / call for heat. The domestic hot water side works beautifully and never sets error codes and seems efficient. There are no gauges that display what the temps are in the hydronic lines so I can't see what the actual temps are of the circulating water other then the readout at the panel and the gauge that's located on the unit which displays normally 170 -180 when running. I don't know what the return water is.

A few questions- am I missing something here with my setup that you can quickly glean from my pictures? I also don't fully understand the operating concept with the supplied 1 1/4" pipe that circulating water can bypass right by the combi unit, dosen' really look like a closely spaced tee or hydraulic separation, again I assumer there is physics that I don't fully understand in the design. I did replicate and use components in the arrangement recommended by the manual.

I suspect that circulating water blows right by the combi unit without delivering energy to the fin tubes like the oil boiler did previously.

Thanks all in advance
Mario Labrecque, Rexford NY




Comments

  • GGross
    GGross Member Posts: 396
    I would suspect maybe you have some air in some of your baseboard. Sounds like the zone pumps are the same as before, and the boiler temp is similar, so what has changed? When changing the boiler it is possible that more air was introduced into the system than you may have realized, you have an air separator, but if you have a few pieces of baseboard that are airlocked, or half full of air that will greatly or entirely diminish the heat output

    The piping arrangement that you mention is fine. It is primary/secondary piping. Newer boilers use this piping method for a variety of reason, primarily to guarantee flow through the heat exchanger, and though it might not make sense it works. If it were in fact blowing past the unit, the boiler would eventually overtemp and shutdown, and likely leave you with an error code, likewise some of these units (not sure on this specific brand) would give you a delta T error, meaning the return water to the boiler and the supply temp, are either too close together or too far apart.
  • Ironman
    Ironman Member Posts: 7,076
    The tees are technically a little too far apart, but I don’t think that’s your issue.

    Is the outdoor sensor connected to the boiler and the ODR functional? If so, it’s gonna change the SWT as the outdoor temperature changes.

    A mod/con boiler modulates and attempts to supply water that’s just warm enough to heat the house. This provides the most comfort and economy. When you set the thermostat back and then up, you’re defeating the purpose. Set the thermostats at one constant temperature and leave them there.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    HomerJSmithbburd
  • marsfromrexford
    marsfromrexford Member Posts: 8
    oh wow thanks both of you for taking a look so quickly. Okay, some of the older fin tubes do have bleeders, I'll definitely check those and reflush / bleed. I do get error codes periodically; #E110 and 125 which in this case is related to lack of pump circulation. I had a tech come out and couldn't find a fault as it is a intermittent error setting. The tech told me that I should move the unit to an exterior wall and have shorter twin pipe run. I partially discounted that advise based on the fact that I'm pretty pleased the the performance of the DHW.

    I don't have the sensor, my local dealer says they never use them but I can definitely order one and install and set configure the settings as per the manual.

    Thanks!
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 13,127
    It's probably a control issue and you could be over pumping the system which makes no difference with the heat transfer but could throw the control system and boiler out of wack
  • HomerJSmith
    HomerJSmith Member Posts: 1,924
    You could have benefited from a hydronic separator. I like to see balancing valves on circulator zoning. You have one of three scenarios: insufficient flow, insufficient supply water temp from the boiler, or insufficient supply water temp because of return cold water mixing. I suspect it is return cold water mixing. Time to take some temp readings on the supply. As noted, your boiler closely spaced tees hardly qualify. Check boiler programing, also.
  • Ironman
    Ironman Member Posts: 7,076
    There should be a speed switch on the internal boiler pump. Try setting it to the highest speed.

    There should also be a manual bleed valve on top of the heat exchanger. See if you can get any air out from there.

    How long, and what size is the gas line? What other appliances are connected to it? Is this natural or LP gas?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • marsfromrexford
    marsfromrexford Member Posts: 8
    The internal pump (Grundfoss) does have what looks like an 'increase' slotted screw, yeah I'll mark it and increase it for sure.

    I'm pretty sure the system is free from air. I bleed the piping and always use the 10minute purge sequence if I open anything up. There is an internal bleed valve along with an automatic (air scoop) one just above the circulating pump

    I don't like the LNG valves at the tanks that the supplier set me up with. They gave a 2 stage valve outside at the tank which has 1/2 inch copper outside that runs under my porch about 10ft or so then directly connects to the 1 inch black iron stub that I installed. There's about 25ft if 1inch black that stops at my range than drops to 3/4 and runs another 10 ft to my combi boiler. I measured the water column at a tee near the furnace and got a static reading of 8.5 WC with a cheap amazon digital tester. the DHW works great. the furnace spec is 8-12 WC I believe. I don't trust the measurement I got and was thinking of having my gas supplier come and checking for me but they charge a fee for that.

    Thanks!!
  • Ironman
    Ironman Member Posts: 7,076
    Was the line under full load (boiler and stove firing at 100%) when you checked the pressure?

    If there’s any air trapped in the heat exchanger, purging the loops won’t remove it.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • marsfromrexford
    marsfromrexford Member Posts: 8
    Nope, everything was off. Is it valid to test at the drip tee near the furnace and not at the gas valve?

    Thanks Again
    Mario
  • Ironman
    Ironman Member Posts: 7,076
    It it should be.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • hot_rod
    hot_rod Member Posts: 18,209
    Does the copper tube at the baseboards get warm? If so you are circulating. What temperature does the boiler gauge read? Should be a readout in the control display and or a temperature gauge 

    A boiler supply sensor should be on the pipe to the left of where the expansion tank connects, just before the two circulator, if outdoor reset is used,
    Some boilers have a boost function to increase supply temperature if the heat call is too long

    Read through the control manual to see what functions are enabled
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • marsfromrexford
    marsfromrexford Member Posts: 8
    Having my questions discussed like this has been incredible for me thanks to all of of you.

    There is definitely circulation but I feel like they just are not getting as warm enough to keep up especially on extremely cold days .

    I used the drain outs and flushed the 3 hydronic circuits using a hose in a bucket with the concept being if there was air I would see bubbles and I did not. I recall that I would hear noise in the pipes if I had air in the past but the air separator that I have does a pretty good job. I do wish that the baseboards had bleeders like in the past but...

    I'm definitely not getting a good drop in return water. I measured in 2 ways; the panel displays boiler out temp but you can go into the display as mentioned and call up input temp and found that that temp is only 5 degrees cooler than the output. I also confirmed this using infrared / laser temp probe, although it's not as accurate I did notice that there is hardly any drop from end to end at each radiator in the house and only 5 degrees measured at the supply v. the return pipes. I wonder if I should add emitters?

    There isn't any sensors external of the boiler. I can't find the air temp sensor that the manufacturer recommends (Siemens QAC34) for sale locally and will have to supersede to something that is available but equivalent .

    Thanks!


  • HomerJSmith
    HomerJSmith Member Posts: 1,924
    If you are using a laser thermometer put a piece of black electrical tape on the pipe and shoot the temp on that. You will get better accuracy.
  • Ironman
    Ironman Member Posts: 7,076
    That sounds like you’re not getting good heat transfer at the BBs. Are they clean and the dampers open?

    You may also be over-pumping them. Can you slow the zone circulators down?

    Of course, this assumes that there’s proper output from the boiler.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • pedmec
    pedmec Member Posts: 713
    how much baseboard on each loop. how did you determine the size of the combi that you needed?
  • marsfromrexford
    marsfromrexford Member Posts: 8
    very naive about the whole combi purchase. the counterman sold it as 'well, your existing furnace is 117K and this one is 164K with 7x turn down and AI calibration so it should work' My upstairs has fin tube covering all exterior walls plus a kick space heater. The downstairs seems to be a bit sparse in fin tube coverage and thinking about adding 2 more 8 ft sections. Even with both upper and lower zones running I only get 5-10 drop in water temp measuring pre and post boiler. Past few days have been warm so haven't been really able to make any new observations about my system but the conversations I had have been tremendously helpful. I did order the book that was recommended and measure up all the radiators and get a better scheme put together.
  • hot_rod
    hot_rod Member Posts: 18,209
    Your old boiler was direct piped no doubt, no primary secondary. Correct. So if the boiler ran 180, that is what went to the beginning of the fin tubes

    When you pipe primary second the temperature blends in the closely spaced tees. How much it blends down depends on flow rate of the boiler pump compared to zone pumps.

    So even though the boiler temperature may be reading 180, you probably are not seeing that at the fin tube

    So with primary secondary, understanding the “blending temperature” they work best with the supply or boiler sensor strapped to the pipe a foot or so downstream of the closely spaced tees.

    This way the boiler is watching and adjusting the actual temperature to the fins

    The sensor can strap onto the pipe, insulate around it. Most boilers ship with that extra sensor in the parts bag. Check your manual for what was included with the boiler. Usually referred to as the system or CH sensor


    Don’t get hung up on delta T, it is an ever moving target in fixed speed pumping systems. It could be wide on start up and it will close up as the air temperature in the room, entering the fin tube warms.

    Also the faster, higher the flow rate in the fin, the more heat output. If those zone pumps are multi speed, try speeding up
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • marsfromrexford
    marsfromrexford Member Posts: 8
    My circulators are fixed, would it be worth trying a variable speed one? I understand you mentioned not to focus too much on delta T but I see thee are nifty circulators that have sensors for delta T measurements. After all this conversation I can't help but think that the radiators don't seem able to dissipate the heat entered by the boiler probably because of the lower circulating temps. I don't see any other sensor inputs, just the outdoor sensor. The manual is terrible, it's almost like it was written for cast iron boilers with no mention of primary / secondary piping and the fact that mod cons have different operating characteristics.


    Thanks Again,
    Mario
  • Ironman
    Ironman Member Posts: 7,076
    Does the system heat your house sufficiently?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Jamie Hall
    Jamie Hall Member Posts: 20,456
    Just remember this. The output of a baseboard is determined by the design of the baseboard, how well air is able to circulate over it, and the average temperature (end to end) of the water inside it. Nothing else. How fast the water is flowing is irrelevant, except that it affects the average temperature (for a given input temperature, faster flow will give a little more heat, as the greater amount of water doesn't cool as much going to the other end).
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 18,209
    I’d measure the temperature at the first fin tube on the loop, then the flow out of the last. Average those numbers. Say 160 supply, 150 return, so average is 155 average water temperature. Look at the output chart for that or similar fin tube to see the output per foot of fin

    Most fin tunBe spec sheets show the output a 1 gpm and 4 gpm. So the 4 gpm, higher flow will put out more heat.

    To increase heat output you need to either speed up the flow or increase the temperature to the fins.
    Getting more output is better done by increasing supply temperature. You can only do so much with flow increases. Sometimes you need to both increase flow and temperature to maximize output.

    Measure temperature at the baseboard to determine output, not the boiler.



    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    MikeAmann
  • marsfromrexford
    marsfromrexford Member Posts: 8
    Past couple nights were chilly enough observe the performance of the boiler. I guess my take away from all your guys input and rereading the manual is that condensing boilers are a bit of a different animal when making the comparison to regular cast iron boilers. It almost seems like less is more; I brought the circulator water way down to 150 and lowered the max BTU setting to 100K. Did the common sense things that was mentioned like double checking for trapped air, cleaning dog hair out of the fins and ordered the outdoor sensor that is back ordered of course. After making the adjustments and with lower water temp obviously I'm not getting the output at the fins as before with the old boiler but now the mod con seems to be working a lot smoother, nice and quiet, improved delta T with hardly any plume at the exhaust-big difference. I didn't even realize all the settings that are available and don't even think the parts counter or even the service techs in the area know about what was discussed here on this blog. The tech that was at my house last year couldn't explain the idea close tees and pri / secondary piping, wonder how many mod cons are out there not running as efficiently as possible. Now I'm obsessed with temping the circulating water but as far as now I think my situation is better thanks to you all.

    Again, big thanks to you all and found this to be an incredibly informative experience
    Mario
    IronmanMikeAmann