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Is my circulator undersized?

On Christmas day my boiler pump started making a terrible racket.

Turned out it was a failed coupler on my B&G Series 100 NFI.

I had a spare pump, a B&G NRF-22 that came with the new boiler I installed in 2010, and that I had set aside for just this situation.

This new NRF-22 pump seems to be doing fine, but is it a good fit for my needs?

On paper this pump might be undersized for my converted gravity system.

My system has three zones (one pump, three zone valves):

Zone1 - EDR=112.2 GPM=2.7 (first floor FR and kitchen)

Zone2 - EDR=299.6 GPM=7.5 (first floor LR, DR, Foyer, finished basement)

Zone3 - EDR=496.2 GPM=11.6 (second and third floor, 8 rooms)

Total - EDR=908.2 GPM=21.3

EDR was calculated by adding the values for all the radiators in my system.

The GPM values are extrapolated from a table posted in a previous Wall post:

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According to this post, the NRF-22 has these maximum values:

NRF-22: GPM=17 EDR=725

Thing is, the system load depends on which zones are calling for heat.

Should I move up to a higher capacity pump like the B&G NRF-33?

Or are there better choices out there?

The NRF-22 does sound like a cheap timer.

Your thoughts?


Eric Peterson


  • Paul48Paul48 Posts: 4,492Member
    edited January 2014

  • IronmanIronman Posts: 5,091Member
    edited January 2014
    Feet of Head?

    You missing a major component in calculating the size of circ required: feet of head, aka resistance to flow. Don't mistake this for elevation which produces static head: that is not a factor in a closed loop.

    From the EDR total that you listed, you would have a btu output of 136,200 at the standard operating temp of 170* average. Calculating with standard 20* delta T, you would need 13.6 gpm, not 21.3. Can the NRF-22 produce 13.6 gpm with the resistance in your piping? Probably not. But we don't know what that resistance is until it's calculated.

    It appears that you have large pipes and the system was once gravity flow. That's a good thing because that means it will have a low resistance to flow. I'm gonna GUESS and say it's probably not more than 4 ft. of head. The zone valve may add another 4 ft. of head for a total off 8 ft.

    I don't have the pump curve for the NRF-22, but that's what you'll need to check to see if it could delivered 13.6 gpm @ 8 ft. of head. It probably can't.

    The Taco 007 is their equivalent of the NRF-22 and I've attached the curve for it. Line 5 is the 007's curve. You'll notice that at 8 ft. of head, it will deliver 8 gpm. The NRF-22 would be close to that.

    Again, I'm guessing at your systems head. It could be higher or lower.

    Your system may also function satisfactory with a higher delta T which is what you'll have if the gpm is less than 13.6 gpm.

    Here's what I'd recommend: turn all your thermostats up and let the entire system reach it's operating temp (hot). Using an accurate strap on or infrared thermometer, measure the supply and return temps a the boiler. Then measure them from each set of run outs going to the rads. If they're all reasonably close and your not exceeding a 25* difference (delta T) at the boiler, you may be OK with the NRF-22.

    The simple question is: does each room feel comfortable? If so, then the circ is sufficient. The only caveat being that you don't want to get much more than a 25* delta T at the boiler (if it's cast iron) to prevent flue gas condensation.

    If you want to upgrade the circ, then I'd look at a variable speed delta T circ of sufficient size.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • M LaneM Lane Posts: 123Member
    B&G couplings

    just fail at times. The springs eventually get enough back and forth flex that they snap. Its been my experience that the pumps that run 24/7 have this happen a lot less than the ones that start/stop with TT or setpoint demands.

    I suggest replacing the motor mounts as well, a shifting motor will cause the coupling to break too.

    And put in B&G oil. DO NOT pt in Zoom Spout oil; it has detergent which B&G says is a no-no. When I buy a Zoom Spout, I dump the oil and replace it w/ non-detergent oil. Of course, we here in Denver don't tell this to the apartment maintenance guys (job security)
  • jumperjumper Posts: 1,339Member
    ditto to Onsightmechanic

    Continuous is easier on pump & motor as well as coupling. I don't know if there is such a thing as an undersized circulator for a home heating system. Unless it's for one of those copper boiler that requires velocity. I've seen teeney circulators do well on multi-unit buildings. On cold days the limits are reset.
  • SteamheadSteamhead Posts: 13,051Member
    edited January 2014
    What is your ΔT

    across supply and return, measured with all zones on, and also with only the smallest one on?
    All Steamed Up, Inc.
    "Reducing our country's energy consumption, one system at a time"
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Baltimore, MD (USA) and consulting anywhere.
  • SWEISWEI Posts: 7,356Member

    Series 100 is very close to a 0010 curve on the chart above.  The NRF will consume a bit less power but it will not last for generations like a Series 100 will -- especially in a high temperature system.

    Ditto on the oil - you want ISO 68 turbine oil or similar.
  • EricPetersonEricPeterson Posts: 48Member
    edited January 2014
    Feet of Head?

    Yes I am missing the head component - I can work on calculating the head from what I know of the piping in the house.

    Yes I have large pipes and the house was originally a gravity system. The near-boiler piping is all 1-1/4", from there it starts out as 3" pipes for Zone 2 and Zone 3, which get reduced. The zone valves are all 1-1/4" WR.

    Yes each room feels comfortable. I have an IR thermometer on order, will report back with the deltas Ts.

    Yes I have a cast iron boiler - Burnham ES27NI-G NET I=B=R Rating 155 MBH.

    The house was built with no insulation, thus the original radiators are now oversized as the house has had insulation added.
  • EricPetersonEricPeterson Posts: 48Member
    What is your ΔT

    I have gauges on the supply and return. Based on these gauges, the delta T is about 25F, both with all three zones open and also with only the smallest zone open.

    My system does have a system bypass, regulated by a valve. The valve position seems to be working OK as I have left it alone since the install. My thought was to replace this valve someday with a 3-way thermic valve.

    It is -15F here today, and the system seems to be holding up fine.
  • Mark EathertonMark Eatherton Posts: 5,843Member
    I think you are fine..

    Just make certain that the return water temperatures are above 140 degrees F for a non condensing appliance, and the best way to guarantee that (as you already know) is with a 3 way thermostatic non condensing valve on the return.

    You are giving it an acid test right now, and it looks like its getting a good passing grade to me based on what you've posted.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • EricPetersonEricPeterson Posts: 48Member
    I think you are fine..

    Well now that is an interesting point concerning the return temperature, and something I researched prior to choosing the ES2.

    Burnham states that the minimum return water temperature for this boiler is 110 (°F) - which is one of the reasons I chose the ES2. They also recommend a bypass or PS to avoid thermal shock, which is why I put in a system bypass.

    Typically I see a return temperature of 125 to 130 (°F) going into the boiler which is well above the Burnham requirement, but I also realize well below the generally accepted minimum of 140 (°F).
  • Mark EathertonMark Eatherton Posts: 5,843Member
    My bad...

    This is not my grandfathers cast iron. It's like the Germanic design with Silicon, which is more resistant to the corrosive tendencies of condensate. Hence why they allow a lower return. It doesn't mean that you won't get any byproducts of combustion in the lower sections of the heat exchanger, only that it will not degrade like regular cast iron will.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • EricPetersonEricPeterson Posts: 48Member
    Would still like a higher return temp

    But have not figured out the best way to achieve that, keeping in mind the original topic of this post which was the pump size.

    By "best" I mean the simplest configuration that achieves all the design goals: avoid thermal shock, provide adequate GPM to system, and (optionally) increased return temperature.

    "Simplest" means fewest components, and minimal technology.
  • EricPetersonEricPeterson Posts: 48Member
    Feet of Head?

    Closing out this thread.

    Answer to "The simple question is: does each room feel comfortable?" - YES. I am in northern IL and we have seen temps down to -20F this winter. I did have to raise the high limit to 170F on the coldest morning.

    A simple head calculation (multiply longest pipe run by 0.06) leads me to believe the head is somewhere between 6 and 8. The pump curve for the NRF-22 indicates a GPM of 12 to 14, so I am pretty close to that 13.6 GPM:

    Other B&G options would be the NRF-33, or the 3-speed NRF-25.

    Or I could simply repair the coupling on my Series 100 pump - but I like the NRF-22, it is much quieter.

    Installing a thermic bypass valve will help with any delta-T issues, though as I have pointed out it does not seem to be much of an issue from my observations.

    Thanks everyone for your comments.

  • EricPetersonEricPeterson Posts: 48Member
    Will Series-100 push water farther than NRF-22?

    I recently noticed that the baseboard radiator on the 3rd floor of my house is stone cold.

    We have not used this room since before Christmas, when it was working fine.

    On Christmas Day, I swapped out my Series-100 with an NRF-22 which was the start of this whole thread. That is the only change I have made to the system.

    So does the NRF-22 not have enough head to push water to this radiator?

    It is the furthest one from the boiler (located in the basement).

    The other radiator on the third floor is a large free-standing one and it heats up fine.

    All the third floor radiators are on the same zone as the second floor radiators, but there are two sets of pipes.

    The warm 3rd floor radiator is served by pipes that branches to two other radiators on the second floor (both have TRVs turned all the way down).

    The cold 3rd floor radiator is served by different pipes that branch to three other radiators on the second floor (two on full blast, one limited by a TRV).

    I have ordered a replacement coupler for my Series-100 and will swap it back in to see if that solves this problem.
  • Mark EathertonMark Eatherton Posts: 5,843Member
    ESBE Thermic valve

    Doesn't get any simpler...

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • EricPetersonEricPeterson Posts: 48Member
    ESBE Thermic Valve - Piping Question

    Since I have your attention....Thanks for your help in the past - here I am, back with another question.

    I have a converted gravity system with an atmospheric boiler, am looking for boiler protection, so have been looking at the Danfoss Thermic valve installed on the return. But I have a question concerning their attached piping diagram ("Gravity/Large Volume Hot Water Systems:").

    Danfoss says: "The recommended piping allows the heat source to handle the returning water while providing heat to the system."

    When the valve is closed, the left pump is cycling water through the boiler, and the right pump is separately cycling water through the system. No heat is being provided to the system. Once the valve opens, the left pump would be able to push water through the boiler and the system.

    My question: what it the purpose of having the two pumps? One pump seems to me like it would be sufficient.

    The only reason I can come up with is that due to the system head, the water would tend to flow primarily back to the boiler rather than to the system. But it seems like that could be adjusted using the flow control valve. I am just trying to keep things as simple as possible here.


    Eric Peterson
  • ToadToad Posts: 4Member
    Eric - did you ever try the Series 100 again? Were you able to resolve the issue of the cold 3rd floor radiator? I am having the same issue with one of my three 3rd floor radiators (baseboard one cold, two traditional ones hot) and have just had the old Taco 110-144 circulator replaced with the NRF-22. Wasn’t sure if air was still trapped somewhere (but have successfully bled all radiators) or if it could be issue around the circulator, or something else. Any learnings from your 2014 experience would be greatly appreciated.
  • IronmanIronman Posts: 5,091Member
    edited February 11
    What's the pressure on the boiler gauge when it's cold? Is your pump on the return side of the boiler?

    Starting a new thread with some pics of the boiler and its near piping will get you better responses than tagging on to the end of a five year old post.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • ToadToad Posts: 4Member
    Thanks @Ironman. I will try to do that. I had added to end of the @EricPeterson old message only because it was the identical issue and I figured after 5 years he had hopefully resolved it and could offer his insights. I’m brand new to this site, so apologies if I have not followed proper protocol.
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