NRF22 versus NRF33 circulator

Toad

As our old Taco was nearing its end, it was suggested at each of the last two maintenance visits to consider replacing the pump. One shop recommended the NRF-33 and the other the NRF-22. Is there a material difference between these and would the system suffer much if it ended up with the “wrong” one? If so, what would the most likely symptoms or problems be? It is a 3-story home with boiler in the basement. This circulator would service all three floors but not the basement. Thanks.

EricPeterson

Short answer: As you may recall, I have a similar system (3 floors, converted gravity) with a combination of free-standing radiators and cast-iron baseboard. I use a NRF-22 and have no issues heating the house with that pump.
Long answer: Here are some references:
Pump Curves - from B&G
Article - from HeatingHelp archives
I calculated the EDR of my system as 908, then consulted the chart in the article which recommends a GPM of 20-25. At 3.5 ft of head (from the article), per the pump curves, it looks like a tossup: the NRF-22 is around 18 GPM, and the NRF-33 is around 28 GPM. I went with the NRF-22 because it seemed a slightly better match, and it costs less. From what I've read, I think the Taco 007 would be a suitable replacement.
Note: I think my calculated EDR is on the high side as some of the rooms have TRVs installed to avoid overheating.

Toad

Thanks Eric. This is very helpful and much appreciated. I assume I only calculate it for the radiators in that zone that are on that particular circulator, correct? Assuming I did it right, I came out just under 900. Does the fact that it needs to circulate it up three floors from the basement not play into the calc at all? If not, seems like the NRF-22 would be a fit.

Out of curiosity, do you know what you would see in terms of issues or symptoms if you did use the NRF- 22 where you should have used the NRF-33? (And vice versa.)

Thanks again.

EricPeterson

I would like to see the pros weigh in.
In fact both the NRF-22 and NRF-33 are circulators, not pumps, because they are moving water in a closed loop. Here is a quote from Contractor Magazine:
"Our industry friend Dan Holohan explains an operating circulator as being the functional equivalent of a ferris wheel ride. Once the ride is full, the weight of the people being raised to the top of the ride is countered by the weight of the people revolving to the bottom of the ride. The motor that actually performs the work isn’t really working all that hard, except when the ride is being loaded up. This is when the motor will struggle the most. Once the ride is loaded with people, the pump’s workload is significantly reduced."
As for the difference, perhaps the NRF-33 would be slightly noisier since the flow rate (GPM) is a bit higher.

hot_rod

If the former circulator was adequate, find a like sized model, regardless of the brand. Manufacturers all have cross over sheets.
There should be a circulator available to fit most any application. Many of the current circulators are multi or variable speed. So you could select a similar sized one one and dial it down to the lowest speed that will get the job done, assuring adequate heat delivery and flow thru the boiler.

ECM type circulators add the additional benefit of lower power consumption and some benefits like digital display.

EYoder

An NRF-25 might be a better option, it's a 3 speed. In between the 22 and the 33 but you can turn it down. And it's pretty cheap.