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# How do I know the system circulator is the right fit

Member Posts: 197
I have roughly 75 feet of baseboard over three separate zone valves. How do I select the best circulator?

Zone 1 26 feet
Zone 2 18 feet
Zone 3 30 feet

• Member Posts: 6,527
I has more to do with the pipe size and length.
"If you can't explain it simply, you don't understand it well enough"
Albert Einstein
• Member Posts: 1,275
btu's of the zone divided by 500 x delta tee ( that gives your g.p.m. )
then to get your head pressure you take the total length of pipe (longest zone) then you multiply by 1.5 elbows and other fitting) divided by .o4 that will give your feet of head.
then use the charts of the pump manufacture to give your pump size .
file:///C:/Users/u192772/AppData/Local/Temp/SelectingCirculators-1.pdf
• Member Posts: 197
Thank you @Snowmelt @Zman the size of baseboard itself is 3/4 copper pipe but the piping in the system to the baseboards are 1/2 inch
• Member Posts: 1,633
That's really odd. How is this piped? Is it a monoflo system? Maybe all of the baseboards are run in a home run to a manifold at the boiler?
• Member Posts: 197
@SuperTech 3 separate zones - each with a supply and return. The piping in the walls are 1/2 inch.
• Member Posts: 1,633
I just can't see that functioning correctly. Are you zoning with circulators or zone valves. Can you please post pictures of the boiler and piping?
• Member Posts: 14,738
If the baseboard is sized correctly, your 30' zone may require 15,000 BTU/hr. (500 btu/ft)
That is possible with 1/2" copper. The length of the piping, number of fittings should be in the head calculation to size the circulator.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 197
@SuperTech - a Grudfoss UPS1558FRC circulator as the system pump feeding three Honeywell Zone Valves. I'm not at the property today but will post pictures when i get back there on the weekend.
• Member Posts: 197
@hot_rod how do I calculate the length of piping, number of fittings that are in the walls?
• Member Posts: 14,738
Le John said:

@hot_rod how do I calculate the length of piping, number of fittings that are in the walls?

Probably estimate the distance but guesstimate the fittings. I think Taco suggests a multiplier piping length X 1.5 to get a ballpark #

The majority of the time a small multi speed 15-58, or other brand equivalent, covers a wide range of residential applications.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 1,958
Why 1/2" Supply and return lines?
• Member Posts: 197
@pecmsg The supply and return manifolds are 1 inch but gets reduced to 1/2 inch after the zone valve. The heating loops in the entire house was done in 1/2 inch copper. I don't know why.
• Member Posts: 2,256
There is nothing wrong with using 1/2 pipe to smaller zones. We do it all the time with panel radiators. As long as you have adaquite flow per the zone size (30' fin tube in your case). The smaller piping does create extra head, but most residential size systems are short enough that most reasonable sized circulators have no problem supplying the required flow.

No reason to always use 3/4 pipe, it is just most commonly used.
Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
• Member Posts: 197
Thanks @Solid_Fuel_Man so is the Grundfoss UPS 15-58FRC a good pump for the application? I thought based on the formula above I needed something like an Alpha 2 1558 or a Taco VT2218?
• Member Posts: 1,633
Both pumps are you mentioned are great and can cover a wide range of flow requirements. I'm a fan of both pumps but I have found that the Alpha is great for zone valve applications.I suppose that just because the 1/2" pipe is unusual doesn't make it completely wrong.
• Member Posts: 6,527
There is nothing wrong with 1/2" supply and returns, especially since your largest zone is only ~15k/btu.

If your 15-58 is working well, I don't know that I would bother changing it. You can set it on the lowest speed that will give you satisfactory heating. A 20 degree supply/return delta t would be a good indication.

The other circs you mentioned would be a nice upgrade and would save a few bucks in electricity.
"If you can't explain it simply, you don't understand it well enough"
Albert Einstein
• Member Posts: 2,256
I bet even on the lowest setting, there the delta T will be less than 10 degrees.
Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
• Member Posts: 197
with about 70 feet of baseboard with a 15-58 on speed 1 - getting between 7 and 8 as a delta T when all three zones call for heat. I'm wondering if switching to a lesser pump like a TACO 003 or 006 would increase the delta T? The Lochinvar Noble needs 5GPM minimum flow (I think).

System heats just fine just trying to get a higher delta T.
• Member Posts: 678
That 20 degree delta is based on your design day conditions. Were you at or near those conditions when you took the measurements? On any warmer day your delta will be smaller
You can have it good, fast or cheap. Pick two
• Member Posts: 8,796
@Le John

Just check the temperature in and out of the baseboard on each loop.
If your TD is less than 20 and it is heating the house as you have indicated then your fine. Check this with all zones calling.

If you can balance the flow between the zones (based on inlet and outlet temperature) I would do that but I would not choke the flow to get to 20 deg TD. Boilers last longer with enough flow

I wouldn't go looking for trouble
• Member Posts: 14,738
Is the system heating OK? Keeping up on design days? Do you have boiler short cycling issues? Turn all the stats down, let the ambient drop to 68 or lower, fire up and measure delta. 20 or higher?

Observe for 30 minutes, I suspect it will continue to drop unless you are at design temperatures outside.

Don't get too hung up on delta T across the system, it can and will move around. If the system is near shutting down, satisifing the load, expect that delta to close up

It will go to 0 when then load is satisfied

If it is direct piped you will only be able to run the gpm down to the point that Lochinvar allows, more you may end up going to high limit on the boiler. Really no reason to operate the boiler by bouncing off high limit.

Here is a good read explaining how heat transfer works and the truth about delta T.

https://www.caleffi.com/sites/default/files/file/idronics_23_na.pdf
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream